Kirtland’s Warbler (Setophaga kirtlandii): COSEWIC assessment and status report 2024

Official title:  COSEWIC assessment and status report on the Kirtland’s Warbler (Setophaga kirtlandii) in Canada

Endangered 2024

COSEWIC assessment summary

Assessment summary - May 2024

Common name: Kirtland’s Warbler

Scientific name: Setophaga kirtlandii

Status: Endangered

Reason for designation: The global breeding range of this colourful wood-warbler is restricted to large regenerating stands of even-aged Jack Pine and Red Pine in Michigan, and adjacent states and provinces. In Canada, it nests only in Simcoe and Renfrew Counties, Ontario, with additional breeding season observations in southwestern Ontario and Quebec’s Pontiac region. It primarily overwinters in the Bahamas. The global population is estimated at fewer than 5,000 birds, with only about 40-50 mature individuals currently occurring in Canada. Birds are limited by the availability of suitable nesting habitat, and threats include wildfire suppression resulting in loss of early-successional habitats; conversion of nesting and wintering habitat for agriculture, forestry, and human development; and impacts of climate change and increasingly severe weather throughout the annual cycle. In the absence of management initiatives forest succession may lead to loss of suitable breeding habitat in Canada, as is the case in the United States.

Occurrence: Ontario, Quebec

Status history: Designated Endangered in April 1979. Status re-examined and confirmed in April 1999, May 2000, April 2008, and May 2024.

COSEWIC executive summary

Kirtland’s Warbler

Setophaga kirtlandii

Wildlife species description and significance

Kirtland’s Warbler (Setophaga kirtlandii) is a small songbird of the family Parulidae (North American wood-warblers). Adult males in breeding plumage have bluish-grey upperparts, a lemon-yellow throat and belly, and black streaks on the flanks and sides. Females are similar to males, but their plumage is duller, with grey or brown upperparts, a pale yellow belly and less distinct breast streaks.

Kirtland’s Warbler has special significance because it has a very restricted global distribution: it is the only bird species in North America to breed exclusively in 5 to 20-year-old Jack Pine and Red Pine forests. It is therefore an emblematic species of the pine barren ecosystem.

Aboriginal (Indigenous) knowledge

All species are significant and are interconnected and interrelated. There is no species-specific Indigenous knowledge in this report.

Distribution

Over 95% of the global Kirtland’s Warbler population breeds in Michigan, in the U.S., with the majority of individuals (> 98%) found in the northern portion of Michigan’s Lower Peninsula and smaller numbers found in the state’s Upper Peninsula and in Wisconsin. In Canada, the species is currently known to breed in Simcoe County and Renfrew County, Ontario. Additional breeding season observations have been reported from near Kenora, Ontario, in the west, to the Pontiac region of Quebec, in the east. Small numbers of individuals are recorded every year in southwestern Ontario during spring migration (max. 5 to 10 individuals per year). Kirtland’s Warbler overwinters primarily in The Bahamas, with additional records from the Turks and Caicos and at least one record from Cuba.

Habitat

During the breeding season, Kirtland’s Warbler is restricted to extensive young, dense, even-aged stands of Jack Pine or Red Pine containing small openings. The species is area-sensitive, generally occurring in habitat patches of less than 32 ha. In Canada, Kirtland’s Warbler breeds in Jack Pine stands, as well as in mixed Jack Pine–Red Pine and Red Pine-dominated stands. In Michigan’s Lower Peninsula, where the majority of the global population occurs, most birds breed in Jack Pine stands actively managed for the species. In winter, Kirtland’s Warbler mainly occupies broadleaf scrub habitat with well-drained soils and a dense undergrowth of native fruiting species.

Biology

Kirtland’s Warbler is generally monogamous. First breeding occurs at one year, and generation time is estimated at 2.2 years. The clutch contains 3 to 6 eggs, and most pairs raise only one brood per season. Brood parasitism and egg and nestling predation by the Brown-headed Cowbird can limit reproductive success. Kirtland’s Warbler feeds on both insects and fruit year-round.

Population sizes and trends

The current Kirtland’s Warbler population in Canada consists of roughly 40 to 50 mature individuals (based on counts at sites with confirmed observations), although numbers are approximate as survey and monitoring protocols vary by site. At Garrison Petawawa in Renfrew County, 1 to 5 singing males and 0 to 2 nests were found annually from 2006 to 2022. At one site in Simcoe County, the species has been documented annually since 2013, including confirmed nesting in 2013 to 2014. Since 2012, up to four individuals have been observed annually in suitable breeding habitat at other Ontario sites—albeit not at the same site each year—notably in Simcoe County and the Georgian Bay area. In western Quebec, at least four individuals of the species—three males and a female—have been detected since 2016 in suitable breeding habitat.

Overall, the core population on Michigan’s Lower Peninsula has increased since the 1990s, according to the census of singing males conducted regularly in the region since 1951. Over 2,000 singing males have been counted annually since 2011, including 2,245 males on the most recent census in 2021. However, declines have occurred since 2021 due to decreased habitat availability, which is predicted to result in population declines of 20 to 50% within the next decade. The Wisconsin population is small, but has persisted since 2008. Although immigration into Canada occurs, the supply of suitable nesting habitat in Ontario and Quebec is very limited, such that rescue is unlikely to change the species’ status.

Threats

Major threats to Kirtland’s Warbler include the reduced quality of breeding habitat owing to fire suppression and the maturation of current pine plantation habitat; the loss and fragmentation of breeding, migration and wintering habitat; and potential brood parasitism by the Brown-headed Cowbird. Additional threats include direct mortality and reduced habitat availability and quality due to climate change-related effects; the spread of invasive plants on the breeding and wintering grounds; and human disturbance from military base activities. In addition, Kirtland’s Warbler is typically single-brooded, further limiting its population growth.

Protection, status, and recovery activities

In Canada, Kirtland’s Warbler is listed as Endangered under the Species at Risk Act. It is also protected by the Migratory Birds Convention Act, 1994. In Ontario, it is listed as Endangered under the province’s Endangered Species Act. In Quebec, it is partially protected under the Loi sur la conservation et la mise en valeur de la faune [Act Respecting the Conservation and Development of Wildlife]. In the U.S., Kirtland’s Warbler was listed as Endangered from 1973 to 2019, but was subsequently de-listed because the recovery plan objectives were met. In The Bahamas and Turks and Caicos, Kirtland’s Warbler habitat in national parks has legal protection, although this represents a minority of the total suitable wintering habitat. Its NatureServe rank is G3 (Vulnerable) globally; S1B (Critically Imperilled) in Ontario; SNA (Not Applicable) in Quebec; S3 (Vulnerable) in Michigan; and S1B (Critically Imperilled) in Wisconsin. In 2017, based on the federal action plan for the species, restoration of Red Pine–Oak habitat began on two parcels of land in Simcoe County, Ontario, with singing male Kirtland’s Warblers detected there for the first time in 2022.

Technical summary

Setophaga kirtlandii

Kirtland’s Warbler

Paruline de Kirtland

Range of occurrence in Canada: Ontario, Quebec

Demographic information

Generation time (usually average age of parents in the population)

Estimated at 2.2 years.

Based on Bird et al. 2020

Is there an [observed, estimated, inferred, or projected] continuing decline in number of mature individuals?

No.

Inferred to be relatively stable over the last 10 years based on surveys in known breeding locations in Canada.

[Observed, estimated, or projected] percent of continuing decline in total number of mature individuals within 3 years.

Not applicable.

No evidence of continuing decline.

[Observed, estimated, or projected] percent of continuing decline in total number of mature individuals within 5 years.

Not applicable.

No evidence of continuing decline.

[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over the last 10 years.

Unknown; the small population appears stable over this time frame.

Based on surveys in known breeding locations.

[Projected, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over the next 10 years.

Unknown.

Based on surveys in known breeding locations, population appears small but stable. Declines possible over next 10 years due to habitat succession.

[Observed, estimated, inferred, projected, or suspected] percent [reduction or increase] in total number of mature individuals over any period of 10 years, including both the past and future (up to a maximum of 100 years in future).

Unknown.

Are the causes of the decline clearly reversible?

N/A, although the causes of historical decline in the U.S. are partially reversible.

Habitat creation and cowbird management policies have helped to reverse the past decline in the U.S., where most of the global population resides.

Are the causes of the decline clearly understood?

Not applicable, although the causes of historical decline in the U.S. are understood.

Historically, habitat loss and fragmentation; fire suppression; brood parasitism by Brown-headed Cowbird.

Are the causes of the decline clearly ceased?

Not applicable.

No recent decline in Canada, although habitat succession on managed lands in Ontario has potential to cause future decline and, in Michigan, is projected to cause declines over next 10 years.

Are there extreme fluctuations in number of mature individuals?

No.

Extent and occupancy information

Estimated extent of occurrence (EOO)

83,620 km²

Calculated based on minimum convex polygon around confirmed breeding season occurrences in suitable habitat. Includes all sites occupied during the 20-year period of 2004‒2023, plus three historical sites where habitat continues to be suitable (see Extent of occurrence and area of occupancy).

Index of area of occupancy (IAO), reported as 2x2 km grid value

Maximum of 56 km²

Estimated using 4 km² grids superimposed over each site used to calculate EOO. Estimated value for each site is based on known area of suitable habitat at two sites with multiple Kirtland’s Warbler territories (Petawawa and the primary Simcoe County site).

Is the population “severely fragmented”, that is, is >50% of individuals or >50% of the total area “occupied” (as a proxy for number of individuals) in habitat patches that are both (a) smaller than required to support a viable subpopulation, and (b) separated from other habitat patches by a distance larger than the species can be expected to disperse?

1. Yes, although suitable breeding habitat for the species is present in Canada, habitat patches are small and isolated
2. No, species is capable of dispersing back and forth between Canadian habitat patches and U.S. source population

Number of “locations”.

3 in Canada.

Locations are geographically distinct and therefore subject separately to threats such as wildfires and extreme weather events.

Is there an inferred continuing decline in extent of occurrence?

No.

Not estimated in previous status reports. Persistence of breeding birds at Petawawa and Simcoe County and increased breeding season sightings in Ontario and Quebec over the past 10 years suggest that the EOO has not declined over the past 10 to 15 years.

Is there an inferred continuing decline in area of occupancy?

No.

Not estimated in previous status reports. No inferred continuing decline in IAO over past 10 to 15 years.

Is there an inferred continuing decline in number of subpopulations?

Not applicable.

Only one subpopulation.

Is there an inferred continuing decline in number of “locations”?

No.

Two locations have been occupied annually for > 10 years. The third location (Henvey Inlet) was not occupied between 2020 and 2022 following a large wildfire, but 4 males were found in nearby regrowth in 2023 (though breeding was not confirmed there).

Is there an inferred continuing decline in [area, extent and/or quality] of habitat?

Possibly.

Early-successional habitat species. Often shifts geographic range as new habitat is created through wildfires and replanting. Succession in the primary occupied habitat at Simcoe County is a potential concern in the next 10 years, though ongoing habitat creation elsewhere in the same area may offset this loss.

Are there extreme fluctuations in number of subpopulations?

Not applicable.

Are there extreme fluctuations in number of “locations”?

No.

Are there extreme fluctuations in extent of occurrence?

No.

Are there extreme fluctuations in index of area of occupancy?

No.

Number of mature individuals (by subpopulation)

Total: Approximately 40 to 50 mature individuals.

Based on surveys in known breeding locations (see Table 1). All Canadian individuals are part of the same subpopulation. See Abundance.

Quantitative analysis

Is the probability of extinction in the wild at least 20% within 20 years, or 10% within 100 years?

Unknown.

Analysis not conducted.

Threats

Was a threats calculator completed for this species?

Yes, on 3 August 2023 (see Appendix 1)

Overall threat impact: High - Medium.

Key threats were identified as:

1. Agriculture and Aquaculture (IUCN 2) – Medium - Low impact: conversion of breeding and wintering habitat to crop agriculture and non-native pine plantations; habitat loss at the primary Canadian breeding site, a pine plantation, due to ageing trees and lack of a management plan
2. Natural System Modifications (IUCN 7) – Medium - Low impact: wildfire suppression resulting in loss of early-successional habitats; wildfires in breeding habitat; dominance of non-native plant species, reducing availability of native forage species in breeding and wintering habitat
3. Human Intrusions and Disturbance (IUCN 6) – Low impact: military base training activities
4. Invasive and Other Problematic Species, Genes and Diseases (IUCN 8) – Low impact: predation by feral and domestic cats; nest parasitism by Brown-headed Cowbird
5. Climate Change and Severe Weather (IUCN 11) – Low impact: loss of Jack Pine habitat in breeding range due to warming climate; rising sea levels and severe droughts on wintering grounds; extreme weather events (for example, hurricanes) throughout annual cycle

What limiting factors are relevant?

• Early-successional habitat specialist that relies on highly specific vegetation types in both breeding and wintering areas
• Area-sensitive: prefers to breed in habitat patches > 32 ha, in loose colonies near conspecifics
• Only able to raise a single brood per year, unlike many passerines
• Vulnerable to potential carry-over effects from poor conditions in non-breeding and migration areas

Rescue effect (from outside Canada)

Status of outside population(s) most likely to provide immigrants to Canada.

Stable to decreasing.

Population was stable to increasing in neighbouring parts of the U.S. over the past 30 years. However, declines have occurred since 2021 and are projected to continue in Michigan (20% to 50% over the next 10 years) due to habitat succession on managed lands.

Is immigration known or possible?

Yes.

Individuals known to disperse between the Lower and Upper Peninsulas of Michigan and between Michigan and Petawawa, Ontario, within and between breeding seasons. See Movements, Migration, and Dispersal.

Would immigrants be adapted to survive in Canada?

Yes.

The species’ habitat requirements are similar across the breeding range.

Is there sufficient habitat for immigrants in Canada?

Unknown.

Suitable habitat in Canada is currently limited. See Canada under Population Sizes and Trends.

Are conditions deteriorating in Canada?

Unknown.

Suitable habitat in Canada is limited; habitat succession at the primary site in Simcoe County also a potential limiting factor over the next 10 years, though this may be offset by restoration at nearby sites.

Are conditions for the source (that is, outside) population deteriorating?

Yes, partially.

Habitat management and cowbird control have led to increases over the past 10 to 15 years. However, declines have occurred since 2021 and are projected to continue in Michigan due to habitat succession on managed lands.

Is the Canadian population considered to be a sink?

Yes, probably.

Small, peripheral population. Although it has persisted since 2006, it has not grown in parallel with the core Michigan population, which increased over much of that time.

Is rescue from outside Canada likely, such that it could lead to a change in status?

No.

Immigration occurs, given presence of core population in nearby Michigan and species’ dispersal capabilities. however, suitable habitat in Canada is limited, and rescue is unlikely to change the species’ status.

Wildlife species with sensitive occurrence data (general caution for consideration)

Could release of certain occurrence data result in increased harm to the Wildlife Species or its habitat?

Yes.

II. Disturbance by observation

Detections of this species in Canada during the breeding season are suppressed by NHIC (Ontario), eBird and iNaturalist, so impact of recreational activities is currently negligible. However, there is a potential risk of breeding season disturbance and related population-level impacts due to observation by birders and photographers if details of nesting localities were publicized. In addition, the current primary nest sites have restricted access, and publishing the location of these may lead to trespassing (thus providing a potential disincentive for land managers to manage habitat for this species).

Status history

COSEWIC

Designated Endangered in April 1979. Status re-examined and confirmed in April 1999, May 2000, April 2008 and May 2024.

Status and reasons for designation

Status: Endangered

Alpha-numeric codes: D1

Reason for change in status: NA

Reasons for designation: The global breeding range of this colourful wood-warbler is restricted to large regenerating stands of even-aged Jack Pine and Red Pine in Michigan, and adjacent states and provinces. In Canada, it nests only in Simcoe and Renfrew Counties, Ontario, with additional breeding season observations in southwestern Ontario and Quebec’s Pontiac region. It primarily overwinters in the Bahamas. The global population is estimated at fewer than 5,000 birds, with only about 40-50 mature individuals currently occurring in Canada. Birds are limited by the availability of suitable nesting habitat, and threats include wildfire suppression resulting in loss of early-successional habitats; conversion of nesting and wintering habitat for agriculture, forestry, and human development; and impacts of climate change and increasingly severe weather throughout the annual cycle. In the absence of management initiatives forest succession may lead to loss of suitable breeding habitat in Canada, as is the case in the United States.

Applicability of criteria

A: Decline in total number of mature individuals

Not applicable.

There is no evidence of a reduction in the total number of mature individuals in the Canadian population.

B: Small range and decline or fluctuation

Not applicable.

Although the IAO of 56 km² is below the threshold for Endangered, the population is not severely fragmented and there is no evidence of continuing declines or extreme fluctuations.

C: Small and declining number of mature individuals

Not applicable.

There is no evidence of an observed, estimated or projected continuing decline in the number of mature individuals.

D: Very small or restricted population

Meets Endangered, D1.

The Canadian population is estimated to be < 250 mature individuals.

E: Quantitative analysis

Not applicable.

Analysis not conducted.

Preface

Kirtland’s Warbler was first designated as Endangered by COSEWIC in 1979. Its status was re-examined and confirmed in 1999, 2000 and 2008, based on COSEWIC update status reports. The most significant change to its conservation status since 2008 has been in the U.S. In 2019, Kirtland’s Warbler was removed from the U.S. Endangered Species List owing to sustained population increases since the 1990s, the stable availability of early-successional Jack Pine breeding habitat and the successful control of cowbird nest parasitism in the species’ core breeding range in the northern Lower Peninsula of Michigan (USFWS 2019). Notably, the primary objective in the U.S. recovery plan of a self-sustaining population of at least 1,000 pairs has been exceeded annually since 2001 (USFWS 2019), although declines have occurred since 2021 and are projected to continue (MDNR 2021; Mensing pers. comm. 2023). Since 2006, a small population has become established in Canada, and regularly breeds there. Current approaches to habitat management at the three breeding localities may result in future declines, though this could be offset by species-specific habitat management at other nearby sites.

COSEWIC history

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species.

Definitions (2024)

Wildlife Species

A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years.

Extinct (X)

A wildlife species that no longer exists.

Extirpated (XT)

A wildlife species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)

A wildlife species facing imminent extirpation or extinction.

Threatened (T)

A wildlife species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)^*

A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats.

Not at Risk (NAR)^**

A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.

Data Deficient (DD)^***

A category that applies when the available information is insufficient (a) to resolve a species’ eligibility for assessment or (b) to permit an assessment of the species’ risk of extinction.

*     Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.

**   Formerly described as “Not In Any Category”, or “No Designation Required.”

*** Formerly described as “Indeterminate” from 1994 to 1999 or “ISIBD” (insufficient scientific information on which to base a designation) prior to 1994. Definition of the (DD) category revised in 2006.

The Canadian Wildlife Service, Environment and Climate Change Canada, provides full administrative and financial support to the COSEWIC Secretariat.

Wildlife species description and significance

Name and classification

Current classification

Class: Aves

Order: Passeriformes

Family: Parulidae

Genus: Setophaga

Species: kirtlandii

Taxonomic changes since previous report:

Kirtland’s Warbler was classified in the genus Setophaga in 2011 along with the other former Dendroica warblers, based on the most recent phylogeny of the family Parulidae (Lovette et al. 2010; Chesser et al. 2011). The species’ closest relatives are Hooded Warbler (S. citrina), American Redstart (S. ruticilla), Cape May Warbler (S. tigrina), Cerulean Warbler (S. cerulea), Northern Parula (S. americana) and Tropical Parula (S. pitiayumi; Lovette et al. 2010). Widespread hybridization is not documented in the species, although one possible hybrid with Blackburnian Warbler (S. fusca) was reported in the Dominican Republic in 1997 (Latta and Parkes 2001).

Common names

English: Kirtland’s Warbler

French: Paruline de Kirtland

Description of wildlife species

Kirtland’s Warbler is a relatively large member of the Parulidae, weighing about 14 g (Bocetti et al. 2020). Adult males in breeding plumage have bluish-grey upperparts, a broken white eye-ring, black lores, a lemon-yellow throat and belly, and black streaks on the flanks and sides. Females and juveniles are similar to males but their plumage is duller, with lighter grey to brown upperparts, less black on the face, a paler yellow belly, and finer, less distinct breast streaks. Kirtland’s Warbler shares its habit of tail-bobbing with the Prairie Warbler (S. discolor) and Palm Warbler (S. palmarum). Its overall plumage pattern is similar to that of the Magnolia Warbler (S. magnolia), but the latter is smaller, has more prominent wing bars and tail markings, and does not bob its tail (Stephenson and Whittle 2013; Bocetti et al. 2020).

Designatable units

There are no known morphological or genetic distinctions within the population that would warrant consideration of additional designatable units. Thus, this report deals with a single designatable unit, Setophaga kirtlandii.

Special significance

Kirtland’s Warbler has a very small range distribution and is listed globally as Near Threatened by the IUCN. It is the only bird species in North America to depend exclusively on early-successional Jack Pine (Pinus banksiana) and Red Pine (P. resinosa) forests for breeding. The pine barren ecosystem that it relies on also supports other regionally rare wildlife and plant species in southern Ontario and Michigan (Corace et al. 2010; Burke 2018).

Aboriginal (Indigenous) knowledge

Aboriginal Traditional Knowledge (ATK) is relationship-based. It involves information on ecological relationships between humans and their environment, including characteristics of species, habitats and locations. Laws and protocols for human relationships with the environment are passed on through teachings and stories, and Indigenous languages, and can be based on long-term observations. Place names provide information about harvesting areas, ecological processes, spiritual significance or the products of harvest. ATK can identify life history characteristics of a species or distinct differences between similar species.

Cultural significance to Indigenous Peoples

There is no species-specific ATK in the report. However, Kirtland’s Warbler is important to Indigenous Peoples who recognize the interrelationships of all species within the ecosystem.

Distribution

Global range

Kirtland’s Warbler breeds in Ontario, and possibly in Quebec, in Canada, as well as in Michigan and Wisconsin in the U.S., from May to October, and overwinters primarily in The Bahamas from October to April (Figure 1).

Figure 1. Breeding, migrating and non-breeding (wintering) ranges of Kirtland’s Warbler. Data for the breeding and non-breeding ranges were sourced from BirdLife International (2022) and Birds Canada (2022a), and for the migration range, from Figure 4 in Cooper et al. (2017). One male tracked by Cooper et al. (2017) wintered in Cuba, although that country has not previously been recognized as forming part of the species’ wintering range (Bocetti et al. 2020). Figure credit: Karen Chung.

Breeding

Most of the global Kirtland’s Warbler population breeds in Michigan, with a very small number of confirmed breeders in Ontario and Wisconsin. Over 98% of the Michigan population nests in a core area in five counties along the Au Sable River drainage in the northern part of Michigan’s Lower Peninsula (USFWS 2019). Singing males have also been observed regularly on Michigan’s Upper Peninsula since 1982, and nesting was first confirmed there in 1995. In addition, the species has been regularly observed in Wisconsin since 1988 (Probst et al. 2003). The first nest was found in that state in 2007 (Trick et al. 2008) and birds have since bred in three counties (see Abundance under Data Sources, Methodologies, and Uncertainties; USFWS 2019; Olah et al. 2022).

In Ontario, there have been confirmed or probable breeding records of Kirtland’s Warbler in three census divisions since 2006 (Cybulski 2022; Tuininga pers. comm. 2023; DND unpubl. data), as well as sporadic sightings of birds in suitable breeding habitat throughout the southern part of the province. Birds have been sighted in Quebec in the past decade during the breeding season, but there are no breeding records from that province (Table 1; Figure 2).

Table 1. Summary of confirmed Kirtland’s Warbler detections in suitable breeding habitat in Canada since 2006. The count of mature individuals is a conservative estimate using the minimum annual count per site. ND indicates no data available, but birds likely present based on site history; the symbol ‒ indicates no survey conducted; and * indicates partial survey of suitable habitat conducted. Note that detections prior to 2006 were sporadic, with none in the 2000s earlier than 2006. Sources: Tuininga pers. Comm. (2023); Birds Canada (2022a,b); DND (unpubl. cata).

Figure 2. Kirtland’s Warbler observations in suitable breeding habitat in Ontario and Quebec in 1945 to 2022. Current observations (circles) are from the 20-year period 2004 to 2023; historical observations (triangles) are those prior to 2004. Data from Birds Canada (2022a,b) and Robert pers. comm. (2022). Figure credit: Karen Chung.

Migration

Kirtland’s Warbler uses different migratory routes in spring and fall. During spring migration, birds have been documented to stop over in coastal Florida, Georgia, South Carolina and southwestern Ontario (with a maximum of 5 to 10 individuals per year reported in Ontario; Burrell pers. comm. 2024). During fall migration, birds pass through the northwestern mid-Atlantic states and coastal North and South Carolina (Cooper et al. 2017; Cooper pers. comm. 2023).

Wintering

Kirtland’s Warbler is a Neotropical-Nearctic migrant that overwinters almost exclusively in The Bahamas (Cooper et al. 2017, 2019a). Data from light-level geolocators, targeted surveys and eBird checklists suggest that 63 to 90% of Kirtland’s Warblers overwinter in the central Bahamas, with the remainder distributed across the western and eastern Bahamas, Turks and Caicos, and possibly central Cuba (Cooper et al. 2017, 2019a). Finally, extralimital records of Kirtland’s Warbler from the following countries likely represent vagrants or migrant birds: Dominican Republic (Faanes and Haney 1989), Mexico (state of Veracruz; Lane 1975), Bermuda (Amos 2005) and Jamaica (Weidensaul 2019).

Canadian range

Breeding records/core range

Less than 1% of the known Kirtland’s Warbler global population and range are in Canada. Breeding records are concentrated in two disjunct areas: Simcoe County in southern-central Ontario and Renfrew County in southeastern Ontario (Figure 2).

In Simcoe County, there is one historical report of a Kirtland’s Warbler pair feeding a fledgling in Oro Township near Midhurst in 1945 (Speirs 1984). The presence of multiple pairs has been confirmed at one or more sites in Simcoe County since 2013, and nesting was confirmed in 2013 and 2014 (Burke 2018; Burke and Tuininga pers. comm. 2023;). [Editorial note: A citation has been removed to protect precise location information. Please contact the COSEWIC Secretariat if you require this information.]

In Renfrew County, Kirtland’s Warbler has occurred annually since 2006 at Garrison Petawawa, including confirmed nesting in 2007 to 2012, 2016 and 2017 (Richard 2013a; Cybulski 2016, 2022). After 2018, nesting has been probable but not confirmed, as monitoring efforts at Petawawa have shifted to remote surveys with autonomous recording units (ARUs; Cybulski 2022). Kirtland’s Warbler has a long record of breeding season occurrence in this area: individuals likely bred in the vicinity of Petawawa in the 1800s and early 1900s, and there are records of detections of singing males in 1916, 1939, 1946, 1977 and 1978 (Richard 2010).

A single mated pair was observed in Parry Sound District (Henvey Inlet First Nation) in 2015, along with multiple singing males since 2014 (see following section).

Breeding season detections/observations

Kirtland’s Warbler has recently been observed or recorded by ARUs at several sites with potential nesting habitat in Ontario and Quebec.

In Ontario, 1 to 4 males have been detected most years since 2014 in the eastern Georgian Bay area of the Parry Sound District (Table 1; Burke 2018; Burke and Tuininga pers. comm. 2022, 2023). This includes observations at Henvey Inlet First Nation (2015 to 2019), including a mated pair in 2015, and at French River Provincial Park in 2023 (Table 1; Burke pers. comm. 2023). In addition, a singing male was detected on one ARU recording from 6 June 2012 near Elliot Lake in Algoma District, out of 38 ARUs deployed in the region from 2012 to 2015 (Table 1; Holmes et al. 2015; Burke 2016). There are two sites with Ontario Breeding Bird Atlas records, both in Simcoe County: one singing male was detected in the county in 1985, and 5 to 6 males were detected in 2022 and one male was detected in 2023 at a Red Pine–Oak restoration site in Packard Tract, near Barrie (further habitat restoration is underway elsewhere in the county; Birds Canada 2022a; Burke and Tuininga pers. comm. 2022, 2023).

In Quebec, one male and one female Kirtland’s Warbler were observed in 2016, between 8 and 13 July, at Lac Rogecourt in the Pontiac Regional County Municipality. The area was searched again in June 2017, but no birds were detected (Boivin 2017). In recent years (2021 and 2022), the Canadian Wildlife Service (CWS) has deployed ARUs at sites with suitable Kirtland’s Warbler habitat at Bristol Mines, Île-du-Grand-Calumet and Cayamant in western Quebec. At least two males have been detected at two of these sites, and the potential exists to survey additional sites using ARUs (Robert pers. comm. 2022). See Canada under Data Sources, Methodologies, and Uncertainties.

Other detections/observations

Low numbers of Kirtland’s Warbler have been observed annually during migration in southwestern Ontario since the mid-1990s, based on observations entered in eBird, with most sightings occurring in the spring and a maximum of 5 to 10 individuals per year reported (Birds Canada 2022b; Burrell pers. comm. 2024; see Migration under Global range, above). Migration records have a bias towards well-visited birding hotspots (which are reflective of the only remaining forested habitat in extreme southwestern Ontario; Burrell pers. comm. 2024). A recent tracking study of migrating male Kirtland’s Warblers suggests that “southern Ontario or the northwestern Mid-Atlantic States” are an important spring stopover area (Cooper et al. 2017). Therefore, annual sightings in Point Pelee National Park on Lake Erie (Birds Canada 2022b; Dobbie pers. comm. 2023) may reflect its importance as a stopover site to some extent.

Population structure

No subspecies of Kirtland’s Warbler are recognized, and genetic diversity appears to be low and decreasing over the past century. Microsatellite locus genetic analyses comparing samples over a 100-year period found reduced genetic diversity over time, likely resulting from steep population declines and a resulting bottleneck effect from the 1940s to the 1970s (Wilson et al. 2012). Preliminary results from whole-genome analyses also suggest very high inbreeding levels in Kirtland’s Warbler, as indicated by the high number and length of runs of homozygosity (for example, Szpiech et al. 2013) compared to two closely related warbler species (Toews and Calderon pers. comm. 2023). The effects of low genetic diversity and high inbreeding on phenotypes are as yet unknown.

The migration and dispersal behaviours of Kirtland’s Warbler also appear to limit genetic divergence; see Movements, Migration, and Dispersal. Studies comparing the breeding and wintering sites of birds using resighting (n = 89) and geolocators (n = 27) showed no evidence of migratory connectivity, in which birds that breed at nearby sites also winter near one another (Cooper et al. 2017, 2018). Additionally, dispersal movements of 5 to 77 km by birds within a given breeding season, mainly by post-breeding or non-breeding birds (Probst et al. 2003; Cooper and Marra 2020; Cooper pers. comm. 2023), indicate the potential for range-wide population mixing.

Extent of occurrence and area of occupancy

The current extent of occurrence (EOO) in Canada is approximately 83,620 km² (Figure 3). A total of 14 sites were included in the EOO calculation, and each site met one of three criteria: (i) breeding season presence of Kirtland’s Warbler in multiple years during the 20-year period from 2004 to 2023 (n = 3; Table 1, also see Canadian range, above); (ii) at least one singing male observed in suitable habitat during at least one breeding season over that same period (n = 8; Table 1; Figures 2 and 3); or (iii) historical observations prior to 2004 at sites in Simcoe County, Bruce Peninsula and western Quebec with continuing suitable habitat (n = 3; Figures 2 and 3; Burke 2014, 2019; Robert pers. comm. 2022). Observations outside the breeding season or in habitat more suitable for migration (for example, Point Pelee National Park) were not included in the calculations.

Figure 3. Estimated extent of occurrence (EOO) of Kirtland’s Warbler in Canada as of 2023. Sites with breeding season occurrences or confirmed breeding in suitable habitat during the 20-year period from 2004 to 2023, and historical sites with continuing suitable habitat, were used to estimate the EOO. Note that, although 14 sites were used to define the EOO, precise coordinates were not available for two sites along northeastern Georgian Bay and they do not appear on this map. The latter sites are close [< 10 km] to the two Georgian Bay points appearing here and, as they are within EOO boundaries, their absence does not alter EOO calculations. Figure credit: Karen Chung.

The current index of area of occupancy (IAO) in Canada is approximately 56 km², using all the sites included in the EOO calculations. For the IAO, each site was assigned an area of 4 km², as most sites represent a single Kirtland’s Warbler observation or territory, and the two sites with multiple territories are both smaller than 4 km². The Department of National Defence (DND) estimated the area of suitable habitat at Petawawa to be 187 ha (1.87 km²) (Cybulski 2022). The primary Simcoe county site is estimated to be 132 ha (1.32 km²). [Editorial note: A citation has been removed to protect precise location information. Please contact the COSEWIC Secretariat if you require this information.]

Fluctuations and trends in distribution

The EOO and IAO were not calculated in the two previous Canadian status reports on Kirtland’s Warbler (COSEWIC 2000, 2008). However, neither metric appears to have declined since the last assessment in 2008. This assumption is based on the persistence of breeding birds at the two consistently occupied nesting locations, Petawawa (since 2006) and the primary Simcoe County site (since 2013), and an increase in the number of sightings of the species in Ontario and Quebec during the breeding season over the past 10‒15 years (see Canadian range, above).

Biology and habitat use

Life cycle and reproduction

Like most small songbirds, Kirtland’s Warbler begins breeding at one year of age (Bocetti et al. 2020). The approximate generation length is 2.2 years (Bird et al. 2020). The maximum lifespan recorded is 11 years for males and 8 years for females (Bocetti et al. 2020).

Kirtland’s Warbler is a ground-nesting species. Females build new nests annually near the base of a small pine or oak, often in the side of hummocks or furrows. Nests are constructed of grasses, sedges, pine needles, and leaves, and lined with mosses and animal hair (Mayfield 1960; Bocetti et al. 2020). Kirtland’s Warbler is territorial during the breeding season, and site fidelity is typically high in older, after-second-year (ASY) males and females as long as the habitat remains suitable in subsequent years (Bocetti et al. 2020).

Kirtland’s Warbler nests in loose colonies (that is, birds hold exclusive territories, but preferentially nest in the same habitat patch as conspecifics) and the social need for adjacent nesting pairs may limit numbers in some areas (Mayfield 1960). Broadcasts of male songs during the breeding season successfully attracted birds to restored sites in Wisconsin (Anich and Ward 2017) and Packard Tract in southern Ontario (Burke pers. comm. 2022).

Nest building is initiated soon after females arrive on the breeding grounds (range of female arrival in Michigan: May 11–June 18). Average lengths for each nest stage are building, 4 to 8 d; egg-laying, 3 to 6 d; incubation, 13 to 16 d; and nestling, 9 to 11 d. Fledglings may be attended by adults for 3 to 4 weeks (Mayfield 1960; Bocetti et al. 2020). Although Kirtland’s Warbler is mainly monogamous, up to 15% of males are polygynous. The species typically raises a single brood per year, or occasionally two for males arriving earlier on the breeding grounds (prior to approximately May 19: Rockwell 2013; Bocetti et al. 2020). The mean clutch size is 4.63 (range 3 to 6; Mayfield 1960; Bocetti et al. 2020). Fledging success rates vary depending on the severity of Brown-headed Cowbird (Molothrus ater) brood parasitism. Prior to cowbird control in the core range in Michigan, the parasitism rate was roughly 70%, and the average fledging success rate was less than 1 fledgling/nest (Walkinshaw 1972); after cowbird control, the latter increased to 2.98 fledglings/nest (average from four studies; Bocetti et al. 2020). Cowbird parasitism appears to be less of a threat in Canada, as there are few sightings of the species near Kirtland’s Warbler breeding sites. See Invasive and Other Problematic Species, Genes and Diseases under Threats. Predation by other bird species, mammals and snakes affects an estimated 15% of nests (Bocetti et al. 2020); see Interspecific interactions, below.

The overall annual adult survival rate is estimated to be 58 to 65% (Mayfield et al. 1960; Rockwell et al. 2017; Bocetti et al. 2020). A recent study of monthly survival rates in adult male Kirtland’s Warblers highlighted two key factors influencing survival: (i) migration mortality, which was estimated to account for 44% of total annual mortality; and (ii) March rainfall in The Bahamas, which was positively correlated with annual survival (Rockwell et al. 2017). Higher March rainfall is linked to greater food (fruit and arthropod) abundance, at a time when birds are fuelling up to prepare for spring migration in late March and April (Wunderle et al. 2010; Rockwell et al. 2017).

Habitat requirements

Breeding habitat

Kirtland’s Warbler is a habitat specialist, occurring primarily in early-successional Jack Pine or Red Pine forests. Until the mid-1990s, most sites occupied by the species had regenerated naturally after wildfires (Probst and Weinrich 1993; Donner et al. 2008). Today, most Kirtland’s Warblers in northern Lower Michigan, the core of the species’ range, nest in Jack Pine plantations specifically managed for the species (USFWS 2019).

Breeding habitat characteristics

Breeding Kirtland’s Warblers occupy Jack Pine forests 5 to 23 years old with 1.4 to 5.0 m tall trees (Probst and Weinrich 1993; Donner et al. 2008), typically with well-drained, sandy soils (Kashian et al. 2003). In Michigan, the highest occupancy is generally observed in areas with 2.4 to 3.8 m tall trees, moderate canopy cover (35 to 65%), and high stem densities (5,000 to 7,500 stems/ha; Probst and Weinrich 1993). The species also appears to be area-sensitive, preferring patches larger than 32 ha (Probst and Weinrich 1993), although patches of 12 to 32 ha are also used if adjacent to larger patches of suitable habitat (Donner et al. 2008). Although warblers may persist longer in larger habitat patches (Donner et al. 2010), densities can be high in both large (> 150 ha) and small (< 40 ha) patches, if other habitat features (for example, tree age) are suitable (Donner et al. 2009).

Kirtland’s Warbler will begin to occupy sites with roughly 1.5 m tall trees, 15 to 20% canopy cover and stem densities of 3,000 stems/ha. Bird density begins to decline once tree height exceeds 4.0 m and canopy cover is greater than 60%. Uniformly dense canopy cover is suboptimal, due to shading of the understory shrubs that provide food resources and shelter for nests (Probst and Weinrich 1993; Probst and Donnerwright 2003).

Mixed Jack Pine–Red Pine and Red Pine-dominated forests are also used by Kirtland’s Warbler in Ontario (Richard 2010, 2013a) and Wisconsin (Anich et al. 2011; Olah et al. 2022). In Wisconsin, a recent study found that the reproductive success of Kirtland’s Warbler in Red Pine-dominated plantations with stem densities of greater than 2,000 stems/ha was comparable to that in Michigan’s denser Jack Pine-dominated habitat, if other habitat features including ground cover were suitable (Olah et al. 2022). At Petawawa and Simcoe County in Ontario, Kirtland’s Warbler will also occupy territories with a White Pine (P. strobus) component of up to 20% (Richard 2010, 2013a; DND unpubl. data).

Nesting microhabitat

Kirtland’s Warbler nests on the ground on well-drained, typically sandy soils in the presence of the following plant species: Pin Oak (Quercus palustris), Low-bush Blueberry (Vaccinium angustifolium), Bearberry (Arctostaphylos uva-ursi), Bracken Fern (Pteridium aquilinum), Sand Cherry (Prunus pumila), Sweet Fern (Comptonia peregrina), bluestem grasses (Andropogon spp.) and sedges (Carex spp.; Probst and Donnerwright 2003; Bocetti et al. 2020). At Petawawa, blueberry (Vaccinium spp.), Coral Lichen (Cladonia stellaris), Reindeer Lichen (Cladonia rangiferina), and Wavy-leaved Moss (Dicranum polysetum) are the dominant ground cover species in Kirtland’s Warbler territories (Richard 2013b).

Current management

At Garrison Petawawa in Ontario, wildfires produced by lightning and military exercises periodically create new Kirtland’s Warbler habitat (see also Historical, long-term, and Continuing habitat trends), and the area of suitable habitat may be further enhanced by recent policies to reseed burned areas with Red Pine or a mix of Jack Pine and Red Pine (Richard 2013a,b).

In northern Michigan, Kirtland’s Warbler habitat is managed on 88,788 ha of federal and state-owned lands (as of 2019). Current practices include a Jack Pine planting regime tailored to the species’ preferred tree density and territory size, with harvesting and replanting at a stand age of 45 to 50 years (USFWS 2019). Management guidelines allow for up to 25% non-traditional practices, such as planting a mix of Jack Pine and Red Pine and planting at varying stem densities (USFWS 2019; Mensing pers. comm. 2023).

In Adams County, Wisconsin, experimental planting regimes initiated in 2013 on 145 ha of private land included mixed Jack Pine–Red Pine and Red Pine-only treatments, both of which successfully attracted males beginning in 2020 (Lopez pers. comm. 2022).

Migration habitat

Kirtland’s Warbler is rarely observed during migration. Most sightings have been along the western Lake Erie shoreline, in Ohio and Ontario (Clench 1973; Petrucha et al. 2013). The majority of sightings (82%) in both spring and fall migration have involved scrub habitat (shrubs < 6 m in height), with other sightings in residential areas, parks, woodlands, open habitats and orchards (Petrucha et al. 2013).

Winter habitat

Kirtland’s Warbler overwinters primarily in early-successional broadleaf scrub habitat with well-drained soils in The Bahamas (Sykes and Clench 1998; Wunderle et al. 2010; Cooper et al. 2019a). Although some early studies reported that the species occupied Caribbean Pine (P. caribaea) forests (Haney et al. 1998), it is in fact rarely found in pine-dominated habitat or mature forest during the winter, as these habitats typically lack the understory shrubs that provide food for the species (Cooper et al. 2019a).

Key habitat features distinguishing occupied wintering sites from unoccupied ones include a 3 to 28 year interval since human disturbance, an average canopy height of 1.8 m, and the highest foliage density in the 0.5 to 1.0 m height range (Wunderle et al. 2010). Food availability throughout the winter is an important indicator of habitat quality, especially the presence of three preferred food shrubs: Wild Sage or Lantana (Lantana involucrata), Black Torch (Erithalis fruticosa), and West Indian Snowberry (Chiococca alba; Wunderle et al. 2010).

Movements, migration, and dispersal

Migration

Kirtland’s Warbler is a complete migrant that winters in The Bahamas (Bocetti et al. 2020); see Wintering under Global range. Recent geolocator studies suggest that most birds perform a loop migration, using different spring and fall migration routes (Cooper et al. 2017).

During spring migration, most birds depart the wintering grounds in late April and early May, and arrive on the breeding grounds 16 days later on average (Ewert et al. 2012; Rockwell et al. 2012; Cooper et al. 2017). Birds largely follow a western route, flying northwards after making landfall in Florida. Important spring stopover sites inferred by light-level geolocators include coastal Florida, Georgia and South Carolina; and the portions of Ohio and southwestern Ontario adjacent to Lake Erie (Cooper et al. 2017). Drier late winter conditions in The Bahamas appear to delay arrival on the breeding grounds, particularly for first-year males, which often results in reduced nesting and fledging success for these individuals (Rockwell et al. 2012).

During fall migration, most birds depart the breeding grounds from mid-September through October, arriving on the wintering grounds around 18 days later. Most birds follow an eastern route, stopping over first at key sites in the northwestern mid-Atlantic states and then in coastal North and South Carolina (Cooper et al. 2017; Cooper pers. comm. 2023). It should be noted that, although Cooper et al. (2017) reported fall stopovers in southern Ontario based on light-level geolocator data, these records are now considered incorrect, as the geolocator data were over-interpreted for longitude, and recent Motus data provide no evidence of fall stopovers in Ontario (Cooper pers. comm. 2023).

Dispersal

Kirtland’s Warbler is a territorial species that exhibits site fidelity on both the breeding and wintering grounds (Wunderle et al. 2014). Site fidelity in winter varies (average 43%, range 11 to 67%) among individuals and appears to be linked to food resources. Individual warblers will shift their home ranges, especially in the late-winter dry period, to sites with a greater abundance of arthropods and ripe fruit (Wunderle et al. 2014). Individual birds are known to disperse over long distances both within and between breeding seasons (Probst et al. 2003; Cooper and Marra 2020; Cooper pers. comm. 2023), as well as when overwintering (Wunderle et al. 2014). First-year breeders have been shown to select potential breeding sites up to 350 km away from their natal sites, and banded individuals have dispersed from Lower to Upper Michigan to colonize new sites (Probst et al. 2003). Unpublished Motus tracking data demonstrate that individual birds can appear in Canada while en route to Michigan in May, or in rare cases, travel to different areas within Canada throughout the breeding season (Cooper pers. comm. 2023).

Interspecific interactions

Diet

Kirtland’s Warbler is omnivorous throughout the year, feeding primarily on fruit and arthropods (mainly insects). On the breeding grounds, important food items include blueberries; spittlebugs and aphids (Homoptera); ants and wasps (Hymenoptera); beetles (Coleoptera); and moth larvae (Lepidoptera; Deloria-Sheffield et al. 2001).

On the wintering grounds, the species’ diet consists approximately of 70% fruit and 30% arthropods, and it occasionally probes flowers for nectar (< 1% of foraging observations; Wunderle et al. 2010, 2014). Key fruits consumed include Wild Sage or Lantana, Black Torch and West Indian Snowberry (Wunderle et al. 2010). Food availability in late winter is critical for the warblers to store energy prior to migration, yet food resources are often limited in The Bahamas during this time owing to seasonal dry conditions.

Predators and competitors

Although predation of adult Kirtland’s Warblers has not been recorded, circumstantial evidence suggests that Sharp-shinned Hawk (Accipiter striatus), Northern Harrier (Circus hudsonius), Great Horned Owl (Bubo virginianus) and domestic cats (Felis catus) prey on adults (Bocetti et al. 2020). Eggs and young may be taken by American Crow (Corvus brachyrhynchos), Blue Jay (Cyanocitta cristata), Thirteen-lined Ground Squirrel (Ictidomys tridecemlineatus), North American Red Squirrel (Tamiasciurus hudsonicus), Common Raccoons (Procyon lotor), Striped Skunk (Mephitis mephitis), domestic cats and garter snakes (Thamnophis spp.; Mayfield 1960; Walkinshaw 1972; Bocetti et al. 2020). Cowbirds also destroy warbler eggs and chicks when parasitizing nests (Mayfield 1960).

Host/parasite/disease interactions

Relatively few bird species use young Jack Pine forests (Corace et al. 2010), and interspecific interactions such as nest-site competition have not been documented in Kirtland’s Warbler. Brood parasitism of Kirtland’s Warbler by Brown-headed Cowbird is a major threat to the species’ population (USFWS 2019). Cowbird control efforts implemented since 1972 have been successful at improving the warbler’s reproductive success in Michigan (Kelly and DeCapita 1982; Cooper et al. 2019b; Margenau et al. 2022); see Life cycle and reproduction. In Adams County, Wisconsin, cowbird control has had more limited success, perhaps because cowbirds are abundant in the agricultural lands adjacent to warbler habitat (Olah et al. 2022).

Physiological, behavioural, and other adaptations

Physiology

There is no information on the physiology of this species that pertains to the assessment of its conservation status.

Behaviour

Recently, Kirtland’s Warbler has shown some adaptability in inhabiting Red Pine or mixed Jack Pine–Red Pine habitat in Ontario and Wisconsin and in occupying cooler and wetter Canadian Shield habitat in northern Ontario (Richard 2013b; Olah et al. 2022; Burke and Tuininga pers. comm. 2022, 2023).

On the wintering grounds, the warbler also occupies early-successional habitats, which are vulnerable to predicted climate change impacts, including rising sea levels, increased winter temperatures and decreased late winter precipitation in The Bahamas (Wolcott et al. 2018); see Climate Change and Severe Weather under Threats. If birds become restricted to poor-quality wintering habitat with limited food resources prior to migration, carry-over effects may result in decreased breeding success (Rockwell et al. 2012) and adult survival (Rockwell et al. 2017).

Limiting factors

Kirtland’s Warbler is an early-successional habitat specialist that relies on specific vegetation types on both its breeding and wintering grounds. It is also area-sensitive in regard to nesting site selection, and preferentially nests in loose colonies near conspecifics; see Life cycle and reproduction, and Breeding habitat and Winter habitat under Habitat requirements. It typically raises only one brood per year (Rockwell 2013; Bocetti et al. 2020), which increases its sensitivity to brood parasitism by the Brown-headed Cowbird (Mayfield 1960) and to potential carry-over effects due to poor weather conditions in its wintering and migration areas (Rockwell et al. 2012).

Population sizes and trends

Data sources, methodologies, and uncertainties

Canada

In Canada, Kirtland’s Warbler sightings have been submitted primarily through eBird, especially during spring migration (Birds Canada 2022b). Although these records tend to be geographically biased towards areas that are heavily visited by wildlife enthusiasts, these areas are mainly national and provincial parks comprising much of the remaining suitable habitat for migrating songbirds in southwestern Ontario (for example, Point Pelee National Park).

In Ontario, CWS and the Ontario Ministry of Natural Resources and Forestry (OMNRF) have conducted species-specific Kirtland’s Warbler surveys since 1977 (Aird 2018). Between 2005 and 2016, annual targeted searches focused on areas with active forestry in the Chapleau, Sault Ste. Marie, Sudbury, Kirkland Lake and North Bay districts, and on Manitoulin Island. Jack Pine stands of 5 to 20 years were surveyed and identified based on GIS layers from the OMNRF Forest Resources Inventory (Burke 2014). However, no detections occurred during these surveys (Aird 2007, 2009, 2010, 2011, 2016; Burke 2014). Survey efforts are now focusing on Simcoe County, the Bruce Peninsula, the Georgian Bay Jack Pine barrens and the north shore of Lake Huron, based on habitat characteristics that more closely resemble those at some Michigan sites (for example, sandy soils, patch size > 30 ha) and on recent detections of territorial males (Burke 2014, 2019). Nevertheless, suitable habitat appears to be limited, with the exception of sites burned by wildfires, due to the lack of forestry practices conducive to the creation of Kirtland’s Warbler habitat (Burke pers. comm. 2023).

At Garrison Petawawa, survey methods have included broadcast surveys (that is, using song playback) in 2002 and from 2004 to 2012 (birds were detected each year from 2006 to 2012); a combination of broadcast surveys and ARUs from 2013 to 2018; and ARUs only since 2019 (Richard 2010; Cybulski 2022). Despite differences in the type of data available using these two methods (for example, females vocalize much less and may not be detected on ARU recordings), the number of singing males detected is thought to accurately represent the number of males (but not breeding pairs) on the base, as most of the known suitable habitat has been surveyed each year (Cybulski 2022). In Simcoe County, Kirtland’s Warbler has been observed since 2013, although presence-absence surveys have not been conducted annually at the primary site (Table 1). At Henvey Inlet First Nation in Parry Sound District, Kirtland’s Warbler was first detected opportunistically in 2015, and monitoring of the site has continued annually in conjunction with wildlife monitoring for a nearby wind energy development project (Burke 2016, 2018, 2019).

In Quebec, CWS conducted targeted surveys in 2007 in Kazabazua, Île-du-Grand-Calumet and Parc de la Vérendrye, and on Île aux Allumettes, but did not detect any Kirtland's Warblers. Furthermore, potential habitat identified from forestry maps did not appear to be suitable when ground-truthed (COSEWIC 2008). Since 2021, CWS has transitioned to using ARU monitoring of some potential Kirtland’s Warbler habitat in western Quebec, and this may be expanded to other suitable habitat in the future (Robert pers. comm. 2022). In 2021 (n = 3 ARUs deployed), one male was detected on a single day in mid-June at Île-du-Grand-Calumet. In 2022 (n = 14 ARUs), male songs were detected on two adjacent ARUs on multiple days in May-June 2022 at Cayamant. These two ARUs may have recorded the same individual, however, due to the close proximity (about 200 m apart) of the recorders (Robert pers. comm. 2022).

U.S.

The most comprehensive source of information on the global Kirtland’s Warbler population is the June census of singing males conducted in northern Michigan, where over 95% of the species’ population breeds (Figure 4). Full range-wide censuses took place in 1951, 1961, 1971 through 2013, 2015 and 2021, and partial censuses in 2017, 2019 and 2023 (USFWS 2019; MDNR 2021; Mensing pers. comm. 2023). Given that the census only counts singing males, but not females or nests, it overestimates abundance, as male pairing success is not 100%, but reportedly varies from 60% to 95% (average of 85%) depending on habitat quality (Probst and Hayes 1987). Nevertheless, the census provides standardized data on trends and habitat occupancy since the 1950s for most of the global population (USFWS 2019).

Figure 4. Annual count of singing male Kirtland’s Warblers in Michigan, based on full censuses conducted from 1951 to 2021 (USFWS 2019; MDNR 2021). Gaps indicate years when no census or a partial census was completed. Figure credit: Alana Demko.

In Wisconsin, the Department of Natural Resources (WDNR) has conducted an annual Kirtland’s Warbler census since 2008 in six counties with suitable habitat, following the Michigan protocol (Lopez pers. comm. 2022). Potential census sites are identified based on previous detections, species occupancy, Breeding Bird Atlas records and reports from volunteer observers. A subset of sites with the most suitable stand age and vegetation composition is then surveyed (Lopez pers. comm. 2022). Therefore, the Wisconsin census numbers can be considered a conservative estimate of the total number of birds in the state, as much, but not all, of the suitable habitat is surveyed annually. As with the Michigan census, only singing males are counted, so the count totals may overestimate abundance.

Abundance

Canada

The current size of the Kirtland’s Warbler population in Canada is estimated to be 40 to 50 mature individuals, based on the available numbers at sites with confirmed observations (Table 1). Garrison Petawawa has reported 1 to 5 singing males/year from 2006 to 2022 and 1 to 2 nests/year from 2007 to 2012 and from 2016 to 2017 (no nests were recorded from 2013 to 2015, and from 2018 to 2022; Richard 2013a; Cybulski 2016, 2022). Nest detection is likely influenced by changing survey methods; see Data Sources, Methodologies, and Uncertainties. Furthermore, the estimated population size is based on detections of singing males, whose pairing success varies depending on habitat quality (see U.S. under Data Sources, Methodologies, and Uncertainties). Therefore, the number of breeding pairs is less than the number of singing males.

At the primary site in Simcoe County, territorial pairs have been observed since 2013, and nests were found in 2013 and 2014. The probability of current nesting occurring there is high, given the annual detection of the species and continued availability of suitable habitat (Tuininga pers. comm. 2022); see Data Sources, Methodologies, and Uncertainties. The number of breeding birds was estimated at 22 singing males and 4 females in 2021; 27 males and 5 females in 2022; and 16 males and 3 females in 2023 (Burke 2018; Tuininga pers. comm. 2022). [Editorial note: A citation has been removed to protect precise location information. Please contact the COSEWIC Secretariat if you require this information.] However, these numbers may be incomplete due to the absence of a systematic survey and nest monitoring program for Kirtland’s Warbler at the site (Burke and Tuininga pers. comm. 2023).

Along northeastern Georgian Bay, 1 to 2 males were observed annually at Henvey Inlet from 2015 to 2019, and single males were also observed at other sites in the nearby Georgian Bay Biosphere Reserve and French River Provincial Park in Parry Sound District between 2014 and 2018, and in 2023 (Burke 2018; Burke and Tuininga pers. comm. 2022, 2023; Table 1). At Packard Tract in Simcoe County, where habitat restoration efforts began in 2017, 5 to 6 singing males were detected in 2022 and a single male in 2023 (Burke and Tuininga pers. comm. 2022, 2023).

In western Quebec, at least three male and one female Kirtland’s Warblers have been detected in potentially suitable breeding habitat since 2016, although no individuals have been confirmed over multiple years at the same site (Robert pers. comm. 2022).

U.S.

The 2021 Michigan Kirtland’s Warbler census reported 2,245 singing males (MDNR 2021; down from 2,383 in the 2015 census; see Population fluctuations under Fluctuations and trends). A partial census in 2023 in the core range showed a population decline in the past two years, with range-wide estimates now at fewer than 2,000 singing males (Mensing pers. comm. 2023). The total Michigan population is therefore estimated at 3,817 to 4,490 individuals, with the lower number based on an average pairing success of 85%, as reported by Probst and Hayes (1987) for this species, and the upper number assuming 100% pairing success. This number is a relatively accurate estimate of the global population, as over 95% of the species is known to breed in Michigan (USFWS 2019).

The Wisconsin population is small but persistent, growing from 9 singing males in two counties in 2008 to 32 males in four counties in 2022 (Lopez pers. comm. 2022). Over 25 singing males have been reported annually across six counties since 2016. Since 2007, nesting has been confirmed in three counties in multiple years (USFWS 2019; Olah et al. 2022).

Fluctuations and trends

Population fluctuations

There is no long-term information on population trends for Kirtland’s Warbler in Canada. Singing males have been detected sporadically, albeit in small numbers, at Garrison Petawawa since 1916, and breeding individuals have persisted at Petawawa since 2006 and at the primary site in Simcoe County since 2013 (Cybulski 2016; Burke 2018; DND unpubl. data). The species has also been observed regularly during spring migration in southwestern Ontario since the 1990s, an area that is also a stopover site for birds breeding in the U.S. (Cooper et al. 2017; Birds Canada 2022b).

The Michigan census provides a robust measure of the species’ global population size and trends over the past 70 years, given that consistent sampling protocols have been used and the entire known range of suitable breeding habitat in Michigan has been surveyed (USFWS 2019). The first full census in 1951 counted 432 singing males, and the 1961 survey found 502; however, a low of 167 males was reached in 1974 and 1987. The number of birds remained low from 1971 to 1986, despite aggressive cowbird control measures in almost all breeding areas after 1972 (Kelly and DeCapita 1982). Numbers began to increase once new Jack Pine habitat was created as a result of management measures and two large wildfires in 1975 and 1980 (Donner et al. 2008; Rapai 2012). Since the 1990s, the Michigan population has increased steadily with no large fluctuations, with a total of 2,383 singing males found in the 2015 census and 2,245 males, in the 2021 census (USFWS 2019; MDNR 2021; Figure 4). However, a more recent decline has been observed based on a partial census of singing males in Michigan in 2023, which included approximately 50% of the species’ core range in Michigan, and continued declines are predicted in the region over the next 10 years due to limited habitat availability (Mensing pers. comm. 2023); see Biological Resource Use and Human Intrusions and Disturbance under Threats; and Historical, Long-term, and Continuing Habitat trends. The small Wisconsin population has persisted since 2008 (Lopez pers. comm. 2022).

Long-term historical population trends

The limited historical sightings of Kirtland’s Warbler in Canada suggest that the species was always rare here, at least during the last 200 years. Individuals likely bred in the Petawawa area in the 1800s and early 1900s, and singing males were detected there in 1916, 1939, 1946, 1977 and 1978 (Richard 2010). However, until 2007, the only documented case of successful breeding in Canada was near Midhurst in Oro County (near Barrie, Ontario) in 1945 (Speirs 1984). Globally, the Kirtland’s Warbler population is believed to have been at a historical high in the late 1800s, when abundant wildfires in Michigan and the widespread clearing of land on both the breeding and wintering grounds promoted early-successional habitat growth beneficial for the species. Fire suppression policies used in forestry beginning in the 1900s, along with the increased threat of cowbird parasitism as forests were cleared and the cowbird’s range expanded, likely contributed to the substantial decline in Kirtland’s Warbler numbers between 1900 and 1950 (Mayfield 1960; USFWS 2019).

Severe fragmentation

Although over 50% of individuals in Canada occur in a habitat patch smaller than that required to support a viable subpopulation, these sites are all within dispersal distance of each other from the perspective of a migratory songbird; therefore, Kirtland’s Warbler does not meet COSEWIC’s definition of “severely fragmented.”

Rescue effect

Kirtland’s Warblers from Michigan or Wisconsin could breed in Canada, based on the documented dispersal behaviour of this species (Probst et al. 2003; Cooper and Marra 2020). Large distances and extensive areas of open water are not an apparent barrier, as at least six banded males from Lower Michigan have dispersed to Michigan’s Upper Peninsula, and regular movements have been observed between the two regions (Probst et al. 2003). Recent data from Motus tags also indicate that individual Kirtland’s Warblers regularly disperse over large distances within and between breeding seasons (Burke 2018; Cooper and Marra 2020; Cooper pers. comm. 2023).

Additionally, the core (source) population in northern Lower Michigan has steadily risen since the early 1990s, increasing the possibility of rescue (USFWS 2019). However, the availability of Kirtland’s Warbler habitat on state-managed lands there is expected to decrease over the next 10 years due to below-target harvesting and replanting efforts since 2011. This habitat loss is predicted to result in a 20 to 50% decline in the number of singing males in those areas, which could reduce the Michigan population to fewer than 1,000 singing males in the absence of other events creating new warbler habitat, such as large wildfires (Mensing pers. comm. 2023).

In southern Ontario, a recent GIS landscape analysis of soil and vegetation characteristics in 33 counties suggests that Kirtland’s Warbler habitat could potentially exist throughout the region (Burke 2018). However, the ground-truthing of the potential habitat in Simcoe and Dufferin counties identified in that analysis found that early-successional Red Pine–Oak cover is scarce, limiting the current availability of suitable habitat for immigrant birds (Burke 2018, 2019).

Collectively, this information suggests that the potential for rescue is limited, because the U.S. population remains small (and is now declining) and suitable breeding habitat in Canada is scarce. The Canadian population is likely a sink, given its small size, lack of apparent growth over the past decade despite an increase in the U.S. population over the same period (Table 1), and current forestry practices that are not conducive to the creation of Kirtland’s Warbler habitat.

Threats

Historical, long-term, and continuing habitat trends

Ontario and Quebec

No information is available on habitat trends for Kirtland’s Warbler in Canada, as the species has only occupied two sites (Petawawa and in Simcoe County) consistently since 2006 and 2013, respectively. Extensive Jack Pine habitat exists throughout much of Ontario and Quebec, and continues to be periodically cleared by fire and harvesting in northern regions of these two provinces. However, searches by CWS and OMNRF for Kirtland’s Warbler in six districts in northern Ontario between 2005 and 2016 failed to detect the species (Aird 2007, 2009, 2010, 2011, 2016; Burke 2014), suggesting that the habitat in these regions may be less suitable, despite historical detections of a single male in Kenora (August 1988) and another in the Sudbury area (June 1982).

Some areas of southern Ontario, particularly in Simcoe County and the Bruce Peninsula (Birds Canada 2022b), appear to potentially provide habitat with more suitable characteristics (Burke 2014) and are the focus of the current survey and habitat restoration efforts (Burke 2018, 2019). However, suitable habitat appears to be limited in these regions, due to high human population density and competing land-use interests such as agriculture and pine plantations (Burke 2018, 2019).

At Garrison Petawawa, fire has been an important factor in the creation of Kirtland’s Warbler habitat. In 2012, a wildfire created 204.4 ha of suitable habitat near currently occupied warbler territories (Richard and Cybulski 2013a). From 2013 to 2016, the warblers continued to occupy areas adjacent to the burn (Cybulski 2016), and shrub regrowth in the burned areas appeared to provide key food resources (for example, blueberries) for the warblers (Richard and Cybulski 2013b; Cybulski and Wilson 2014). Since 2019, this regenerating area has been the core habitat for Kirtland’s Warbler at Petawawa, and is predicted to remain suitable until 2033 (Cybulski 2022). At Henvey Inlet in the Parry Sound District, a similar situation has occurred post-fire, as Kirtland’s Warbler males were observed during the 2023 breeding season at regenerating Jack Pine habitat following a large 2018 wildfire (Burke 2019; Burke and Tuininga pers. comm. 2023); see Invasive and Other Problematic Species, Genes and Diseases under Threats.

U.S.

In the species’ core range in Michigan, habitat quantity and quality have been stable or have increased over the past 20 years. However, the availability of Kirtland’s Warbler habitat on managed lands is predicted to decrease over the next 10 years, due to below-target harvesting and replanting efforts, which could potentially reduce the number of singing males by 20 to 50% within the next decade (Mensing pers. comm. 2023). Stochastic events, including severe droughts and heat events (which may cause higher Jack Pine mortality), infestations by insects such as Jack Pine Budworm (Choristoneura pinus), and fungal infections could potentially reduce future habitat availability, whereas wildfires could increase habitat availability beginning 5 to 10 years post-fire (USFWS 2019).

The Bahamas

Habitat trends on the wintering grounds are also unknown. However, new habitat is often created by human disturbance (for example, brush fires, clearing and farming) and may be maintained over the long term in areas that are periodically cleared by activities such as goat grazing (Wunderle et al. 2010; Fleming et al. 2019).

Hurricanes in the Caribbean can reduce habitat on individual islands, as well as periodically create new habitat suitable for Kirtland’s Warbler. The overall impact of hurricanes on habitat creation is unpredictable, given the variable timing, extent and severity of these storms (Wunderle et al. 2007). Other weather-related effects in The Bahamas resulting from climate change—particularly rising sea levels, increased winter temperatures and decreased late winter precipitation—are predicted to impact habitat availability later this century; however, the extent of these effects is unknown (Wolcott et al. 2018). See Climate Change and Severe Weather under Threats.

Current and projected future threats

Kirtland’s Warbler is vulnerable to the cumulative effects of various threats, especially reduced breeding habitat quality owing to fire suppression; loss and fragmentation of breeding and wintering habitat due to agriculture, forestry and human development; and brood parasitism by the Brown-headed Cowbird. The nature, scope and severity of these threats are described in Appendix 1, following the IUCN-CMP (International Union for the Conservation of Nature–Conservation Measures Partnership) unified threats classification system (see Salafsky et al. 2008 for definitions and Master et al. 2012 for guidelines). The threat assessment process consists of assessing impacts for each of 11 main categories of threats and their subcategories, based on the scope (proportion of population exposed to the threat over the next 10-year period), severity (predicted population decline within the scope during the next 10 years or 3 generations, whichever is longer, up to approximately 100 years), and timing of each threat. The overall threat impact is calculated by taking into account the separate impacts of all the threat categories and can be adjusted by the species experts participating in the threats evaluation.

The overall threat impact for Kirtland’s Warbler is considered to be High–Medium, corresponding to an anticipated further decline of between 8% and 70% over the next ten years (Appendix 1). These values are to be interpreted with caution, as they may be based on subjective information such as expert opinion, although efforts have been made to corroborate the scores with available studies and quantitative data.

Agriculture and aquaculture (IUCN 2; medium–low threat impact)

2.1 Annual and perennial non-timber crops

In The Bahamas, much of the early-successional habitat suitable for overwintering Kirtland’s Warblers has no official legal protection, and is therefore under threat from land clearing for small-scale agriculture (USFWS 2019). Although new wintering habitat for the species is periodically created by human activities, including agriculture and brush fires, this habitat may also be altered (for example, reduced shrub species diversity) or destroyed when areas are cleared (Wunderle et al. 2010). The scope is rated as Restricted–Small, because much of the current habitat has already been altered by human activities and the species is adapted to early-successional habitats. The severity is rated as Moderate–Slight, because birds have the ability to disperse to nearby suitable habitat on the wintering grounds. However, some uncertainty exists over the future extent of habitat alteration, particularly at migration stopover sites (for example, human development in Florida).

2.2 Wood and pulp plantations

In the past, forestry activities resulted in the permanent conversion of Jack Pine barrens and Red Pine−Oak ecosystems to pine plantations, reducing the availability of suitable habitat for Kirtland’s Warbler in terms of both stand age and vegetation species composition (Mayfield 1960). In both Ontario and Michigan, the commercial forestry industry has focused on replanting harvested areas with pine monocultures, which typically have sparse ground cover, low tree stem densities and few openings with grasses and shrubs for foraging and nest protection (Burke 2018; Bocetti et al. 2020). The fragmentation and isolation of Jack Pine stands may also have contributed to historical decreases in Kirtland’s Warbler numbers (Probst and Weinrich 1993; Bocetti et al. 2020).

Many pine plantations and Christmas tree farms in southern Ontario provide suboptimal nesting habitat for Kirtland’s Warbler, due to the low vegetation species diversity, lack of understory shrubs, high canopy cover, dominance of non-native and hence less-preferred tree and shrub species (for example, Scots Pine, P. sylvestris), and stand age of over 20 years (Burke 2018). Plantations can provide suitable Kirtland’s Warbler habitat when native conifer species and understory vegetation are present, although management to maintain an optimal successional stage for the species to breed is an important consideration. At the primary site in Simcoe County, where roughly 50% of the Canadian population of Kirtland’s Warbler breeds, the core habitat consists of 132 ha of 8- to 20-year-old native Red and White Pine plantations. [Editorial note: A citation has been removed to protect precise location information. Please contact the COSEWIC Secretariat if you require this information.] Future habitat loss due to ageing trees and lack of a comprehensive habitat management plan for Kirtland’s Warbler at the site have been flagged as potential threats (Burke and Tuininga pers. comm. 2023). [Editorial note: A citation has been removed to protect precise location information. Please contact the COSEWIC Secretariat if you require this information.] The scope is rated Large, because the primary occupied breeding habitat in Simcoe County is likely to become unsuitable within 10 years and no habitat recovery initiatives for Kirtland’s Warbler are planned there. The severity is potentially Serious, due to the possible loss of most of the current breeding habitat at the primary Simcoe County site and some habitat at Petawawa. However, habitat restoration efforts specifically targeting the species’ requirements are occurring elsewhere in the area (for example, at the Packard and Museum tracts) and have successfully attracted Kirtland’s Warbler (Burke 2022; see Recovery Activities under Protection, Status, and Recovery Activities). As these habitat restoration efforts may result in a net gain of habitat, or at least offset losses at the primary Simcoe County locality (Burrell pers. comm. 2024), the severity is assessed as Moderate–Slight.

Natural system modifications (IUCN 7; medium–low threat impact)

7.1 Fire and fire suppression

Fires may displace birds in the short term (< 5 years post-fire). However, they may be beneficial 5 to 20 years post-fire, if some suitable habitat remains unburned, as fire is essential for Jack Pine germination. In Ontario, wildfires are continuing to create new Kirtland’s Warbler habitat on a local scale. Notably, a wildfire in 2012 burned over 200 ha of land adjacent to currently occupied Kirtland’s Warbler territories at Garrison Petawawa (Richard and Cybulski 2013a). Following a period of absence, this area of regenerating Jack Pine has been re-occupied by the warblers since 2019, including five males (the highest number yet observed at this site) in 2022 (Cybulski 2022). See Ontario and Quebec under Historical, Long-term, and Continuing Habitat trends. At Henvey Inlet, a 2018 wildfire burned over 100 km² of Jack Pine habitat, including an area occupied by Kirtland’s Warbler in the previous four years; see Extent of occurrence and area of occupancy. In 2023, four singing males were detected in regenerating habitat approximately 10 km from the previously occupied site (Burke and Tuininga pers. comm. 2023). The scope is rated Pervasive, as most of the breeding habitat was altered by fire in the previous decade or is at risk of fire in the next decade. Additionally, the warmer and drier summer conditions predicted over the next century due to climate change are likely to increase the frequency of wildfires across Canada and impede the post-fire regeneration of conifer species including Jack Pine (for example, Van Bogaert et al. 2015; Boucher et al. 2020). The severity is rated Moderate–Slight, given that birds are able to disperse to new breeding areas if their current territories are altered by fire.

7.3 Other ecosystem modifications

Historically, fire suppression has reduced the quality of Kirtland’s Warbler habitat in the species’ core range in Michigan. Prior to European settlement in the late 1800s, the supply of extensive patches of young Jack Pine was renewed on an ongoing basis by lightning-caused fires in the Michigan pine barrens (Mayfield 1960). These fires produced Jack Pine habitat of the appropriate successional stage, tree height, stem density and ground cover for breeding (Probst and Donnerwright 2003). However, fire suppression policies drastically reduced the extent and frequency of wildfires in this region. Indeed, the small Michigan Kirtland’s Warbler population expanded after extensive fires during the 1970s and 1980s (Probst and Weinrich 1993; Donner et al. 2008). The lack of management of the modified habitat occupied at the primary Simcoe County site, and its likely succession to habitat unsuitable for Kirtland’s Warbler, is addressed in Wood and Pulp Plantations, above.

On the wintering grounds, the aggressive spread of non-native plant species, including Jumbie Bean, Brazilian Pepper (Schinus terebinthifolius), Guinea Grass (Panicum maximum) and Casuarina (Casuarina equisetifolia), could potentially crowd out preferred native forage species in early-successional habitats, thus reducing habitat quality for Kirtland’s Warbler (USFWS 2019).

The scope is rated Pervasive, because most of the breeding habitat is under potential threat, especially from fire suppression. The severity is rated as Moderate–Slight, as birds are able to disperse to alternative breeding or wintering sites that have the preferred habitat characteristics (for example, native fruiting shrubs).

Human intrusions and disturbance (IUCN 6; low threat impact)

6.1 Recreational activities

Kirtland’s Warbler is less susceptible to human disturbance than many songbirds (Mayfield 1960). In Canada, the species’ current nesting sites include military land that is not publicly accessible. However, it is a highly sought-after species by birders and photographers, and breeding activities could be disrupted by large numbers of visitors to warbler territories during the nesting period and by the use of audio playback to attract birds for observation and photographs (Mayfield 1960). This can be minimized by preventative measures at known nesting sites. In Michigan, Kirtland’s Warbler birding tours are a popular form of ecotourism, and access to breeding sites is restricted to a limited number of visitors at a time to avoid undue disturbance (Rapai 2012; Bocetti et al. 2020). At the Packard Tract restoration site in Simcoe County, Ontario, similar efforts are underway to promote outreach, while also reducing disturbance to breeding birds (Burke pers. comm. 2022). The scope is rated Small, because potential disturbance is limited to publicly accessible areas (for example, Parry Sound) where a minority of the species’ Canadian population is found. The severity is rated as Negligible due to presumed low levels of direct mortality from this threat, but if the population shifts to sites outside restricted-access military land, the severity becomes Unknown.

6.2 War, civil unrest and military exercises

In Ontario, a large portion of the consistently occupied breeding habitat is on active military land, with restricted public access, although illegal entry to observe the birds remains a concern (Richard 2013b; Burke and Tuininga pers. comm. 2022). Military training activities at installations in Canada could potentially impact Kirtland’s Warbler; however, human access is usually restricted in these areas, and no live-firing exercises are authorized in nesting areas during the breeding season (Richard 2013b). Despite these preventative measures, human activities may still be responsible for habitat loss (for example, 2012 wildfire at Petawawa; see Natural System Modifications under Threats). The scope is rated Pervasive, because a high proportion of the Canadian population breeds on active military land. The severity is rated Slight, as training exercises are restricted near active breeding sites, although the specific mitigation policies implemented are unknown, such as the radius of the buffer zones around warbler habitat during the nesting period.

6.3 Work and other activities

On the wintering grounds in The Bahamas, the majority of the habitat occupied by Kirtland’s Warbler does not have any official legal protection (see Legal protection and status), and the financial resources for habitat restoration and management are limited. This may hamper continued recovery efforts for the species (Ewert pers. comm. 2023). The scope is rated Pervasive, as the majority of the global Kirtland’s Warbler population winters in The Bahamas. The severity is rated as Slight, since the species is dispersed across multiple islands and habitat loss is therefore likely to be localized.

Invasive and other problematic species, genes and diseases (IUCN 8; low threat impact)

8.1 Invasive non-native/alien species/diseases

Throughout the species’ annual cycle, predation of both adults and nestlings by domestic and feral cats is a potential threat; see Predators and competitors under Interspecific interactions. The scope is rated as Pervasive, because cats are abundant at wintering and migration sites and at most breeding sites. The severity is rated as Slight; although mortality from cat attacks is high, these attacks are likely uncommon (that is, cause limited mortality) and adult survival in the species is reportedly high, especially on the breeding and wintering grounds (Rockwell et al. 2017).

8.2 Problematic native species/diseases

A major threat to Kirtland’s Warbler is brood parasitism by the Brown-headed Cowbird (Mayfield 1960; USFWS 2019). Owing to the cowbird’s relatively recent arrival (since approximately 1890; the species is originally from western North America) in the Kirtland’s Warbler range as a result of agricultural land clearing, the warblers have not had time to adapt to the threat by ejecting eggs or re-nesting (Mayfield 1961; Walkinshaw 1972). Cowbirds reduce warbler reproductive success by (i) removing warbler eggs and replacing them with cowbird eggs; (ii) reducing warbler hatching success, since the warbler eggs, which are smaller, receive less heat from incubation than the larger cowbird eggs; (iii) hatching earlier than warbler eggs, since cowbirds require a shorter incubation period than warblers; and (iv) reducing warbler fledging success, since cowbird nestlings are larger than their warbler nest mates and outcompete them for food.

In the 1960s and 1970s, roughly 70% of all Kirtland’s Warbler nests in Michigan were parasitized by cowbirds, producing an average of less than 1 fledgling/nest (Walkinshaw 1972). After cowbird control was implemented in 1972, the number of parasitized nests fell to less than 5% and the average number of fledglings/nest increased to a more sustainable level of 2.72 to 3.59 (Kelly and DeCapita 1982; Rockwell 2013; Bocetti et al. 2020). Although Kirtland’s Warbler has been de-listed in the U.S., funding for ongoing cowbird control is still available as needed through a Michigan Department of Natural Resources (MDNR) endowment fund (USFWS 2019). However, there is encouraging evidence that cowbird parasitism may become less of a threat to breeding Kirtland’s Warblers in the future. A recent study of cowbird parasitism of Kirtland’s Warbler nests in Michigan found that only 1.3% of nests were parasitized from 2018 to 2021, despite reduced cowbird trapping in the area from 2015 to 2017 and the halting of all trapping by 2018 (Cooper et al. 2019b; Margenau et al. 2022).

In southern Ontario, cowbirds are common and thus pose a potential threat to Kirtland’s Warbler in Canada, but recent Breeding Bird Survey trends show statistically significant long-term and short-term declines in cowbird populations in the province (Smith et al. 2020). At Petawawa, cowbirds are reportedly uncommon (Richard 2013b). Indeed, no cowbirds were detected during Kirtland’s Warbler broadcast surveys and territory monitoring, and no nest parasitism has been documented there (Richard and Cybulski 2011, 2013a,b; Cybulski and Wilson 2014; Cybulski et al. 2015; Cybulski 2016). Cowbird abundance is also reportedly low at the Packard and Museum Tract restoration sites based on monitoring there since 2017 (Burke pers. comm. 2023).

The scope is rated Large because, although cowbird numbers are declining across Ontario and are low in the north (Petawawa), the species is present in southern Ontario. The severity is rated as Unknown, since cowbird abundance is unknown at key breeding sites such as Simcoe County.

Climate change and severe weather (IUCN 11; low threat impact)

11.1 Habitat shifting and alteration

On the breeding grounds, climate modelling predicts that mean annual temperatures in the Kirtland’s Warbler core range in Michigan will increase by 1.2 to 4.5 °C in the next 100 years, resulting in important shifts in vegetation community composition (Handler et al. 2014). This region is near the southern edge of the current Jack Pine range, and a roughly 75% reduction in Jack Pine occupancy is expected to occur across the Great Lakes region, including Ontario, as the range of this tree species shifts further north (Donner et al. 2018). Although habitat availability is predicted to be stable in areas currently occupied by Kirtland’s Warbler in northern Lower Michigan and Wisconsin, habitat loss through this mechanism is still a concern range-wide, including in southern Ontario and in Michigan’s Upper Peninsula (Donner et al. 2018; USFWS 2019). Conversely, given that the areas of Jack Pine occupancy in northern Ontario are cooler and wetter than the warbler’s current habitat further south (Tuininga pers. comm. 2023), future warming trends could result in the warblers shifting their distribution northwards. Over the next century, anticipated warmer temperatures on the breeding grounds due to climate change could also result in increased numbers of pest species such as Jack Pine Budworm (Handler et al. 2014; USFWS 2019).

On the wintering grounds, rising sea levels resulting from climate warming may reduce the available area of suitable habitat in The Bahamas. However, further habitat characterization using high-resolution imagery is needed to assess how much of the coastal habitat under threat is in fact suitable for Kirtland’s Warbler, and whether inland habitats could compensate for the loss of coastal areas (Wolcott et al. 2018). The scope is rated as Pervasive, as habitat alteration is expected to occur range-wide. The severity is considered Unknown over the next 10 years, although longer-term effects (50 to 100 years) could be Extreme.

11.2 Droughts

A recent analysis suggested that predicted higher winter temperatures and reduced late winter precipitation in The Bahamas, particularly on the central islands where the majority of the global population winters, could result in severe drought conditions later this century (Wolcott et al. 2018). Late-winter droughts could negatively impact Kirtland’s Warbler survival by reducing food availability. Higher March rainfall in The Bahamas is positively correlated with annual survival, since fruit and arthropods, which are important fuel for migration, are more abundant in wetter years, resulting in better body condition prior to migration and therefore better migratory survival (Wunderle et al. 2010; Rockwell et al. 2012, 2017). Although individual birds will adapt to dry late-winter conditions to some extent by shifting their home ranges to sites with greater food abundance (Wunderle et al. 2014), severe drought conditions may result in a reduction in or loss of these “oases” in the landscape. The scope is rated as Pervasive, since drought conditions could occur range-wide. The severity is considered Slight over the next 10 years, as birds could disperse to more suitable habitat within or between islands, although longer-term effects (50 to 100 years) could be Extreme if severe droughts persist over multiple years.

11.4 Storms and flooding

The frequency of extreme weather events is expected to increase over the next century due to climate change, with this occurring throughout the Kirtland’s Warbler annual cycle (USFWS 2019). The highest rate of mortality in adult Kirtland’s Warblers occurs during migration; therefore, more climate-change-induced weather events (for example, storms and extreme temperatures) during migration could reduce adult survival (Rockwell et al. 2017). Hurricanes in the Caribbean could reduce the availability of wintering habitat on a local (island-level) scale; however, hurricanes also create new early-successional habitat and tend to be localized to particular islands (Wunderle et al. 2007).

Increased overall precipitation, and more extreme annual peaks, are predicted in northern Michigan due to climate change, and similar conditions are expected in Kirtland’s Warbler breeding habitat in neighbouring Canada. Winters and springs are expected to be wetter, while summers are expected to be drier (Handler et al. 2014). In addition, an increase in extreme weather events (for example, heavy rain and snow) is predicted (Handler et al. 2014). These events could have various negative effects on Kirtland’s Warbler survival, including reduced food availability for the young during summer droughts, and mortality of both adults and young due to storms. Effects could vary regionally, given that Jack Pine-dominated areas of northern Ontario tend to be cooler and wetter on average than southern Ontario or Michigan (Tuininga pers. comm. 2023). The scope is rated as Pervasive, since weather events could occur range-wide. The severity is considered Slight over the next 10 years, as storms are local events and birds could disperse to nearby suitable habitat, although longer-term effects (50 to 100 years) could be Extreme.

Residential and commercial development (IUCN 1; unknown threat impact)

1.1 Housing and urban areas

Kirtland’s Warbler is a nocturnal migrant, and mortality may occur due to collisions with buildings and other lit structures during spring and fall migration, particularly in large cities along the Great Lakes. Five Kirtland’s Warbler deaths have been attributed to nighttime collisions: two with windows and three with lit human-made structures (for example, monuments; Mayfield 1960; USFWS 2019), and additional unreported mortalities are highly likely. The scope is rated as Pervasive, as most birds migrate through urban areas with high human population density and development. The severity is rated as Unknown because, although confirmed mortalities of the species due to collisions are few, many collisions likely go unreported. Urban development in Florida may also be reducing habitat at migratory stopover sites, but the scope and severity of this threat are Unknown.

Transportation and service corridors (IUCN 4; unknown threat impact)

4.1 Roads and railroads

Edge habitats such as those along roads and utility corridors may positively or negatively affect Kirtland’s Warbler. On the breeding grounds, edge habitat may benefit the species when foraging shrubs are present, and the birds often nest near openings or edges in their territory, including roads (Bocetti et al. 2020). However, the species is sensitive to fragmentation, as it prefers larger habitat patches for nesting (Probst and Weinrich 1993); see Breeding habitat under Habitat requirements. On the wintering grounds, utility corridors may provide suitable foraging areas if maintained at a suitable stage of succession by goat grazing or clearing (Wunderle et al. 2010; Fleming et al. 2019). Although there are occasional reports of Kirtland’s Warbler collisions with motor vehicles in the U.S., most of the breeding habitat is in less populated areas distant from major roadways (USFWS 2019). One Kirtland’s Warbler fatality by motor vehicle strike has been reported in The Bahamas (Ewert pers. comm. 2023). The scope is considered Pervasive, as the species is exposed to roads throughout its annual cycle. The severity is rated as Unknown, since the number of collisions is not well documented, especially during migration.

Biological resource use (IUCN 5; unknown threat impact)

5.3 Logging and wood harvesting

Although current forestry practices help to create Kirtland’s Warbler habitat in many areas, harvesting and logging may be detrimental to the species overall. In Ontario, habitat restoration efforts targeting the species mimic natural succession, incorporating the latest available information on species composition and cover (trees and shrubs), stand age and the preferred size of nesting areas (Richard 2013b; Burke 2018). However, commercial logging practices often allow natural succession to occur for longer than 20 years, or promote replanting with tree species less suitable for nesting warblers (Tuininga pers. comm. 2023). In Michigan, forestry practices on MDNR lands over the past 30 years have been beneficial to the species, including a 45 to 50 year rotation regime (that is, harvesting and replanting cycle) for Jack Pine (Corace et al. 2010; USFWS 2019). However, these forestry practices are not legally binding and, therefore, habitat availability for Kirtland’s Warbler on MDNR lands is predicted to decrease over the next 10 years due to below-target harvesting and replanting efforts in the past decade (Mensing pers. comm. 2023). This habitat loss is predicted to result in a 20 to 50% decline in the number of singing males in those areas; see Rescue effect. The scope is rated as Pervasive, because most of the breeding habitat in Canada could disappear within 10 years without adaptive management. The severity is rated as Unknown, as the overall impact depends on whether harvesting occurs at those sites within the next decade.

Pollution (IUCN 9; unknown threat impact)

9.3 Agricultural and forestry effluents

Throughout its annual cycle, Kirtland’s Warbler uses early-successional habitats, often adjacent to or within active agricultural and forestry zones; see Habitat requirements. Consequently, the sources of pollution most likely to affect this species are agricultural and forestry runoff. The scope and severity of this threat are rated Unknown, given that no known pollutants have been confirmed near Kirtland’s Warbler breeding, migration or wintering habitat, and there are no reports of the negative effects of specific pollutants on the species’ survival.

Number of threat locations

In Canada, there are three threat-based locations for Kirtland’s Warbler as of 2023: (i) Garrison Petawawa in Renfrew County; (ii) Simcoe County, including the primary Simcoe County location and the Packard Tract and Museum Tract restoration sites; and (iii) the Parry Sound District, including Henvey Inlet, in the northeastern Georgian Bay area; see Severe Fragmentation. These sites were identified as geographically distinct areas, with singing males and/or confirmed nesting recorded in more than one year in the past 10 years, and are each independently vulnerable to the effects of wildfires and/or extreme weather events. There are most likely more than 10 wintering locations on various islands of The Bahamas and Turks and Caicos, given that some islands or groups of islands may be affected separately by weather events such as hurricanes.

Protection, status, and recovery activities

Legal protection and status

In Canada, Kirtland’s Warbler was assessed as Endangered by COSEWIC in 1979; this assessment was confirmed in 1999, 2000, 2008 and, most recently, 2024. It is listed as Endangered under Schedule 1 of Canada’s Species at Risk Act (Government of Canada 2019). The Kirtland’s Warbler is also protected by the Migratory Birds Convention Act, 1994 (Government of Canada 2017).

In Ontario, the species is listed as Endangered under Schedule 2 of the province’s Endangered Species Act (Government of Ontario 2020). In Quebec, it is not currently listed as Threatened or Vulnerable under the Loi sur les espèces menacées ou vulnérables (RLRQ, c E-12.01) (LEMV) (Act Respecting Threatened or Vulnerable Species; CQLR, c E-12.01), or on this Act’s Liste des espèces susceptibles d’être désignées menacées ou vulnérables (List of Plant and Wildlife Species Which Are Likely to Be Designated as Threatened or Vulnerable). The species is afforded protection under the Loi sur la conservation et la mise en valeur de la faune (RLRQ, c. C- 61.1) (LCMVF) (Act Respecting the Conservation and Development of Wildlife; CQLR, c. C-61.1). Under section 26 of the LCMVF, it is illegal to disturb, destroy or damage the eggs or nest of a mammal, bird, amphibian or reptile. It is also prohibited to capture, hunt and/or keep it in captivity.

In the U.S., Kirtland’s Warbler was listed as Endangered under the Endangered Species Act from 1973 to 2019. In 2019, the species was de-listed owing to sustained population increases since the 1990s and the achievement of the primary objectives in the recovery plan (USFWS 2019).

The species has no official conservation status in the nations where it overwinters. The Bahamas National Trust Act and National Parks Ordinance provide protection to wildlife species found in national parks in The Bahamas and the Turks and Caicos. However, the majority of suitable habitat for Kirtland’s Warbler on these islands is found outside the national parks, largely on community- or privately owned lands (USFWS 2019).

Non-legal status and ranks

The NatureServe global conservation status for Kirtland’s Warbler is G3 (Vulnerable). In Ontario, the Natural Heritage Information Centre (NHIC) ranks the species as S1B (Critically Imperilled Breeding). In Quebec, it is designated SNA (Not Applicable). At the U.S. state level, it is ranked S1 (Critically Imperilled) in Florida, Ohio, South Carolina and Wisconsin; S3 (Vulnerable) in Michigan; SNA in Indiana, Pennsylvania and Virginia; and SNR (Unranked) in Georgia (NatureServe 2022; Table 2). Since 2012, the species has appeared on the IUCN Red List as Near Threatened, as assessed by BirdLife International, indicating that it is close to meeting, but does not meet, the criteria for Vulnerable based on population size and trends, area of occupancy and threat of extinction (BirdLife International 2020).

^a At start of rank: G = Global; N = National; S = Subnational; B = Breeding. At end of rank: N = Non-breeding, M = Migrant. Numeric rank: 1 = Critically Imperilled; 2 = Imperilled; 3 = Vulnerable; 4 = Apparently Secure; 5 = Secure; NA = Not Applicable; NR = Not Ranked; ? = inexact numeric rank.

^b Listed as Endangered / Threatened / Special Concern (or equivalent designations) by the jurisdiction in question.

Land tenure and ownership

Along the Lake Erie shoreline of Ontario, the species has been observed during spring migration on a near-annual basis since the 1990s, at Point Pelee National Park (Birds Canada 2022b; Dobbie pers. comm. 2023); this area is identified as a migratory stopover site for the species (Cooper et al. 2017). A large portion of the consistently occupied breeding habitat is on active military land with restricted public access (Cybulski 2022; DND unpubl. data). The restoration sites at the Packard and Museum tracts are owned by Simcoe County, and the recently occupied areas in Parry Sound District are in French River Provincial Park and the Henvey Inlet First Nation (Burke pers. comm. 2023).

Recovery activities

In 2016, the Government of Canada’s Action Plan for the Kirtland’s Warbler was published, providing a preliminary assessment of the species’ critical habitat based on the information available up to 2011 (ECCC 2016). The action plan also highlighted the importance of creating suitable habitat for the species, in order to maintain and increase the size of the Canadian breeding population. Restoration of Red Pine–Oak habitat began in 2017 on two parcels of land, Packard Tract and Museum Tract, in Simcoe County, Ontario (Burke 2022; County of Simcoe 2024). The project’s primary goal is to create suitable Kirtland’s Warbler breeding habitat in an area where nesting has historically occurred (Speirs 1984), but also aims to provide habitat for other rare plant and wildlife species that occur in this ecosystem (Corace et al. 2010; Burke 2018). In 2022, singing male Kirtland’s Warblers were detected for the first time at the Packard Tract restoration site (Burke 2022; Burke pers. comm. 2022, 2023).

Information sources

References cited

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Collections examined

No collections were examined for the preparation of this report.

Authorities contacted

• Akresh, M. Director. Conservation Biology and Core Faculty, Antioch University New England. Keene, New Hampshire, USA
• Anctil, A. Biologiste, Coordonnateur CDPNQ – Faune. Centre de données sur le patrimoine naturel du Québec, Ministère de l’Environnement, de la Lutte contre les changements climatiques, de la Faune et des Parcs, Direction générale de la gestion de la faune et des habitats. Quebec City, Quebec
• Brett, J. Species at Risk Biologist. Canadian Wildlife Service, Environment and Climate Change Canada. Toronto, Ontario
• Burke, P. Senior Ecologist. GEI Consultants. Kitchener, Ontario
• Cooper, N. Research Ecologist. Smithsonian Migratory Bird Center. Washington, D.C., USA
• De Forest, L. Species Conservation Specialist. Conservation Programs Branch, Parks Canada. Halifax, Nova Scotia
• Dobbie, T. Park Ecologist – Nature Legacy. Parks Canada, Point Pelee National Park. Leamington, Ontario
• Ethier, D. Population Scientist. Birds Canada. Port Rowan, Ontario
• Ewert, D. Kirtland’s Warbler Program Director and Conservation Specialist. American Bird Conservancy. Lansing, Michigan, USA
• Filion, A. Scientific and GIS Project Officer. COSEWIC Science Support, Canadian Wildlife Service, Environment and Climate Change Canada. Gatineau, Quebec
• Gauthier, I. Biologiste, Coordonnatrice provinciale des espèces fauniques menacées et vulnérables. Ministère de l’Environnement, de la Lutte contre les changements climatiques, de la Faune et des Parcs, Direction générale de la gestion de la faune et des habitats. Quebec City, Quebec
• Jardine, C. Associate Director, Data Science and Technology. Birds Canada. Port Rowan, Ontario
• Jones, C. Provincial Zoologist – Invertebrates. Ontario Natural Heritage Information Centre, Ontario Ministry of Natural Resources and Forestry. Peterborough, Ontario
• Lopez, D. Conservation Biologist. Wisconsin Department of Natural Resources. Madison, Wisconsin, USA
• McDonald, R. Senior Environmental Advisor. Department of National Defence. Ottawa, Ontario
• Mensing, C. Fish and Wildlife Biologist. U.S. Fish and Wildlife Service. East Lansing, Michigan, USA
• Robert, M. Biologist, Migratory Birds Surveys. Canadian Wildlife Service, Environment and Climate Change Canada. Quebec City, Quebec
• Rupert, S. Promotion Officer. Parks Canada, Point Pelee National Park. Leamington, Ontario
• Saini, A. Scientific and GIS Project Officer. COSEWIC Secretariat, Canadian Wildlife Service, Environment and Climate Change Canada. Ottawa, Ontario
• Toews, D. Assistant Professor. Department of Biology, Pennsylvania State University. State College, Pennsylvania, USA
• Tuininga, K. Ecologist. Birks Natural Heritage Consultants, Inc. Barrie, Ontario
• Wu, J. Scientific Project Officer. COSEWIC Secretariat, Canadian Wildlife Service, Environment and Climate Change Canada. Ottawa, Ontario
• Wunderle, J. Wildlife Team Leader. International Institute of Tropical Forestry. U.S. Fish and Wildlife Service. Luquillo, Puerto Rico

Acknowledgements

Funding for the preparation of this report was provided by Environment and Climate Change Canada. First, the report writer would like to thank David Anthony Kirk and Jennie L. Pearce, the authors of the 2008 COSEWIC Assessment and Update Status Report on the Kirtland’s Warbler. Thanks also go to Louise Blight and Marcel Gahbauer, Co-chairs of the COSEWIC Birds Specialist Subcommittee, and Amit Saini, Scientific and GIS Project Officer and liaison with the COSEWIC Secretariat, for providing helpful guidance on the preparation of the draft report. Christian Artuso, Mike Burrell, Danielle Ethier and David Toews, members of the COSEWIC Birds Specialist Subcommittee, reviewed earlier versions of this status report. Special thanks are owed to the following authorities, who provided valuable data and/or advice: John Brett, Peter Burke and Ken Tuininga for insights and information on Kirtland’s Warbler conservation in Ontario; Michel Robert for updates on species sightings and ARU monitoring in Quebec; Chris Mensing and Davin Lopez for information on the Michigan and Wisconsin populations; and David Ewert, Joseph Wunderle and Nathan Cooper for the latest updates on the research on migration and wintering. Thanks also go to Alain Filion for providing NHIC data on Kirtland’s Warbler observations, and Catherine Jardine and Danielle Ethier at Birds Canada for providing access to the NatureCounts database. Karen Chung and Danielle Ethier assisted in map production and EOO and IAO calculations. Finally, much appreciation is owed to the citizen scientists and other volunteers who have contributed years of valuable data to the Michigan and Wisconsin Kirtland’s Warbler censuses, the Ontario Breeding Bird Atlas and eBird.

Biographical summary of report writer(s)

Alana Demko is a wildlife ecologist with over 15 years of research experience in academia, government and consulting. Her graduate research at Dalhousie University (M.Sc.) and the University of Windsor (Ph.D.) investigated the behavioural ecology of temperate and tropical warblers, in particular their vocal and territorial behaviour. Alana has conducted field research on several bird species at risk in Canada, the U.S. and the Caribbean, including two winters of Kirtland’s Warbler monitoring in The Bahamas and one season of nest searching and monitoring for the species in Michigan. In her current role as an Ecologist at LGL Limited, Alana’s work focuses on terrestrial wildlife habitat assessments and conservation and monitoring applications of bioacoustic technologies such as autonomous recording units (ARUs).

Appendix 1. Threats calculator for Kirtland’s Warbler

Species or Ecosystem Scientific name: Setophaga kirtlandii

Date: 2023-08-10

Assessor(s): Louise Blight, Peter Burke, Pete Davidson, Alana Demko, Richard Elliot, David Ewert, Kevin Hannah, Jennifer Heron, Andrew Horn, Colin Jones, Michel Robert, Ken Tuininga, Dean Whitehead

References: Ewert pers. comm. 2023; Fleming et al. 2016, 2019; Handler et al. 2014; Rockwell et al. 2012, 2017; Walkinshaw 1972; Wolcott et al. 2018. Also see Threats section in report for further citations.

Assigned overall threat impact: B-C = High-Medium

Impact adjustment reasons: None

Classification of Threats adopted from IUCN-CMP, Salafsky et al. (2008).