Greater Short-horned Lizard (Phrynosoma hernandesi): COSEWIC assessment and status report 2018

Official title: COSEWIC Assessment and Status Report on the Greater Short-horned Lizard (Phrynosoma hernandesi) in Canada 2018

Committee on the status of Endangered Wildlife in Canada (COSEWIC)
Special concern 2018

COSEWIC assessment summary

Assessment summary – November 2018

Common name: Greater Short-horned Lizard

Scientific name: Phrynosoma hernandesi

Status: Special concern

Reason for designation: In Canada, this species occurs in several scattered localities in grasslands of southern Alberta and Saskatchewan. New localities have been documented since the previous assessment, and the distribution of the species is no longer considered to be severely fragmented. Range-wide threats include habitat modification by invasive plants and increased vulnerability to summer droughts and freeze/thaw events associated with climate change. Approximately 70% of the population occurs in Grasslands National Park, but subpopulations outside the protected area, including all subpopulations in Alberta, are subject to additional threats including agriculture, oil and gas drilling, increased predation because of habitat modification, and other human developments. Current trends in population size and habitat quality in Alberta are unknown. The species is close to meeting criteria for Threatened because of its small range, inferred and projected reduction in habitat quality, its patchy distribution, and its specific habitat requirements.

Occurrence: Alberta, Saskatchewan

Status history: Designated special concern in April 1992. Status re-examined and designated Endangered in April 2007. Status re-examined and designated special concern in November 2018.

COSEWIC executive summary

Greater Short-horned Lizard
Phrynosoma hernandesi

Wildlife species description and significance

Greater Short-horned Lizard (Phrynosoma hernandesi) is the only species of lizard found in Alberta and Saskatchewan. The species occurs farther north than any other iguanid lizard species globally. It is the most widespread and generalist of all horned lizard species. Greater Short-horned Lizard is a small (snout-vent length of approximately 69 mm for adult females), dorso-ventrally flattened lizard with a fringe of protruding scales along the sides, and an array of ‘horns’ and a deep hornless notch across the back of the head. The blotched dorsal colouration and ability to remain motionless provide the lizards an excellent camouflage, helping protect them from predators and allowing them to ambush prey.

Distribution

Greater Short-horned Lizard is distributed throughout the North American west, from central Mexico to southern Alberta and Saskatchewan. The lizards occur in distinct habitat areas, four in Alberta and two in Saskatchewan. In Alberta, the species occurs in scattered habitats along the South Saskatchewan River, within the Manyberries Hills, along the Chin Coulee/Forty Mile Coulee complex, and along the Milk River and its associated tributaries. In Saskatchewan, Greater Short-horned Lizard primarily occurs within the East and West Blocks of Grasslands National Park.

Habitat

In Canada, Greater Short-horned Lizard generally occupies sparsely vegetated, south-facing slopes with friable (crumbly) soils and patchy vegetation cover. This pattern provides shade from the sun, as well as overnight shelter. Dense vegetation may inhibit movements. The species occurs throughout the slopes, from the valley and gulley bottoms, mid-slope, and into adjacent upland grasslands.

Biology

Greater Short-horned Lizard is a generalist insectivore, consuming ants as well as crickets, beetles, spiders, and other arthropods. In Canada, females give birth to live young annually in late July or early August. Clutch sizes vary widely but may exceed 10 offspring. Females tend to establish a series of small territories within a larger home range during the summer active period and move relatively short distances. Activity has been recorded between April and November. Greater Short-horned Lizard overwinters approximately 10 cm below the soil surface.

Population size and trends

Since the initial agricultural development in the early 20th century, declines in habitat connectivity, quality, and quantity have occurred. There are no clear trends in subpopulations that have been monitored since the 1980s. It is likely that subpopulations in at least some localities have been extirpated during the past two decades (for example, localities near Medicine Hat). Continuing occupancy has not been recently confirmed at all localities, particularly along the South Saskatchewan River and Milk River. New localities near Manyberries Hills have been recorded, which suggests that not all occupied habitat has been documented. The population size is poorly known but probably exceeds 10,000 adults.

Threats and limiting factors

The long-term viability of the Greater Short-horned Lizard population in Canada is threatened by a variety of anthropogenic activities. Threats include habitat modification by invasive plants, droughts and fluctuations in snow cover associated with climate change, increased predation due to habitat modification, land conversion into agriculture, oil and gas drilling, and recreational activities. The species’ distribution in Canada is likely limited by a combination of historical habitat conversion and physiological and behavioural restrictions, acting in conjunction with climatic barriers.

Protection, status, and ranks

In Canada, Greater Short-horned Lizard is listed as Endangered on Schedule 1 under the Species at Risk Act. In Alberta, the species is listed as Endangered in Schedule 6 of the provincial Wildlife Act. In Saskatchewan, the provincialWildlife Act prohibits unauthorized killing, disturbance, collection, harvest, capture, sale, and export of wildlife without a permit. The species is not protected in the United States or internationally. In Alberta and Saskatchewan, Greater Short-horned Lizard has been assigned the sub-national rank of S2, indicating that the species is considered imperilled or at high risk of extinction. A global rank of G5 indicates that on a range-wide scale, Greater Short-horned Lizard is considered secure, or common, widespread, and abundant.

Technical summary

Scientific name: Phrynosoma hernandesi

English name: Greater Short-horned Lizard

French name: Lézard à petites cornes majeur

Range: Alberta, Saskatchewan

Demographic information

Generation time (usually average age of parents in the population; indicate if another method of estimating generation time indicated in the IUCN guidelines(2011) is being used):

3 to 4 years (see Life Cycle and Reproduction)

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

Yes, observed and inferred decline, based on the presumed extirpation from some localities in the Medicine Hat area and ongoing threats

Estimated percent of continuing decline in total number of mature individuals within [5 years or 2 generations]:

Unknown

[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over the last [10 years, or 3 generations]:

Unknown

[Projected or suspected] percent [reduction or increase] in total number of mature individuals over the next [10 years, or 3 generations]:

Overall threat impact of “medium” based on threats calculator results indicates a suspected decline of 3 to 30% over the next 3 generation period from threats acting over the next 10 years.

[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over any [10 years, or 3 generations] period, over a time period including both the past and the future:

Unknown

Are the causes of the decline a) clearly reversible and b) understood and c) ceased?

a. No
b. Yes
c. No

Are there extreme fluctuations in number of mature individuals?

Unknown but possible. Large multi-annual fluctuations have been recorded within the Canadian range of the species (see Fluctuations and Trends), but whether the fluctuations are extreme (that is, an order of magnitude) and occur synchronously over large areas is uncertain.

Extent and occupancy information

Estimated extent of occurrence (EOO):

28,463 km²

Index of area of occupancy (IAO) (Always report 2x2 grid value):

480 km²

Is the population “severely fragmented”:

a. No
b. Yes

Number of “locations”^* (use plausible range to reflect uncertainty if appropriate):

Most plausible number is >10 based on the threat of invasive plants modifying habitat using land ownership as a proxy for different management regimes; could be as low as six, corresponding to each subpopulation and based on climate change and severe weather, but there is much uncertainty.

Is there an [observed, inferred, or projected] decline in extent of occurrence?

No

Is there an [observed, inferred, or projected] decline in index of area of occupancy?

No

Is there an [observed, inferred, or projected] decline in number of subpopulations?

No, if each habitat area is considered a subpopulation.

Is there an [observed, inferred, or projected] decline in number of “locations”*?

Yes, observed decline as some locations near Medicine Hat appear to have been extirpated

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

Yes, inferred and projected decline in habitat quality (see Threats)

Are there extreme fluctuations in number of subpopulations?

No

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

¹ See Definitions and Abbreviations on COSEWIC website and International Union for Conservation of Nature (IUCN) (Feb 2014) for more information on this term.

Number of mature individuals (in each subpopulation)

Quantitative analysis

Probability of extinction in the wild is at least [20% within 20 years or 5 generations, or 10% within 100 years]: Not done due to lack of data

Threats (actual or imminent, to populations or habitats, from highest impact to least)

Was a threats calculator completed for this species?
Yes, on 18 April 2017

1. Other ecosystem modifications: Invasive plants (threat impact Medium)
2. Climate change & severe weather: Habitat shifting & alteration (Medium – Low) and Other impacts (Medium – Low)
3. Energy production & mining: Oil & gas drilling (threat impact Low)
4. Agriculture: Annual & perennial non-timber crops (threat impact Low)
5. Human disturbance: Recreational activities (threat impact Low)
6. Invasive & other problematic species: Problematic native species (threat impact Low)

What additional limiting factors are relevant?

• Susceptibility to sporadic extreme weather events causing high local mortality
• Physiological limitations at northern range limit contributing to high mortality

Rescue effect (immigration from outside Canada)

Status of outside population(s)?

Vulnerable (S3) in Montana (the only U.S. state bordering the Canadian range)

The range of this species extends across the United States, where subpopulations have also declined. The source-sink dynamics of this species are unknown, yet this species has the potential to disperse long distances:

Not applicable

Is immigration known or possible?

Not known but possible for some subpopulations in the Milk River and Grasslands National Park habitat areas; see Rescue Effect

Would immigrants be adapted to survive in Canada?

Probably

Is there sufficient habitat for immigrants in Canada?

Yes

Are conditions deteriorating in Canada?⁺

Possibly, due to some threats, in localized areas (see threats)

Are conditions for the source population deteriorating?⁺

Unknown

Is the Canadian population considered to be a sink?⁺

No

Is rescue from outside populations likely?

Possible for some subpopulations near the international border but expected to be slow and of minor significance due to low dispersal capabilities of the lizards. Many subpopulations in Canada are in habitat geographically isolated from occupied habitat in Montana; see Rescue Effect

⁺ See Table 3 (Guidelines for modifying status assessment based on rescue effect).

Data-sensitive species

Is this a data sensitive species? No

Status history

COSEWIC: Designated special concern in November 2017.

Status and reasons for designation:

Status: Special concern

Alpha-numeric codes: Not applicable

Reasons for designation: In Canada, this species occurs in several scattered localities in grasslands of southern Alberta and Saskatchewan. New localities have been documented since the previous assessment, and the distribution of the species is no longer considered to be severely fragmented. Range-wide threats include habitat modification by invasive plants and increased vulnerability to summer droughts and freeze/thaw events associated with climate change. Approximately 70% of the population occurs in Grasslands National Park, but subpopulations outside the protected area, including all subpopulations in Alberta, are subject to additional threats including agriculture, oil and gas drilling, increased predation because of habitat modification, and other human developments. Current trends in population size and habitat quality in Alberta are unknown. The species is close to meeting criteria for Threatened because of its small range, inferred and projected reduction in habitat quality, its patchy distribution, and its specific habitat requirements.

Applicability of criteria

Criterion A: Criterion is not met, because there is no robust information on the magnitude of population decline over the past 3 generation period or projected into the future, but the threats calculator indicates a 3 to 30% suspected decline.

Criterion B: Criterion is not met. Although IAO is below the threshold value for Endangered, only one of the subcriteria are met (B2b(iii) – decline in habitat quality). Because of the highly patchy distribution and specific habitat requirements of the lizards, the population may become severely fragmented in future, but insufficient information exists at present on the viability of subpopulations in habitat patches at the landscape scale.

Criterion C: Criterion is not met. Population size most likely exceeds 10,000 mature individuals.

Criterion D: Criterion is not met. The population is not very small or restricted.

Criterion E: Not applicable. PVA was not done due to lack of data.

Preface

Since the preparation of the previous COSEWIC status report for Greater Short-horned Lizard in 2007, new research has been conducted in both Alberta and Saskatchewan. Genetic analyses using two mitochondrial and one nuclear gene found that the species colonized Alberta following the retreat of the Laurentide ice sheet from a single source population approximately 10,000 years ago (Leung 2012; Leung et al. 2014). The analyses also revealed that geographically isolated Greater Short-horned Lizard subpopulations in Alberta and Saskatchewan are not genetically distinct in terms of the genes sequenced. This indicates that they were historically interconnected, but no inferences can be made on more recent connectivity patterns (Leung 2012; Leung et al. 2014).

New surveys conducted as part of a predictive habitat modelling study in Grasslands National Park expand the occupied area in Saskatchewan (Fink 2014; Welsh et al. 2015; S. Licciolo personal communication 2018). These surveys indicate that the subpopulation in the West Block of the park is likely larger than was suggested following the previous surveys conducted in 1994 and 1995 (Powell et al. 1998). Ongoing surveys by Alberta Environment and Parks (AEP), MULTISAR, the Royal Saskatchewan Museum (RSM), Parks Canada, and others continue to contribute new observations throughout the Alberta and Saskatchewan range. These surveys have identified new occupied habitat, indicating that there may still be unidentified patches of suitable habitat (S. Pruss personal communication 2014; Welsh et al. 2015; S. Robertson personal communication 2016; S Licciolo personal communication 2018).

No Aboriginal traditional knowledge was available for the species (N. Jones personal communication 2016).

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 COSEWI C 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 (2018)

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)
(Note: Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.)

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)
(Note: Formerly described as “Not In Any Category”, or “No Designation Required.”)

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

Data deficient (DD)
(Note: 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.)

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.

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

Greater Short-horned Lizard (Phrynosoma hernandesi Girard, 1858) is placed in the family Phrynosomatidae, all members of which are endemic to western North America. The classification is as follows:

Class Reptilia
Order Squamata
Suborder: Iguania
Family: Phrynosomatidae
Genus: Phrysonoma
Species: Phrynosoma hernandesi

The species in Alberta and Saskatchewan, formerly known as Eastern Short-horned Lizard (Phrynosoma douglasii brevirostre; Russell and Bauer 1993), was reclassified in accordance with new information by Zamudio et al. (1997). Previously, all short-horned lizards were classified as part of Phrynosoma douglasii, with six subspecies primarily based upon morphological considerations (Reeve 1952). Two of these former subspecies had distributions that ranged into Canada: Phrynosoma douglasii douglasii, Pygmy Short-horned Lizard, in south-central British Columbia, and Phrynosoma douglasii brevirostre, Eastern Short-horned Lizard, in Alberta and Saskatchewan.

Zamudio et al. (1997) provided genetic and morphological evidence to support division of Phrynosoma douglasii (sensu lato) into two separate species. Those populations located to the west and previously designated as the subspecies P. d. douglasii, were designated Phrynosoma douglasii (sensu stricto). The rest of the subspecies within Phrynosoma douglasii, that is, those in the Great Plains, Colorado Plateau, and high-altitude localities along the Rocky Mountains in the southern United States and Mexico, were designated P. hernandesi (Hammerson and Smith 1991; Zamudio et al. 1997; Smith et al.1999). While there is debate regarding potential paraphyly within the P. hernandesi group (Zamudio et al. 1997; Sherbrooke 2003), Crother et al. (2012) does not recognize any subspecies.

Crother (2012) determined that Greater Short-horned Lizard is the most credible common name for the species. The common name in French is Lézard à petites cornes majeur.

Morphological description

Horned lizards are small, well-camouflaged lizards with a rim of protective spikes around the posterior margin of the skull. The relative length and position of these horns, varies with each of the 17 currently recognized species within Phrynosoma (Leaché and McGuire 2006). All horned lizards are dorso-ventrally flattened, with a fringe of protruding scales along the sides. They have broad heads, wide bodies, and short tails, giving them a squat, stocky appearance. Their somewhat waddling gait in combination with their stature likely led to the slang terms of “Horny toad” or “Horned toad” often used in popular texts.

Greater Short-horned Lizard is characterized by relatively short, though still noticeable, parietal and squamosal horns (Sherbrooke 2003; Stebbins 2003; Figure 1). They have a single row of fringe scales along each side (Russell and Bauer 2000; Sherbrooke 2003; Stebbins 2003). Colouration varies by region but is always highly cryptic, blending in with local substrates. The back has a grey, beige, tan or even reddish base speckled with white and covered with blotches of darker brown and with a pair of darkest blotches behind the head (Russell and Bauer 2000; Stebbins 2003). The ventral surface is light coloured (beige or lighter), and sometimes tinged with yellow or orange (Russell and Bauer 2000; Stebbins 2003).

In field studies in Alberta (Powell and Russell 1985a), the average snout-vent length (SVL) was 69 mm for adult females and 52 mm for adult males. Males of all ages exhibit enlarged post-anal scales (Powell and Russell 1985a) and a noticeable swelling at the base of the tail during the breeding season (Stebbins 2003). Greater Short-horned Lizard exhibits marked sexual dimorphism, with females growing considerably larger than males (Powell and Russell 1984, 1985a). Both sexes grow at the same rate, but males cease growth and reach reproductive maturity earlier than females by at least one year (Powell and Russell 1985a). An adult female may attain an average non-gravid mass of 18 g, whereas an adult male will average 10 g (Powell and Russell 1985a).

Population spatial structure and variability

Greater Short-horned Lizard occurs in widely separated drainages and coulee systems throughout southeastern Alberta and southwestern Saskatchewan. As well as being separated by distance, the major occupied drainages are isolated by unsuitable habitat, further reducing the probability of dispersal. Each occupied drainage is considered a disjunct habitat area with connectivity of habitat within the drainage (see Canadian Range).

While dispersal behaviour of this species is incompletely understood (Environment Canada 2015), mark-recapture studies indicate that the lizards are relatively sedentary (see Dispersal and Movements); dispersal between patches of habitat separated by as little as 10 km would require multiple generations and successful overwintering and breeding in the hostile matrix between habitat patches. The Alberta habitat areas are separated by 13 to 50 km (FWMIS 2016; Figure 2). Due to dispersal limitations, lizards within each disjunct habitat area are considered a separate subpopulation.

Additional sub-structuring may occur within the above subpopulations. Occurrence records within a habitat area may be separated by large distances, despite intervening suitable habitat (Harvey et al. 2015; Figure 2). For example, in the South Saskatchewan River habitat area, one record from 2001 is 19 km from the nearest more recent record (since 1995), but continuous suitable habitat exists between the two sites. Some recent records (2000 to 2016) are separated by as much as 70 km despite apparent connecting habitat and intervening historical records (Figure 2). It is possible that occupied habitat between records exists, but it has not been identified.

Despite the apparent geographic isolation, genetic analysis using one nuclear (RAG-1) and two mitochondrial DNA (ND1/ND2) genes sequenced from 95 lizard tail tips identified little genetic structuring across localities in Saskatchewan and Alberta (Leung 2012; Leung et al. 2014). Rather, consistent clustering of mitochondrial and nuclear DNA sequences from across Canada suggests that lizards from all sampled localities originated from a single glacial refugium. This suggests that either there has been insufficient time for genetic differentiation since isolation, or the population clusters remain in genetic contact (Leung et al. 2014). Despite lack of evidence for genetic structure within the population, observers have noted differences in colouration of individuals in isolated localities, which may be reflective of local adaptation (Powell 1982).

Further study is currently underway using microsatellite markers that is revealing more recent (within 100s of years) connectivity patterns of Canadian Greater Short-horned Lizard subpopulations (Sim et al. 2014). Preliminary analysis of microsatellite data indicates that there is genetic structuring. Structure analysis indicates that there are three higher-level groups within the Canadian population. One group includes individuals in Montana and most of Alberta (includes individuals sampled from near Bow Island, Manyberries and Nemiskam). A second group includes individuals in the East and West Blocks of Grasslands National Park. A third group includes individuals in the Chin Coulee and Milk River area. There is significant cross-assignment, indicating that some past migration has occurred between all clusters. All Canadian clusters are more similar to each other and dissimilar from individuals sampled in Colorado (T. Fulton personal communication 2018).

Designatable units

A single designatable unit is proposed for Greater Short-horned Lizard in Canada as this species does not meet the COSEWIC (2015) criteria based on ‘subspecies or varieties’ or ‘discrete and evolutionary significant populations’.

In terms of discreteness, there is limited evidence of genetic distinctiveness among geographically distant habitat areas (Leung et al. 2014). While recent preliminary analysis indicates some genetic clustering, there are high amounts of cross-assignment among groups (T. Fulton personal communication 2018). Therefore, these groups are not considered discrete.

All occurrences are within a single reptile and amphibian faunal province (“Prairie” in 2016 map in COSEWIC 2017). No morphological or behavioural differences among lizards from the different habitat areas have been documented, although some colour differences have been noted in lizards from isolated localities.

Special significance

Greater Short-horned Lizard is the only lizard species found in Alberta and Saskatchewan. The species occurs farther north than any other member of Phrynosoma or any iguanid lizard species globally (Russell and Bauer 1993). Where they do occur in Canada, they are found in scattered, isolated subpopulations, comprising the northernmost extension of the overall distribution for the species.

Distribution

Global range

Of the 17 species of the genus Phrynosoma, Greater Short-horned Lizard is the most widely distributed in terms of altitude, latitude, and overall range. The species occurs from central Mexico, through the Great Plains of United States, to the southernmost portions of the Canadian prairies (Russell and Bauer 1993, 2000; Sherbrooke 2003; Stebbins 2003; Figure 3).

Canadian range

The proportion of the global distribution for Greater Short-horned Lizard within Canada is less than 5% (ASRD 2004). Greater Short-horned Lizard occurs in a limited number of widely scattered habitat areas across the southeastern corner of Alberta and in extreme southwestern Saskatchewan (Powell and Russell 1991a, 1992a, 1998; Powell et al. 1998; James 2002, 2003; ASRD 2004; Figure 4). Its most northern records are from along the eastern banks of the South Saskatchewan River, north of Medicine Hat in Alberta, at approximately 50⁰10’N (Powell and Russell 1998; FWMIS 2016). Milner (1979) listed the southeastern portions of the Red Deer River as part of the range of this species in Alberta, but Laird and Leech (1980) disregarded this suggestion, as there are no confirmed records from this far north. The most western record is near the village of Grassy Lake, Alberta, based on a single observation from 1923 (FWMIS 2016). The most eastern record is to the west of the West Poplar River, within the East Block of Grasslands National Park in Saskatchewan (Powell and Russell 1998).

In Alberta, occupied habitat is spread within four widely distributed habitat areas: 1) South Saskatchewan River; 2) Manyberries Hills; 3) Chin Coulee/Forty Mile Coulee complex; and 4) Milk River and its associated tributaries (James 2002; ASRD 2004; Figure 2). These four habitat areas are isolated from each other by distances of 10 to 35 km (Powell and Russell 1992a; James 2002; ASRD 2004; Figure 2). A fifth habitat area near Grassy Lake, Alberta, is no longer considered occupied (see Habitat trends).

In Saskatchewan, Greater Short-horned Lizard occurs primarily within the East and West Blocks of Grasslands National Park (GNP) and is isolated from habitat areas in Alberta and from each other by distance and natural topographic features (Powell and Russell 1992b, 1998; Powell et al. 1998; Figure 4). A few observations have been made outside the park, within 1 km of the park boundary. Habitat in Saskatchewan is associated with the Milk River (Missouri drainage) system (Powell and Russell 1992b, 1998; Powell et al. 1998), and shares similar habitat characteristics as the Alberta portion of the habitat area along the Milk River. In Saskatchewan, all records of Greater Short-horned Lizard are from south of 49 degrees 30’N, within 30 km of the Canada/U.S. border (Powell and Russell 1998; Powell et al.1998). Distribution in Saskatchewan is confined to Grasslands National Park and its immediate vicinity.

Extent of occurrence and area of occupancy

The extent of occurrence (EOO) and the index of area of occupancy (IAO) were calculated using available records from Alberta and Saskatchewan (1995 to 2017). Data sources include records used to identify Critical Habitat for Greater Short-horned Lizards in the federal recovery strategy (Environment Canada 2015), the Alberta Fish and Wildlife Management Information System database (FWMIS 2016), the Saskatchewan Conservation Data Centre database (SCDC 2016), and recent surveys in Grasslands National Park (S. Licciolo personal communication 2018). Observations from before 1995 were considered historical and were not included in the analysis. The 1995 threshold allows the inclusion of the most recent surveys throughout all known occupied habitats in Alberta and Saskatchewan.

The EOO is estimated to be 28,463 km², based on a minimum convex polygon containing all known occurrences from 1995 to 2017 inclusive (Appendix 1). The IAO was calculated based on the number of occupied 2 km x 2 km grid cells as 480 km² (Appendix 1).

The EOO given here is significantly larger than in the previous status report (8,830 km² in COSEWIC 2007). Previous EOO estimates separated Alberta and Saskatchewan records and devised two minimum convex polygons. The primary reason for the difference between the 2007 and current EOO estimates is the vast unoccupied area between the easternmost Alberta subpopulation and the westernmost Saskatchewan subpopulation, which is included in the current calculation. When the 2007 EOO is recalculated as a single polygon using observations from 1991 to 2006, inclusive, the same range of years as used in the previous status report, the EOO is estimated to be 26,532 km², slightly less than the 28,463 km² estimated here (Appendix 2). Recent records from the East Block of Grasslands National Park and the Milk River habitat area contributed to the increase in EOO.

The previous status report estimated the IAO to be 220 km², considerably smaller than the current estimate of 480 km². Recent surveys in West Block of Grasslands National Park contributed numerous new records (Fink 2014; Welsh et al. 2015), resulting in an increase in the known IAO. In Alberta, new records in the Manyberries Hills also contributed to the increase.

Search effort

Distribution records for Greater Short-horned Lizard were compiled from the following sources: historical observations (summarized in Powell and Russell 1998), targeted surveys (Powell 1982; Powell and Russell 1992a; James 1997, 2002, 2003; Powell et al. 1998; Leung 2012; Fink 2014; Welsh et al. 2015; S. Liccioli personal communication 2018), and incidental observations reported to provincial databases and to Parks Canada (Table 1).

^aIt is assumed that searchers with GPS tracklogs walked at speeds of 2.1 km/h (ASRD 2004). Kilometres searched divided by 2.1 km/h yields hours searched, allowing direct comparison among the surveys.

Greater Short-horned Lizard is difficult to survey, due to its low densities, cryptic colouration, and tendency to remain motionless even when approached closely. As the lizards have limited mobility and leave few indications of their presence, such as tracks, trapping them or using some other index of presence is not viable. Greater Short-horned Lizard in Alberta and Saskatchewan has been surveyed on foot using visual encounter methods (for example, Powell 1982; Powell and Russell 1996; Powell et al. 1998; James 2002, 2003; Fink 2014; Welsh et al. 2015). Surveys typically take place in late July and early August, as this coincides with parturition. More captures per unit effort are expected at this time than earlier in the season because of the increased total number of individuals and because neonates seem more easily flushed than mature individuals (James 2002). Post-parturition behavioural changes in female lizards may also contribute to higher capture rates. Juveniles are useful for indicating occupancy at a given site but yield little information in regards to population size of mature individuals.

Alberta

In Alberta, search effort has concentrated in historically occupied areas as initially determined by Powell and Russell (1992a). A subsequent survey was conducted in the summer of 2001 and 2002 (James 2002, 2003; ASRD 2004). While the survey in 2001 yielded numerous records, the 2002 Alberta survey effort was largely unsuccessful, due to poor search conditions throughout the survey period (James 2003). The objective of the 2001 and 2002 surveys was to search all historically occupied habitat in Alberta, which was documented at the level of the Quarter-Section-Township-Range format (Powell et al. 1998; James 2002, 2003). Searches carried out in 1991 in Alberta verified the presence of lizards at 16 of the 28 (57%) sections (each section is one square mile) where they had been previously recorded (Powell and Russell 1992a). In the 2001 and 2002 surveys, 59 sections were searched (48 of which had previous records; 81%). Lizards were recorded on 19 sections (32%), three of which had no preceding records (5%). Of searches of sections with preceding records, 33% were confirmed occupied in 2001 or 2002 (James 2003; ASRD 2004).

Since the surveys in 2001 and 2002, searches by the oil and gas industry, MULTISAR land inventories, University of Calgary researchers, and those associated with provincial monitoring of Greater Short-horned Lizard have covered small portions of the species’ range (FWMIS 2016). These surveys resulted in the finding of lizards in all four disjunct habitat areas in Alberta (FWMIS 2016; S. Robertson personal communication 2016). While not all historical localities have been recently surveyed, coverage has been sufficient to infer continuing occupancy at most historically occupied areas (Figure 2).

Additional search effort in Alberta is needed along the South Saskatchewan River and Milk River drainages. Both drainages have extensive areas of apparently suitable habitat and historical observations of Greater Short-horned Lizards, but no recent confirmed occupancy. Effort in these areas is ongoing, and some areas have been surveyed and no lizards observed (S. Robertson personal communication 2016). There have been no observations from the Medicine Hat/Redcliff area since 2000, and only four observations have been recorded since 1988 (FWMIS 2016). Targeted surveys conducted in the Medicine Hat/Redcliff area in 2017 failed to detect Greater Short-horned Lizard (S. Robertson personal communication 2018).

Saskatchewan

In Saskatchewan, search effort has concentrated throughout the Frenchman River Valley and the associated Bearpaw shale badlands in the West Block of Grasslands National Park (Powell et al. 1998; Fink 2014; Welsh et al. 2015). Initial surveys of the West Block were conducted in 1995 and 1996 (Powell et al. 1998). In these surveys, approximately 200 person-hours were expended in 1995 and approximately 50 person-hours in 1996. More recent surveys were conducted in 2009 to 2018 (Fink 2014; Welsh et al.2015; N. Cairns personal communication 2018; S. Liccioli pers comm. 2018). An occupancy-sampling scheme was attempted in the West Block of Grasslands National Park in 2009 but was unsuccessful at documenting lizards within the predetermined search plots (K. Ellingson unpubl. data). Rather, the survey yielded 67 incidental records outside these plots. A second survey of the West Block in 2010 covered approximately 650 km of transect (2 m-wide transect; 130 ha) and yielded 131 records. Additional surveys in the West Block of Grasslands National Park were conducted in 2017 and in 2018. The sites where lizards where found in 2017 are incorporated in this report, but the details of the search effort and numbers of lizards found are not available at this time (S. Liccioli personal communication 2018). Newly acquired lands in the West Block of Grasslands National Park not surveyed in 2009 and 2010 were surveyed in 2015 (Welsh et al. 2015). In 2018, the same areas of the older portion of the West Block (384 km) and the newly acquired lands (120 km) as surveyed in 2015 were resurveyed using the same methods (N. Cairns personal communication 2018). The 2018 West Block surveys yielded 86 and 19 records, respectively.

In addition to surveys in the Grasslands National Park, a survey was conducted in the Val Marie Community Pasture northwest of the West Block of Grasslands National Park in 2010. This area was searched due to habitat similarities and close proximity to occupied habitat. Approximately 220 km of transect were searched (46 ha), but the species was not detected (K. Ellingson unpubl. data 2010). Additional suitable habitat may exist within the Mankota Community Pasture, but has not been surveyed.

In the East Block of the Grasslands National Park, surveys were conducted along the coulees associated with Rock Creek and Butte Creek in 1995 and 1996 (Powell et al. 1998). Welsh et al. (2015) conducted a significant search in the East Block of Grasslands National Park (approximately 300 km of transect, or 60 ha), but the area searched did not correspond to where Powell et al. (1998) surveyed in 1995 and 1996. Observations in 2013 by the Royal Saskatchewan Museum BioBlitz (Heisler et al.2014) and by K. Welsh in 2015 (Welsh et al. 2015) have clustered in a small area north of the observations originally made in 1995 and 1996 by Powell et al. (1998) (Figure 5). Additional search effort is needed to evaluate continuing occupancy in the East Block of Grasslands National Park where Powell et al. (1998) observed lizards, but no observations have been reported since that time. Unfortunately, null observations are not generally recorded in any observation databases in Alberta or Saskatchewan.

Habitat

Habitat requirements

Greater Short-horned Lizard inhabits an array of habitat types over a broad longitudinal range: short-grass prairie on the Great Plains, sagebrush communities in the Great Basin, and high elevation mountain hillsides (up to 3170 m) and valleys in the south of their distribution (Sherbrooke 2003). In Canada, the occupied area is part of the northern extremes of the Great Plains within the Northern Mixed Prairie region (Coupland 1992). In Alberta, this area is classified as the Dry Mixed-grass subregion (NRC 2006), whereas in Saskatchewan it is part of the Mixed Grassland ecoregion (Acton et al. 1998).

In Alberta, a community comprised of a blend of the mid-height grass Needle-and-Thread Grass (Hesperostipa comata) and the short-grass Blue Grama(Bouteloua gracilis) makes up the majority of the vegetation (NRC 2006). In the Manyberries Hills, a mixture of the mid-height Western Wheatgrass (Pascopyrum smithii) grows in combination with Blue Grama (NRC 2006). In Saskatchewan, the primary vegetation community in the occupied areas is Blue Grama-Needle-and-Thread Grass assemblage (Coupland 1950).

Habitat is usually composed of rugged terrain, including coulees, canyons, badland areas, partially stabilized shale dunes, and slopes associated with tributaries to watercourses (Powell and Russell 1998). Habitat characteristics vary among the six disjunct habitat areas in Alberta and Saskatchewan, but eroded slopes are a common feature. The eroded inclines and disturbed vegetation patterns associated with these landscapes provide a mix of exposed substrate interspersed with vegetation. Slopes also offer good drainage and loose soils for shelter and overwintering habitat (Mathies and Martin 2008). The lizards occur throughout the slope, including valley bottoms and adjacent upland grasslands. Greater Short-horned Lizard often burrows into loose, friable soil in eroded habitats on cool nights during the active season and for hibernation. Burrowing behaviour has been well documented for horned lizards (Heath 1965; Mathies and Martin 2008) and has been observed in the Canadian population (Laird and Leech 1980; James 1997).

The presence of vegetation interspersed with patches of exposed substrate is consistently present in occupied habitats, providing shade from the sun as well as overnight shelter (James 1997; Fink 2014). In Alberta, James (2002) found that the occupied microhabitats were on the average composed of 52% bare soil (n = 125; range 0% - 85%). In Saskatchewan, Fink (2014) found that Greater Short-horned Lizard selected microsites with a high diversity of vegetation cover types and a high amount (25 to 50%) of bare soil, consistent with observations in Alberta. Dense vegetation is likely a deterrent to Greater Short-horned Lizard, as it impedes movements (Newbold 2005; Rieder et al. 2010) and may prevent burrowing into the soil.

Overwintering habitat is within or near occupied summer habitat. Hibernation sites have been found on sheltered south-facing slopes in southeast Alberta (Powell and Russell 1994), although studies in other parts of the species’ range have not found aspect to be important (Mathies and Martin 2008). Hibernation sites can be low on the slope (Powell and Russell 1994) and may be steep relative to other available sites (Mathies and Martin 2008). Hibernation sites may be positioned on the slope such that they accumulate snow in winter (Powell and Russell 1993, 1994). In some instances, hibernation sites were in close proximity to burrows created by other small animals, but it is unclear if lizards used the burrow to access a below-ground overwintering site.

Habitat trends

Alberta

Grazing is the predominant land use (55%) in the Dry Mixed-grass subregion of Alberta (NRC 2006). In addition to grazing, approximately 35% is under dry-land cultivation, and 10% is irrigated (NRC 2006). Most occupied habitat in Alberta is generally ill suited for cultivation due to its steep and uneven topography and unproductive soils. There is no evidence that light grazing significantly damages habitat for Greater Short-horned Lizard (Newbold and MacMahon 2008), although heavy use may decrease habitat quality and lizard densities (Jones 1981). While the current grazing practices appear to be a compatible land use in Greater Short-horned Lizard habitat, habitat loss and degradation have occurred and may be ongoing in some areas.

The large-scale habitat conversion from grassland to cultivation in the early 20th century likely contributed to a reduction in the overall distribution of the species and habitat connectivity in Alberta, where approximately 45% of the Dry Mixed-grass subregion was altered for cultivation (NRC 2006). Cultivation continues in present times, but the rate of grassland conversion is unknown. A 1923 record of Greater Short-horned Lizard from near the village of Grassy Lake is in an area where the remaining suitable habitat for the species is currently extremely limited. It is the most western of all records for the species in Alberta (Powell and Russell 1991a). This record suggests that distribution of Greater Short-horned Lizard once extended the full length of Forty Mile Coulee, perhaps even connecting, at one time, with the South Saskatchewan River populations. This implies that there may have been an upper Forty Mile Coulee population that has become extirpated since 1923, probably related to the cultivation, damming, and irrigation along the watercourse.

More recent habitat loss has occurred along Forty Mile Coulee, where the construction of an irrigation reservoir, completed in 1989, in combination with the widespread cultivation and irrigation that surround the coulee, has likely reduced available habitat (Chin et al. 1990; Powell and Russell 1992b; James 2002) (Appendix 3). The irrigation reservoir is approximately 11 km long. In surveys conducted shortly after the reservoir was completed, the habitat was considered destroyed and was thought to no longer support a Greater Short-horned Lizard population (James 2002). Recent surveys have determined that Greater Short-horned Lizard continues to occupy habitat south of the primary dam, although the amount of habitat is likely reduced (James 2002; FWMIS 2016). The expansion of irrigation along the South Saskatchewan River is also noticeable and likely results in some habitat loss.

Habitat loss has occurred where petrochemical developments, with associated roads, pipelines, and well-site development, have been extensive (Alberta Energy Regulator (AER) 2016; Figure 6). While new well development has decreased in recent years in the vicinity of the Milk River and Chin Coulee/Forty Mile Coulee habitat areas, new well development continues, albeit at a slower pace, near occupied habitat along the South Saskatchewan River and within the Manyberries Hills (Appendix 3). Most of the habitat reclamation has occurred in the Milk River and tributaries habitat area (30.4%), but little reclamation has occurred in the South Saskatchewan River habitat area (6.7%). It is unknown if reclaimed areas provide suitable habitat for Greater Short-horned Lizards.

Saskatchewan

In Saskatchewan, the known occupied habitat is almost entirely within the existing and proposed borders of Grasslands National Park (SCDC 2016; Figure 5). In the West Block, a portion of the available habitat is grazed by bison, and the remainder is grazed by cattle. Occupied habitat in the East Block is primarily privately owned and leased land within the proposed park boundary and has not been acquired by Parks Canada. This land is currently grazed by cattle. Some records are also from land managed by Parks Canada in the East Block. Available habitat has likely been stable in Saskatchewan since the land acquisition for Grasslands National Park began in 1980s (Parks Canada Agency 2017).

Biology

The majority of the biological knowledge specific to the Canadian population of Greater Short-horned Lizard is available through the extensive research conducted by G.L. Powell and A.P. Russell and related work conducted by J. James, at the University of Calgary. Numerous research topics have been investigated by this core team of researchers, including diet (Powell and Russell 1984), growth and dimorphism (Powell and Russell 1985a), thermoregulation (Powell and Russell 1985b), thermoregulation related to parturition (James 1997), parturition and clutch characteristics (Powell and Russell 1991b), movement (Powell and Russell 1993), and hibernation (Powell and Russell 1994, 1996). Although this research was conducted exclusively in Alberta, it is considered applicable to Greater Short-horned Lizard throughout its Canadian range.

Life cycle and reproduction

Spring emergence occurs around mid- to late April or early May (Laird and Leech 1980), with courtship and mating from mid- to late May (James 1997). Powell and Russell (1994, 1996) recorded emergence as early as April 1st for males. After emergence, females move to individual feeding areas and become somewhat sedentary, with intermittent shifts amongst relatively small feeding areas (Powell and Russell 1993, 1994; James 1997). Males likely roam more widely in spring to seek receptive females (Henke and Montemayor 1998). The receptive period for mating is relatively short, approximately one week or less (Montanucci and Baur 1982; James 1997).

Females are sexually mature following their second winter, while males are mature after their first winter (Powell and Russell 1985a, 1991b). It is estimated that females may live up to five years, but male longevity remains unclear (Powell and Russell 1985a). Approximate age categories may be determined by the snout-vent length (SVL) of individuals, with young-of-the year (late July onward) 22 to 37 mm, yearlings 31 to 46 mm, and adults ≥ 46 mm in SVL (Powell and Russell 1985a). Age of adult lizards cannot be determined from body size. The generation time, or the average age of parents of current newborns, is probably 3 to 4 years.

Some surveys have found drastically skewed sex ratios for adult lizards. In the extensive surveys in Alberta in 2001, adult males comprised only 15.8% of all adult captures, while adult females represented 84.2% (James 2003). More recent surveys in Alberta have found a much more balanced sex ratio (FWMIS 2016). From 2004 to 2014, 143 adult lizards were recorded in the FWMIS database. Of the adult captures, males comprised 32%, females 53%, and unknown sex 15%, similar to sex ratios observed in Saskatchewan (K. Ellingson unpubl. data 2010; FWMIS 2016). Differences in detectability between the sexes may also contribute to the observed skewed sex ratios.

Greater Short-horned Lizard is one of six species of Phrynosoma that are viviparous with females giving birth to live young rather than laying eggs (Stebbins 2003). Parturition generally occurs annually in late July or early August (Powell and Russell 1991b; James 1997). It is unknown whether females are able to reproduce every year. The reproductive toll on females is significant as females weigh roughly half of their pre-parturition body mass and appear gaunt (Goldberg 1971; Powell and Russell 1991b, 1993, 1994; James 1997). However, females recuperate their body mass prior to hibernation (Powell and Russell 1994, 1996). Sex ratios of neonates are approximately even, with recorded clutch sizes varying from 6 to 14 young (Powell and Russell 1991b, 1998; UAMZ record #131; D. Whiteside personal communication 2009). The average weight of neonates is 0.7 g and average SVL is 24 mm (Powell and Russell 1991b). Neonate survival is likely low; Powell and Russell (1991b) found that only about 7% were recaptured the following year, compared with 9% of older lizards. Following parturition, females provide no post-natal care and may move a considerable distance from the natal area (Powell and Russell 1991b; James 1997). Activity diminishes in mid-September (Laird and Leech 1980; Powell and Russell 1991a, 1992a), although given appropriate weather conditions, activity has been observed as late as November (Powell and Russell 1994, 1996).

During fall, the lizards locate shallow burrows, which they may or may not dig themselves (Powell and Russell 1993, 1994; Mathies and Martin 2008). Powell and Russell (1996) found that overwintering sites were often located in sheltered areas of lower slopes, where drifting snow may accumulate and provide insulation from low winter air temperatures. Although more than one lizard may occupy a burrow, this is not typical. The burrows are relatively narrow (2 to 3 cm wide) and shallow (approximately 10 cm below the surface). Individuals enter hibernation between September and mid-November (Powell and Russell 1994).

Physiology and adaptability

Greater Short-horned Lizard is ectothermic but capable of activity at unexpectedly low temperatures given adequate solar radiation; the lizards may be active even after sunset if latent heat is adequate (J. James pers. obs.). Morning emergence is considered temperature-independent, whereas the pattern of diurnal activity is in response to temperature through behavioural thermoregulation (Heath 1962, 1965). Horned lizards that have buried themselves overnight may protrude their heads to facilitate warming of the brain prior to full emergence (Heath 1964). Short-horned lizards prefer body temperatures of 35 ºC under laboratory conditions (Prieto and Whitford 1971), and similar mean body temperature (35.8 ºC) was documented for reproductive females in the field in Alberta (James 1997). Diurnal body temperature is maintained by shuttling between sun and shade, and when no direct sunlight is available, by absorption of heat from a warm surface (Heath 1964, 1965). Alberta lizards have been documented to tolerate a broad range of body temperatures (Powell and Russell 1985b; James 1997).

Dispersal and migration

Greater Short-horned Lizard is small and slow-moving. Movements are probably hindered by dense ground vegetation and by water bodies. There is some evidence that males travel greater distances than females (Henke and Montemayer 1998), but Powell and Russell (1996) found no difference between male and female home range sizes. The longest recorded linear movement of a female lizard was approximately 310 m (July 9 – October 26, 2009) (K. Ellingson unpubl. data 2009). The total sum of the distances moved by this individual was a minimum of 1,520 m during this period (K. Ellingson, unpubl. data 2009). Generally, the lizards seem to have home ranges within which they move among smaller centres of activity over the active season (Powell and Russell 1994, 1996). The estimated median home range area of Greater Short-horned Lizard, from minimum convex polygon estimates, was 601 m², ranging from 18 to 4200 m² (Powell and Russell 1996). This estimate is based on observations from mid-summer to late fall; therefore, the home ranges for individual lizards over an entire active season could be considerably larger if initial spring movements were taken into account (Powell and Russell 1996). Not enough males were observed to directly compare home range estimates for males and females (Powell and Russell 1996).

There is evidence of seasonal shifts from summer home ranges to hibernation areas (Powell and Russell 1994). This movement to and from hibernation areas may constitute the greatest distance travelled during the lizards’ seasonal activity (Powell and Russell 1996; ASRD 2004). In one example, a female lizard moved more than 266 m over one week prior to hibernation (ASRD 2004). In Grasslands National Park, a female lizard moved 185 m in one day prior to hibernation, while no significant seasonal movement was observed in other females in the same area (K. Ellingson unpubl. data 2009). Very little is known of the dispersal movements of any size class. Movement patterns of neonates or juveniles are especially poorly known owing to their small size and the resulting difficulty in tracking them.

Interspecific interactions

Unlike some other species of Phrynosoma, Greater Short-horned Lizard is not entirely reliant on ants as a food source. In Alberta, it is a generalist insectivore that eats an array of available arthropod prey (Powell and Russell 1984).

Greater Short-horned Lizard is likely a minor prey item for numerous prairie carnivores. Eastern Yellow-bellied Racer (Coluber constrictor flaviventris) was observed attempting to swallow a male Greater Short-horned Lizard in the West Block of Grasslands National Park (K. Ellingson pers. obs. July 2010). Impaled lizards have also been observed on the perimeter barbed-wire bison fence in the West Block Grasslands National Park, presumed predated by Loggerhead Shrike (Lanius ludovicianus excubitorides; Cairns et al. 2017). In 2018 in the West Block of Grasslands National Park, an adult female was killed and partially eaten, apparently by a corvid, and an additional adult female appeared to have survived attempted predation by a Northern Grasshopper Mouse (Onychomys leucogaster) (K. Cairns personal communication 2018).

Population sizes and trends

Sampling effort and methods

Three surveys have been conducted that can be used to estimate abundance (James 2002; Fink 2014; Welsh et al. 2015). All surveys used the same search technique. Searchers examine the ground directly in front of themselves and walk at a relaxed pace (2 to 3 km/h), usually with a walking stick to probe vegetation back and forth across suitable habitat with each pass a minimum of 2 m from the last strip searched. In Alberta, sampling effort has been recorded as the number of hours searched (James 2002; ASRD 2004). In Saskatchewan, sampling effort has been recorded as linear distance searched (measured by a GPS tracklog), rather than by estimating the time spent surveying as for the Alberta surveys (Fink 2014; Welsh et al. 2015).

In the 2001 survey in Alberta, all four habitat areas were sampled. A total of 291.5 hours was spent actively searching for lizards, covering approximately 122 ha (James 2002).

In Saskatchewan, a survey was conducted in 2010 within the 2007 boundary of the West Block of Grasslands National Park. Approximately 650 km (130 ha) was searched (Fink 2014). Additional effort in 2015 included newly acquired land in the West Block of Grasslands National Park (2014 boundary). A single surveyor, following the search methodology in James (2002, 2003) and recording tracking distance searched as in Fink (2014), searched approximately 400 km (80 ha) (Welsh et al. 2015; Ellingson 2016). A recent survey of the 2007 boundary of the West Block of Grasslands National Park (7 June – 28 August 2018) and the newly acquired land (17 June – 30 August 2018) was conducted following the same survey methodology as in Fink (2014). A total of 384 km within the 2007 boundary and 120 km within the newly acquired land were surveyed.

Abundance

In the US, Phrynosoma species are regarded as “rather uncommon” even where they do occur (Pianka and Parker 1975). In Alberta, densities are generally low (Powell and Russell 1991a). A range from 1 to 2 adults detected/ha is typical for both Alberta and Saskatchewan populations (James 2003; ASRD 2004; Fink 2014), although lower densities are sometimes documented (Ellingson 2016).

Alberta

The only estimate of abundance available for Alberta is based on the 2001 survey data (James 2002) with details of the analysis provided in COSEWIC (2007). First, adult lizard densities were estimated based on survey encounter rates. Second, estimates of available and occupied habitat were made. Lizard density and amount of habitat were used to estimate abundance for each habitat area. Lizard density was estimated based on the time spent searching, the area searched, and the number of lizards encountered. The total time actively spent searching was 291.5 hours (James 2003). During the survey, 125 lizards were observed, of which 57 were adults (45.6%, based on SVL ≥ 46 mm) (Powell and Russell 1985a). Individuals were temporarily marked to avoid counting the same individual twice (James 2002). The total area searched was estimated by assuming that a searcher covered a swath approximately 2 m wide at a speed of 2.1 km/h. From this, the total area searched was estimated to be 1.22 km² (122 ha). The density estimate was approximately 1 lizard/ha. When only surveys where lizards were encountered were included, the density estimate increases to 2 lizards/ha (COSEWIC 2007). If only adult lizards are considered (45.6% of all lizards encountered), the density estimate is 0.912 adults/ha.

Habitat was considered confined to 68 sections (176.12 km²) (COSEWIC 2007). On any given section of land, approximately half was considered suitable lizard habitat, yielding an estimate of 88.06 km² of suitable habitat. A minimum estimate of population size was calculated assuming that all adult lizards present were detected (100% detectability), and that two-thirds of suitable habitat was unoccupied (as two-thirds of sections of land with apparently suitable habitat searched did not yield a lizard observation; Table 2a). A maximum estimate of population size was calculated assuming that half of individuals present were detected (50% detectability), and that all suitable habitats were occupied. The minimum adult population size was estimated to be 2,677 and the maximum 16,062 (see COSEWIC 2007 for assumptions and details of the calculations). COSEWIC (2007) gave a maximum of 16,379, but this appears to have been a miscalculation (Table 2b).

^a Forty Mile Coulee was not included in analysis, because it was considered extirpated at the time (see Fluctuations and Trends); however, recent observations indicate it is extant.

COSEWIC (2007) also estimated an effective population size due to the skewed sex ratio in the observations from the 2001 survey. The skewed sex ratio was assumed to be representative of the population. However, similarly skewed sex ratios have not been encountered in other surveys in the same habitats and are not typical of surveys for the species (see Life Cycle and Reproduction).

Estimations of abundance based on encounter rates and occupied habitat should be viewed as tentative, owing to the many assumptions that have been incorporated. Sources of error in estimating lizard density may arise from unknown detection rates, inappropriately recorded time spent searching, and variance in walking speeds among individual searchers. Estimates of total area of available habitat may also be inaccurate, as the assumption that half of each section included in the analysis contains suitable lizard habitat is based on inference and not determined empirically.

Saskatchewan

A large-scale survey of the West Block of Grasslands National Park conducted in 2010 was used to estimate abundance by estimating lizard density in various ranked habitat types (Fink 2014). First, lizard habitat within the West Block (2007 boundary) was modelled using a resource selection function (RSF) based on occupied (with lizard occurrences) and available environmental descriptions of the study area (Thomas and Taylor 1990; Manly et al. 2002). The study area was partitioned into four RSF bins, each representing habitats with increasing levels of selection (used more than would be expected based on availability; Fink 2014). Survey transects (2 m wide) were intersected with the RSF bin to calculate total search effort (area searched) per bin. The density of lizards in each bin was calculated by dividing the number of lizards observed in that bin by the area searched. A spatial mask was used to exclude non-habitat areas (roads, Frenchman River, and cultivated fields) from the map of classified RSF bins. The habitat-based index of population size was estimated as the sum of the product between total area of each RSF bin (minus the area of the spatial mask) and bin-specific lizard density (Fink 2014).

Following an update survey for the newly acquired lands in the West Block of Grasslands National Park in 2015 (Welsh et al. 2015), a new RSF habitat model was built including newly acquired land, following the methods described above (Welsh et al. 2015; Ellingson 2016; Figure 7). Encounter rates reported in Welsh et al. (2015) were not used to estimate population size due to the extremely small sample size (9 mature individuals SVL ≥ 46mm). Rather, observations from the 2010 survey (mature individuals) were used to estimate lizard density in each habitat bin (K. Ellingson unpubl. data 2010). Based on this RSF model, abundance within the West Block of Grasslands National Park was estimated to be 16,300 mature individuals (Table 3).

Sources of error in the subpopulation sizes based on RSF models are numerous. The two largest sources of error are discussed here. First, it is assumed that all lizards present along the search transects were detected. A pilot study in Grasslands National Park suggests that detection is close to 50% and varies greatly among observers (K. Ellingson unpubl. data 2009). If detection probability is low, the abundance estimates given here are much less than true subpopulation size. Secondly, the model-based estimate assumes that all suitable habitat is occupied. Surveys confirmed occupancy in most patches of good habitat, but some isolated patches may be unoccupied. Errors arising from this assumption inflate the abundance estimate. If abundance is initially estimated to be 16,000 (Table 3), and the impact of both of these sources of error are accounted for, the true subpopulation size may be as small as 8,000 (assuming detectability = 100%, habitat occupancy = 50%), or as high as 32,000 (assuming detectability = 50%, habitat occupancy = 100%) (K. Ellingson unpubl. data 2009).

^a Habitat within the study area was classified into four bins in order of increasing habitat selection by Greater Short-horned Lizards. Areas predicted to have low habitat suitability (bin 1) were used by lizards less than expected based on availability on the landscape. Areas predicted to have high habitat suitability (bin 4) were used by lizards much more than expected. See Figure 7 for a representation of habitat bins on the landscape.

All RSF models extrapolated to the East Block of Grasslands National Park had extremely poor predictive power (Ellingson 2016), and no estimate of abundance is available for this subpopulation. Abundance is likely less than estimated in the West Block given the relatively small occupied area and lower observed density (Powell et al. 1998).

Fluctuations and trends

Estimates of abundance are crude and based on infrequent surveys. Subpopulation sizes may fluctuate more rapidly than can be detected with the frequency of the surveys. Annual weather fluctuations may have pronounced effects on the population size, especially if an extreme weather event occurs during sensitive periods, such as mating or parturition (Powell and Russell 1991b). Ongoing occupancy is likely the most important variable to monitor.

Alberta

The overall capture rate in 2001 and 2002 surveys in Alberta was 2.3 h/capture (James 2002; 2003), which is similar to Powell’s previous experiences in the early 1990s (2 to 3 h/capture; G.L. Powell personal communication 2006 cited in COSEWIC 2007), suggesting roughly stable population density in occupied habitat from the mid-1990s to the early 2000s. However, some degree of overall decline was believed to have occurred because the 2001 and 2002 surveys failed to locate lizards in previously occupied areas (that is, in Forty Mile Coulee and near Medicine Hat). While no range-wide survey has been repeated since the early 2000s, numerous localized surveys have reconfirmed occupancy at sites with no or few observations in 2001 and 2002 (FWMIS 2016; S. Robertson personal communication 2016; Figure 2), indicating that many areas continue to be occupied.

Surveys in 2001 and 2002 of the South Saskatchewan River habitat area found numerous individuals near the South Saskatchewan River north of Bow Island and at a single locality between Bow Island and Medicine Hat (FWMIS 2016; Figure 2). Recent surveys confirmed occupancy at Bow Island (S. Robertson personal communication 2016). Surveys have been conducted near historical observations between Bow Island and Medicine Hat, but no lizards have been observed (S. Robertson personal communication 2016). This indicates that density is either very low or the area is no longer occupied. Records in the Medicine Hat/Redcliff portion of the South Saskatchewan River habitat area (1930s, 1950s, 1960s, 1980s, 2000) have not been recently confirmed. It is likely that the subpopulation in this area is extirpated. Subpopulations north of Medicine Hat, at the northern range extent in Alberta, were not located in the surveys in 2001 and 2002 surveys, but recent observations in this area confirm continuing occupancy (2010 –2015) (FWMIS 2016). Overall, occupancy in South Saskatchewan River habitat area had likely declined between 2000 and 2016 (Table 4).

^a Area estimates for Alberta subpopulations are based on James (2002) and COSEWIC (2007) (see Abundance), with a total habitat area in Alberta of 8800 ha. Occupied habitat area identified in Didiuk et al. (2017) was used to estimate area of habitat in the West and East blocks of Grasslands National Park.

^b Calculated from the median population estimate for each subpopulation.

In Chin Coulee, ongoing occupancy has been confirmed along the eastern and western portion of the north side of the coulee. Observations on the south side of the coulee (1991) have not been recently confirmed (FWMIS 2016). The surveys in 2001 and 2002 failed to find lizards in Forty Mile Coulee (James 2003). At the time, the construction of an irrigation dam was thought to have destroyed lizard habitat. In surveys conducted from 2007 to 2016, occupancy has been confirmed at all historically occupied localities, indicating that the subpopulation in Forty Mile is stable (FWMIS 2016). Overall, occupancy in the Chin Coulee/Forty Mile Coulee habitat area has likely declined slightly from 2001 to 2016 (Table 4).

The surveys in 2001 and 2002 confirmed a large subpopulation in the Manyberries Hills habitat area (James 2002, 2003). Occupancy has been recently confirmed throughout the Manyberries Hills habitat area, with numerous observations where the 2001 to 2002 survey located lizards, as well as several kilometres farther south, both in historically occupied areas and in previously undocumented areas (FWMIS 2016; S. Robertson personal communication 2016). Three localities have been identified south of Township Road 50, expanding the presumed occupied habitat in the Manyberries Hill habitat area. No observations in the immediate vicinity of the hamlet of Manyberries have been made since the 1970s (FWMIS 2016; Figure 2). The occupancy is consistent with what was observed by G.L. Powell, with some increase due to the new records indicating that the subpopulation is likely stable (Table 4).

The surveys conducted in 2001 and 2002 failed to find lizards in many historically occupied habitats in the Milk River habitat area, which was unexpected given the apparently suitable habitat (James 2002, 2003). Numerous observations from 2005 to 2016 confirmed continued occupancy in both the eastern and western portions of the Milk River habitat area; however, some localities along the eastern portion along the Milk River proper observed in the 1960s – 1980s have not been confirmed recently (FWMIS 2016; S. Robertson personal communication 2016) (Figure 2). The central portion of the Milk River habitat area has only a single observation from 1923 (FWMIS 2016). Continuing occupancy of this area is unconfirmed. Occupancy along the Milk River likely remains stable (Table 4).

Saskatchewan

For the Saskatchewan subpopulations in the West Block of Grasslands National Park, surveys in 1995 and 2010 indicate that the number of individuals is steady or increasing. In the West Block, Powell et al.(1998) captured 41 lizards (2 adults, SVL ≥ 46 mm) in 15 days of surveying. In 2010, 116 lizards were captured (101 adults, SVL ≥ 46 mm) in 652 km of search transects (the 2010 survey was mostly conducted early in the season before parturition), resulting in an encounter rate of 0.15 adult lizards/km. For comparisons with the 2010 data, the same areas of the West Block were surveyed from 7 June to 28 August 2018. A total of 384 km was surveyed using Fink's (2014) method, and 86 lizards (42 adults with SVL≥46 mm, 21 older juveniles, 23 young of the year) were detected (N. Cairns personal communication 2018, 2019). The total lizard density was calculated as 0.22/km and the adult density as 0.11/km. While calculated densities are not easily comparable between the survey conducted in 1995 and those in 2010 and 2018, the data suggest that the subpopulation has remained relatively stable over the past two decades.

In the 2015 survey of newly acquired land in the West Block, 21 lizards (9 adults, SVL ≥ 46 mm) were captured in 399 km of transects, resulting in an encounter rate of 0.02 adult lizards/km (Welsh et al. 2015). This indicates an 87% reduction in the encounter rate compared to the 2010 survey (0.15 adult lizards/km; Fink 2014). It is unclear whether the different encounter rates are due to differences in lizard densities in adjacent areas of the West Block, differences in search conditions that would alter detectability, or an alarming reduction in lizard densities in the time between the two surveys. Observers in both surveys were experienced, and surveys were restricted to weather conditions generally considered suitable for detecting lizards (Fink 2014; Welsh et al. 2015).

To examine these options, the 2015 survey was repeated, and the same newly acquired land was resurveyed using the same methods from 17 June to 30 August 2018 (N. Cairns personal communication 2018, 2019). A total of 120 km were surveyed, and 19 lizards (4 adults with SVL≥46 mm, 10 larger juveniles, 5 young of the year) were detected. The total lizard density was calculated as 0.16/km and the adult density as 0.03/km. These values are considerably lower than original estimates generated in 2010 but higher than those in 2015. The reason for the extremely low values in 2015 is unclear and may relate to habitat quality, population fluctuations, survey/detectability biases, or a combination of all three.

In the East Block of Grasslands National Park, surveys in 1995 and 1996 were the only large-scale effort in occupied lizard habitat (Powell et al. 1998). Capture rates were 20 h/capture in 1995 and 12.5 h/capture in 1996 (Powell et al. 1998). Powell et al. (1998) found lizards in a much larger area of the East Block than has been located in any survey attempt since that time, although no survey has attempted to cover the exact same areas searched by Powell et al. 1998 (H. Facette personal communication 2016). Welsh et al. (2015) were able to confirm occupancy in one small area of the East Block, but most occupied sites have been unconfirmed since the initial survey of the area. The subpopulation in the East Block has not been sufficiently targeted in recent surveys to determine trends in occupancy or subpopulation size.

Extreme fluctuations

Repeated surveys of the same areas indicate that the number of mature individuals may fluctuate greatly among years, but it is uncertain whether such fluctuations are extreme (that is, an order of magnitude) and whether they occur synchronously over large areas. An example of fluctuations is from the West Block and adjacent newly acquired lands in Grasslands National Park, where the number of adult lizards per km surveyed fluctuated from a high of 0.15 in 2010 to a low of 0.02 and 0.03 in 2015 and 2018 (see details above). Large multi-annual fluctuations have been also noted in Alberta (Powell and Russell 1992; James 2002), but differences in survey effort among years preclude accurate estimation of their magnitude. The fluctuations may reflect poor survivorship or reproduction success due to prolonged droughts and associated reduction in prey availability in some years (Powell and Russell 1992) or high overwinter mortality driven by weather and snow conditions. A complicating factor is the sensitivity of the lizards to weather conditions during surveys, which may affect their detectability and bias the results. Although possible, the currently available information is insufficient to ascertain whether the Great Short-horned Lizard population undergoes extreme fluctuations.

Summary

Overall, the population size of Greater Short-horned Lizard in Canada has likely declined, especially from the time of initial agricultural development early in the 20th century until the J. James surveys (2001 to 2002). More recent declines are evident in local areas, particularly near Medicine Hat. In other instances, lack of recent records may be related to lack of survey effort and not reflect true declines in population size or occupancy. In these instances, trends in subpopulation size are unknown. The inferred trends of subpopulation size in Alberta are summarized by habitat area in Table 4.

Population fragmentation

The Canadian population of Greater Short-horned Lizard is fragmented into six subpopulations in remnant prairie habitat associated with rugged coulee slopes unsuitable for cultivation. While habitat loss is largely historical, habitat modification by invasive plants and human activities continues. The historical loss of one small subpopulation near Grassy Lake and apparent declines in a portion of another subpopulation in recent times near Medicine Hat are indicative that the subpopulations are not secure. For severe fragmentation to apply, most of the Canadian population is to be within habitat fragments that are smaller than expected to support a viable subpopulation. If fragmentation is considered at the scale of the six habitat areas, then the population is not severely fragmented, although the habitat areas are isolated from one another by distances that exceed the movement capabilities of the lizards. Within the habitat areas approximately 90% of the population is considered stable or increasing (Table 4). The habitat within the six habitat areas is patchy, but this patchy distribution is characteristic of the preferred habitat type and typical of the distribution pattern of this species.

Rescue effect

For the subpopulation along the Milk River, there is possible connectivity with occupied habitat in Montana. A record from 2008 at the north end of the Fresno Reservoir in northern Montana is 26 km from the nearest Canadian record. Both of the observations are from the Milk River drainage. Habitat appears to be continuous along the drainage between the two observations, and suitable habitat was predicted by an inductive model produced by Montana Natural Heritage Program (MNHP 2016a). No other Alberta subpopulations are in close proximity to recent observations in Montana (FWMIS 2016; MNHP 2016b).

For the subpopulation along the Frenchman River in the West Block of Grasslands National Park, there is possible connectivity with subpopulations in Montana. The habitat south of the international border appears suitable for Greater Short-horned Lizard. The nearest record in Montana is approximately 22 km south of the southernmost observation in the West Block. Both observations are in the Frenchman River Valley (Fink 2014; MNHP 2016b). Similar connectivity is not evident for subpopulations in the East Block. The nearest Montana record is approximately 56 km south of lizard observations in the East Block, and limited suitable habitat is available between the two observations (Welsh et al. 2015; MNHP 2016b).

With the exception of subpopulations in the Milk River habitat area and the West Block of Grasslands National Park, rescue from populations in the United States is unlikely given the large distances relative to the limited dispersal ability of Greater Short-horned Lizard.

Threats and limiting factors

Threats

Globally, declines in reptile populations are linked primarily to habitat loss, along with a host of other threats, the majority of which are anthropogenic in nature (Böhm et al. 2013). Powell and Russell (1991b) suggested that Greater Short-horned Lizard is “probably extremely sensitive” to human-caused stresses. In Canada, Greater Short-horned Lizard faces numerous threats associated with urbanization, tourism infrastructure and activities, agricultural activities, oil and gas drilling, and climate change. These threats contribute to the loss, degradation, or fragmentation of habitat and/or cause direct and indirect mortality. Due to the inability of Greater Short-horned Lizard to disperse great distances, habitat loss and degradation likely contributes indirectly to mortality. Not all threats discussed here are equally applicable across the entire Canadian range.

The IUCN Threats Calculator was applied to Greater Short-horned Lizard by a panel of experts. The overall threat impact was assessed as “medium”, based on four main threats (Appendix 4). A medium impact rating implies a 3 to 30% projected reduction in the population size over the next three generations from threats operating over the next ten years. The applicable threats are discussed below by IUCN standard threat categories in their approximate, perceived order of importance.

Other ecosystem modifications (threat impact medium)

Vegetation structure is an important characteristic of Greater Short-horned Lizard habitat (James 1997; Fink 2014). Invasive plant species may cause negative changes in otherwise suitable habitat. Some invasive plants, such as Downy Brome (Bromus tectorum), have been found to negatively impact horned lizards by altering the structure and composition of the plant community and impeding movements (Newbold 2005). Although Downy Brome has not yet invaded any Greater Short-horned Lizard habitat in Canada, the plant does occur in both Alberta and Saskatchewan and is an impending threat. Another invasive plant already present in Greater Short-horned Lizard habitat in Canada is Yellow Sweet-clover (Melilotus officinalis). It is a threat to grasslands because it can spread rapidly in open areas and can out-compete native species and alter the species composition, soil chemistry, and ecosystem processes (Wolf et al. 2003). The plants can tolerate a wide range of environmental conditions, including droughts, and can grow up to 90 to 300 cm in height, often forming dense patches (Wolf et al. 2003). Nitrogen-fixing invasive species such as Yellow Sweet-clover can increase soil nitrogen, which in turn may facilitate the invasion of other exotic plants in sparsely vegetated badland systems (Van Riper and Larson 2009).

Yellow Sweet-clover is present in the Manyberries Hills and in the West Block of Grasslands National Park. Varying densities of Yellow Sweet-clover has been documented from several localities occupied by the lizards in Grasslands National Park. Given the longevity of the seeds (seeds may remain viable for decades), the ability of the plant to grow on most soil types, and the continued use of sweet clover by farmers as green manure in areas surrounding the Park, this plant will likely continue to expand its distribution and pose a threat to the integrity of the grassland ecosystem (M. Sliwinski personal communication 2018).

Invasive plants, particularly Yellow Sweet-clover, have been observed in occupied habitats in both Alberta and Saskatchewan, and the threat is considered to have a large scope. The severity of this threat is expected to be moderate, but there is uncertainty. Overall, the threat is considered to have a medium impact on the population.

Climate change & severe weather (threat impact: medium – low)

Climate is considered the primary constraint on the range of Greater Short-horned Lizards at their northern range periphery in Alberta and Saskatchewan (Powell and Russell 1991a,b, 1996). Climate change models predict increases in temperatures in the prairie grasslands but cannot predict changes in climate variability (Barrow 2009), which is the aspect of climate change most likely to negatively impact Greater Short-horned Lizard. Warmer summers could extend the active season, resulting in enhanced body condition and increased recruitment. However, if climate change brings more extreme cold weather events accompanied by reduced snow cover, survival during hibernation may be reduced (James 1997; ABMI 2016). Other drastic inopportune weather events, such as heavy rains during parturition, could eliminate recruitment in some areas and years. Prolonged drought in the 1980s may have diminished arthropod populations and led to the apparently reduced lizard population levels recorded by Powell and Russell (1992a).

Shank and Nixon (2014) assessed the impacts of climate change on Greater Short-horned Lizard in Alberta by the 2050s. They found that the species is highly vulnerable to climate change, based on a combination of its high sensitivity and exposure (Shank and Nixon 2014). While higher temperatures were considered beneficial for the species, reductions in overwinter snow accumulation and increased frequency of drought were considered to have negative impacts (ABMI 2016). The lizards’ restricted distribution and their limited ability to disperse to more suitable habitats as the climate becomes unfavourable contributed to their vulnerability (ABMI 2016).

The scope of the threat was assessed as pervasive and the severity as slight – moderate, reflecting uncertainty regarding future climatic conditions, particularly the magnitude of changes in seasonal temperature and precipitation patterns over the next 10-year period and the responses of the lizards to the changes.

Energy production and mining (threat impact low)

Activities associated with oil and gas drilling contribute to habitat disturbance and loss and may also result in mortality during construction. Within the four occupied habitat areas in Alberta, there are approximately 3,300 well sites (Table 5; AER 2016). Densities are highest within the South Saskatchewan River and Milk River and tributaries habitat areas (AER 2016) (Table 5). There are no active oil or gas developments in the Saskatchewan portion of the range (Environment Canada unpubl, data in Environment Canada 2015). A cumulative effects assessment estimated that approximately 15% of available lizard habitat was potentially influenced by development features, such as wells, access trails, and pipelines in the Manyberries area (Kissner 2005). The available habitat measure used in the assessment is not equivalent to the area of occupation, as it is not restricted to areas with records of Greater Short-horned Lizard (Kissner 2005).

Oil and gas resource development activities, such as exploration (for example, seismic lines, seismic tests), construction (for example, roads, pipelines, facilities, power lines, staging areas – assessed under Transportation), operations (for example, drilling, compressor stations), decommissioning, and reclamation, all contribute to habitat disturbance in Greater Short-horned Lizard habitat. These activities contribute to soil erosion, which negatively impacts hibernation habitat quality (Bradshaw et al.1995). Soil structure is damaged by soil stripping during construction, soil compaction by heavy machinery, and possible localized soil contamination.

Direct mortality may occur if Greater Short-horned Lizard is attracted to well pads, perhaps due to thermally advantageous slopes associated with the raised bed or berms. Lizards on well pads are at risk from vehicle traffic (J. James personal communication 2012 in Environment Canada 2015).

Overall, oil and gas drilling are considered a continuing threat of restricted scope. Expected severity of the threat is slight, contributing to a low overall impact on the population.

Agriculture (threat impact Low)

Agriculture is the primary human land use in southeastern Alberta. Past cultivation likely eliminated connectivity between disparate pieces of occupied habitat. Generally, the remaining steep slopes of the habitats that Greater Short-horned Lizard occupies are unsuitable for cultivation, therefore cultivation and habitat conversion into annual cropland or forage crops is considered a relatively minor threat in the future. However, some habitat near coulee edges may be at risk to cultivation (Didiuk et al. 2017). Where cultivation occurs, it is likely to eliminate suitable habitat and cause high direct mortality. Cultivation adjacent to occupied coulee slopes results in the loss of some foraging and dispersal habitat, as the lizards are known to forage in the 100 m adjacent to occupied badlands (Didiuk et al. 2017). Cultivated fields or dense crops likely act as a barrier to movement for horned lizards (Newbold 2005).

Conversion of native habitat to cropland is a threat with a small scope due to soil and terrain limitations for crop and forage production near the majority of lizard habitat. However, this threat is considered continuing and of serious severity. Overall, the threat impact is considered low.

Human intrusions and disturbance (threat impact Low)

Off-road vehicles, such as all-terrain vehicles (ATVs), motorcycles, and trucks, are popular in the rugged terrain typical of Greater Short-horned Lizard habitat. These activities are anticipated to have harmful effects on Greater Short-horned Lizard populations in Canada, both by way of habitat disturbance and direct mortality of individuals (James 1997; ASRD 2004). Off-road vehicle use in dune habitat has negatively impacted horned lizards in California (Beauchamp et al. 1998). The use of dirt bikes and ATVs in occupied habitat has been observed to cause significant localized habitat damage (James 1997). Recreational activities are considered to have a small scope, but to have extreme to serious severity where they occur. Overall, the impact on the population is considered low.

Invasive and other problematic species (threat impact Low)

Predation risk may increase when predators are attracted to human developments in occupied habitat (Anonymous 1949; Tyler 1977; Sherbrooke 1991; James 1997). In particular, the above-ground anthropogenic structures may be used by avian predators as perches (L. Powell personal communication 2012 in Environment Canada 2015). Black-billed Magpie (Pica hudsonia) and American Crow (Corvus brachyrhynchos) densities increase in native grasslands when anthropogenic structures are present (Quinlan 2013). It is likely that predation pressure on Greater Short-horned Lizard populations increases in habitats with anthropogenic structures. Increase in predation risk is considered to have a restricted or small scope and to have a moderate impact where it occurs. The threat is continuing and likely has a low impact on the population.

Threats with Unknown impacts

Agricultural & forestry effluents

Spray drift (such as from grasshopper pesticides) may decrease prey availability for Greater Short-short horned Lizard in adjacent habitat. Runoff of fertilizers may increase soil fertility in adjacent coulees, possibly increasing vegetation growth. Changes in vegetation structure or species composition may negatively impact mobility (see ‘Other ecosystem modifications’). The impact of this threat is unknown due to the unknown severity of the threat on the population.

Threats assessed as Negligible

The following threats were assessed as negligible in overall impact for the Canadian population of the lizard at present but could be locally important: Dams & water management/use, Mining & quarrying, Roads & railroads, Housing and urban areas, Tourism & recreation areas, Hunting & collecting terrestrial animals, Renewable energy, and Work & other activities (see Comments column in Appendix 4 for details). While the impacts of these activities are deemed negligible for the Canadian population as a whole, they may still be locally significant.

Limiting factors

Ability to tolerate a wide range of body temperatures, as indicated by a long active season extending to sub-freezing conditions, has enabled Greater Short-horned Lizard to survive in northern habitats, where it experiences a relatively short active season and considerable climatic variation (Powell and Russell 1996). However, high levels of mortality in late fall and over winter might be one of the determining factors in the altitudinal and latitudinal limits for this species in Canada (Powell and Russell 1994, 1996). The lizards may be particularly vulnerable to sudden temperature drops or to predators just prior to hibernation, due to their tendency to remain above surface while attempting to take advantage of warm, late fall weather (Powell and Russell 1996). Using shallow burrows for hibernation may contribute to low over-winter survival rates (Powell and Russell 1996).

Greater Short-horned Lizard in Canada is probably limited by a combination of historical habitat conversion during initial agricultural development in the early 20th century and physiological and behavioural restrictions acting in conjunction with climatic barriers (Powell and Russell 1998). Over-winter survivorship, reproductive biology, and perhaps habitat requirements may all contribute to their limited range in Canada (see Physiology and Adaptability; Powell and Russell 1996, 1998).

The relative significance of these limiting factors differs between Saskatchewan and Alberta subpopulations. For Saskatchewan subpopulations, physiological and behavioural restrictions, combined with climatic barriers, are expected to be the most significant population-level constraint, as the lizards are confined within Grasslands National Park, an area of limited human impact (Powell and Russell 1996; Powell et al.1998). In Alberta, human-caused threats are more likely to play a significant role.

Number of locations

It is difficult to define locations based on threats that can rapidly affect all individuals at sites in a short period of time, as most of the threats affect the lizards incrementally and cumulatively over time. Most projected threat events are likely limited to a small spatial extent and would affect a small proportion of overall occurrences (for example, construction of an oil well lease, recreational off-road vehicle use). Many of the threats are related to land management practices and anthropogenic activities on the land; therefore, land ownership might be used as a proxy for threat-based locations. In Alberta, land ownership is a mixture of privately held leases, grazing associations, provincial natural areas, and private ownership. In Saskatchewan, the majority of land parcels are within Grasslands National Park. Some additional land parcels are provincial lease land, including Dixon Community Pasture and privately held leases within the new proposed boundary of the East Block.

Two threats, habitat modification by invasive plants and climate change, have the potential to affect a large part of the distribution of the species relatively rapidly. Based on the main threat of invasive plants, the most plausible number of locations is well over ten using land ownership as a proxy for different management regimes. Based on climate change and severe weather as a threat, the number of locations could be as low as six, corresponding to each subpopulation, which is likely to experience similar regional climate patterns. However, there is much uncertainty about the rate of change over the next 10-year period and impacts of this threat on the lizards.

Protection, status and ranks

Legal protection and status

In Canada, Greater Short-horned Lizard is listed as Endangered on Schedule 1 under the Species at Risk Act (SARA) (Government of Canada 2012). SARA defines Endangered species as wildlife species that are facing imminent extirpation or extinction. Under SARA, Greater Short-horned Lizard and its residences are protected from harm; the implementation SARA is currently focused on federal lands. It is prohibited to destroy Critical Habitat identified in a recovery strategy or action plan, a restriction currently implemented only on federal lands. Critical Habitat has been identified within the Grasslands National Park (Government of Canada 2015, 2016).

In Alberta, Greater Short-horned Lizard is listed as Endangered in Schedule 6 of the provincial Wildlife Act (Alberta Regulation 143/1997; Government of Alberta 2013). Under the Alberta Wildlife Act, listed species are protected from harm, and a recovery planning process must be initiated.

In Saskatchewan, the provincial Wildlife Act prohibits unauthorized killing, disturbance, collection, harvest, capture, sale, and export of wildlife, including Greater Short-horned Lizard, without a permit (Government of Saskatchewan 2007).Greater Short-horned Lizard is not specifically listed in the Wild Species at Risk Regulations (Chapter W-13.11 Reg 1), which offer further protection for species considered provincially at risk (Government of Saskatchewan 1999).

Greater Short-horned Lizard is not offered any legal American federal or international protection (CITES 2013; USFWS 2013).

Non-legal status and ranks

Greater Short-horned Lizard has a general status of At Risk in Alberta. This At Risk status was a precursor for its legal designation as Endangered in Schedule 6 of The Wildlife Act (Alberta Regulation 143/1997; Government of Alberta 2013). In both Alberta and Saskatchewan, a subnational rank of S2 has been assigned to the species (NatureServe 2015; Alberta Conservation Information Management System (ACIMS) 2015; Saskatchewan Conservation Data Centre (SCDC) 2015). S2 ranking indicates that the species is considered imperilled, or at high risk of extinction or elimination due to very restricted range, very few populations, steep declines, or other factors (NatureServe 2015).

In Montana, the only US state with the potential for contiguous populations with those in Canada, Greater Short-horned Lizard is listed as a Montana Species of Concern with a state rank of S3 (MNHP 2015; NatureServe 2015). Species of Concern are defined as native Montana species that are considered to be at risk due to declining population trends, threats to their habitats, and/or restricted distribution. S3 ranking indicates that at a state level Greater Short-horned Lizard is considered Vulnerable, that is, at moderate risk of extinction or elimination due to a restricted range, relatively few populations, recent and widespread declines, or other factors (NatureServe 2015).

NatureServe applies a global rank of G5 (secure, or common, widespread, and abundant) to Greater Short-horned Lizards (NatureServe 2015). The IUCN Red List assigned it the category of Least Concern (widespread and abundant; Hammerson 2007). A summary of non-legal conservation status ranks for Greater Short-horned Lizard across the species’ range is given in Table 6.

Habitat protection and ownership

Critical habitat under SARA has been partially identified as part of the federal recovery strategy for Greater Short-horned Lizard (Environment Canada 2015). A combination of a model-based approach and occurrence buffering was used to identify polygons of Critical Habitat in Saskatchewan and Alberta.

In Alberta, Critical Habitat identified in the federal recovery strategy is either privately owned or provincial crown land and has not been formally designated (Environment Canada 2015; Didiuk et al. 2017). Developments in habitat occupied by Greater Short-horned Lizard require impact assessments and impact mitigation (J. Nicholson personal communication 2016). Some occupied habitat is protected by protective notations (S. Robertson personal communication 2018). A protective notation restricts some land uses on public land.

In Saskatchewan, the vast majority of records for Greater Short-horned Lizards are within the current or proposed boundaries of the Grasslands National Park (Powell et al. 1998; Leung 2012; Fink 2014; Welsh et al. 2015). Some recent records are immediately north of the West Block boundary in a provincial community pasture, and land use to date in this area has been compatible with Greater Short-horned Lizard conservation (H. Facette personal communication 2016). However, the discontinuation of the provincial community pasture program may contribute to changes in land use in these pastures. Critical Habitat has been identified to encompass the most reliable records (Environment Canada 2015; Government of Canada 2015, 2016; Parks Canada Agency 2016). A total of 12 polygons encompassing 70.4 km² was identified as Critical Habitat in the West Block (Environment Canada 2015). In the East Block, five polygons encompassing 6.6 km² were identified (Environment Canada 2015). An additional 12.6 km² were identified following surveys by Welsh et al. (2015) in newly acquired lands in the West Block (Government of Canada 2016; Parks Canada Agency 2016).

Acknowledgements and authorities contacted

The following people were contacted to provide information in the preparation of this report. Thank you to all who generously provided information, including unpublished data.

Canadian Wildlife Service
Andrew Didiuk
Alain Filion

Parks Canada
Shelley Pruss
Heather Facette
Stefano Liccioli

Alberta Environment and Parks
Lonnie Bilyk
Sandi Robertson
Joel Nicholson

University of Calgary
Larry Powell
Magdalene Leung

Queens University
Nicholas Cairns

Saskatchewan Ministry of Environment
Jeff Keith

Saskatchewan Conservation Data Centre
Andrea Benville

Montana Natural Heritage Program
Martin Miller

Authorities contacted

Not applicable

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Biographical summary of report writers

Krista Ellingson completed her Master’s thesis on the landscape- and micro-scale habitat selection of Greater Short-horned Lizard in Grasslands National Park in 2014 with Dr. Scott Nielsen and Dr. Shelley Pruss of the University of Alberta. She currently works as an environmental consultant. Her recent work has included building predictive spatial models of lizard habitat and conducting range health assessments in community pastures. She currently volunteers as a Regional Coordinator (Zone 6) for the Saskatchewan Breeding Bird Atlas.

Collections examined

No specimens were examined.

For Alberta, the primary source of observation records was obtained from the Fish and Wildlife Management Information System database (FWMIS 2016). Additional information regarding recent observations up to and including summer 2016 was obtained from S. Robertson at Alberta Parks and Environment.

Records included in the Saskatchewan maps were obtained from the Saskatchewan Conservation Data Centre (2016), Grasslands National Park Greater Short-horned Lizard transmitter research (2008, 2009), Federal Student Work Experience Program surveys and volunteer surveys (2007, 2008, 2017), surveys by L. Powell (1995, 1996), M. Lueng (2010), K. Ellingson (2009, 2010), K. Welsh (2015), and the Royal Saskatchewan Museum (2013). H. Facette (Parks Canada) provided a list of incidental observations from Grasslands National Park’s Kestrel database.

Appendix 1. Extent of occurrence (EOO) and index of area of occupancy (IAO) based on observations from 1995 to 2017 inclusive

Appendix 2. Extent of occurrence (EOO) and index of area of occupancy (IAO) based on observations from 1991 to 2006 inclusive

Appendix 3. Anthropogenic development in the vicinity of Greater Short-horned Lizard records in Alberta

Appendix 4. Threats calculator assessment for Greater Short-horned Lizard in Canada

Threats assessment worksheet

Species or ecosystem scientific name:

Phrynosoma hernandesi

Element ID:

Not applicable

Elcode:

Not applicable

Date:

2017-04-18

Assessor(s):

Kristiina Ovaska (facilitator, Amphibians and Reptiles SSC Co-Chair), Krista Ellingson (status report writer); provincial jurisdictions: Sandi Robertson (AB), Robin Gutsell (AB); federal jurisdictions: Andrew Didiuk (CWS), Laura Gardiner (PC), Heather Facette (PC); Other: Larry Powell (University of Calgary); Amphibians and Reptiles SSC: Pamela Rutherford, Briar Howes, Tom Herman (Co-chair)

References:

COSEWIC draft report

Assigned overall threat impact:

C = Medium

Impact adjustment reasons:

The impact was reduced from “High” because a) there is much uncertainty about the population effects of the highest scoring threats (invasive plants and climate change), b) the scope for most of the other threats is at the low end of the range, and several larger subpopulations (for example, in Grasslands National Park) appear to be stable.

Overall threat comments:

Generation time of 2 to 5 years was assumed

Glossary

Impact

The degree to which a species is observed, inferred, or suspected to be directly or indirectly threatened in the area of interest. The impact of each threat is based on Severity and Scope rating and considers only present and future threats. Threat impact reflects a reduction of a species population or decline/degradation of the area of an ecosystem. The median rate of population reduction or area decline for each combination of scope and severity corresponds to the following classes of threat impact: Very High (75% declines), High (40%), Medium (15%), and Low (3%). Unknown: used when impact cannot be determined (for example, if values for either scope or severity are unknown); Not Calculated: impact not calculated as threat is outside the assessment timeframe (for example, timing is insignificant/negligible or low as threat is only considered to be in the past); Negligible: when scope or severity is negligible; Not a Threat: when severity is scored as neutral or potential benefit.

Scope

Proportion of the species that can reasonably be expected to be affected by the threat within 10 years. Usually measured as a proportion of the species’ population in the area of interest. (Pervasive = 71 to 100%; Large = 31 to 70%; Restricted = 11 to 30%; Small = 1 to 10%; Negligible < 1%).

Severity

Within the scope, the level of damage to the species from the threat that can reasonably be expected to be affected by the threat within a 10-year or three-generation timeframe. Usually measured as the degree of reduction of the species’ population. (Extreme = 71 to 100%; Serious = 31 to 70%; Moderate = 11 to 30%; Slight = 1 to 10%; Negligible < 1%; Neutral or Potential Benefit > 0%).

Timing

High = continuing; Moderate = only in the future (could happen in the short term [< 10 years or 3 generations]) or now suspended (could come back in the short term); Low = only in the future (could happen in the long term) or now suspended (could come back in the long term); Insignificant/Negligible = only in the past and unlikely to return, or no direct effect but limiting.