Greater short-horned lizard COSEWIC assessment and status report: chapter 5
Habitat
Short-horned Lizards inhabit an array of habitat types over the broad longitudinal range they occupy: 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 area Short-horned Lizards inhabit is part of the northern extremes of the Great Plains, and is located in the southernmost areas of both Alberta and Saskatchewan. In both provinces the areas concerned fall 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 the area occupied with lizards is part of the ‘Mixed Grass ecoregion’ (SCDC 2002).
Not surprisingly, the co-dominance of short- and mid-height grasses in these communities gave rise to the label “Mixed grass”. In Alberta, a community comprised of a blend of the mid-height grass Stipa comata (Spear Grass) and the short-grass Bouteloua gracilis (Blue Grama) makes up the majority of vegetation across the area’s predominantly (60%) orthic brown chernozemic soils (NRC 2006). On solonetzic soils (10%), more common in the area of the Manyberries Hills, a mixture of the mid-height Western Wheatgrass (Agropyron smithii) grows in combination with Blue Grama (NRC 2006). In Saskatchewan, the primary vegetative community in lizard-inhabited areas is the Bouteloua-Stipa assemblage (Coupland 1950). The East block is predominated by brown loamy chernozem soils (Clayton et al. 1977; SIP 1992). In the West Block, clay to clay loam brown chernozems comprise the uplands surrounding the Frenchman River valley (SIP 1992).
Low levels of precipitation, remarkable potential extremes in daily and seasonal temperatures, and significant wind levels characterize this region. Conditions favour high rates of evaporation. The mean annual precipitation in the Dry Mixedgrass subregion of Alberta is approximately 333 mm annually (NRC 2006), with wide levels of variation. Over the Saskatchewan portion of the range, average annual precipitation is 313 mm in Val Marie, the town-site nearest Grasslands National Park (Fung 1999). The majority of precipitation over the entire region generally falls during the spring and summer months (NRC 2006; Fung 1999). When significant precipitation events do occur, the greater part of the region in Alberta drains to the Saskatchewan River system, while the remainder of the area, in both provinces, flows into the Missouri River system, through the Milk River and its tributaries. In Alberta, the mean daily maximum (summer) temperatures is 26.2°C and mean daily minimum (winter) temperature is –17.7°C (NRC 2006). For Val Marie, in Saskatchewan, the daily mean temperature in July is around 18° C, whereas the daily mean temperature for January is nearer to –17°C (Fung 1999). There are between 87 - 130 frost-free days over this part of Alberta (NRC 2006) and about 80-100 frost-free days (Fung 1999) in the respective portion of Saskatchewan.
Habitat requirements
Phrynosoma hernandesi is a habitat generalist based on its wide habitat usage across its latitudinal distribution (Sherbrooke 2003). In Canada, Greater Short-horned Lizards are most commonly found on south-facing slopes along coulees, badlands and ravines. Lizards inhabit elevations from around 700 m to over 1075 m in Alberta (Powell and Russell 1993a; James unpubl. data), and between approximately 800 – 900 m in Saskatchewan (Powell and Russell 1993a).
The eroded inclines and disturbed vegetative patterns associated with the slopes of coulees provide a mix of open soil surface interspersed with vegetation. Slopes also offer good drainage and loose soils for shelter and overwintering habitat. Horned lizards often bury into the soil for shelter overnight and over winter, a practice that has been widely documented in horned lizards (Heath 1965), and observed in Alberta populations (Laird and Leech 1980; James 1997). Perhaps related to this, they seem to prefer areas with loose, sandy soils.
The presence of vegetation is also significant for lizards in Alberta, providing shade from the sun as well as overnight shelter (James 1997). In a recent population survey, the percentage of the area surrounding captured lizards that was open soil averaged approximately 52%, whereas shrubs, forbes and grasses combined, averaged about 43%, with wide variability within each category (James 2002). Too much vegetation is likely a deterrent to Short-horned Lizards, as it is anticipated to impede their movement. Thick grasses, for example, render them less able to find and capture prey, and make them more vulnerable to predators by amplifying their movements.
The habitat of Short-horned Lizards is naturally patchy. Areas along watercourses with sparsely vegetated south-facing slopes and appropriately friable soils for hibernation seem to be shared features. The availability of this habitat type varies with the position of the channel with which it is associated; east-west cut channels provide more sloped areas with southern exposure than do north-south cut channels. The area with the largest extent of potential habitat appears to be that of the Manyberries Hills. Across the entirety of southeastern Alberta, there are areas of what appears to be appropriate habitat from which the species is apparently currently absent, or has never been recorded.
Powell and Russell (1993a) divided the habitat types in which Short-horned Lizards are found in Alberta into three main categories. Generally speaking, the habitats to the north, that is, those along the South Saskatchewan River, and the Chin coulee area, can be described as one sort. The habitat type within the Manyberries Hills, southwest of the Cypress Hills, constitutes the second, and that along the Milk River and tributaries, another. In all cases, Greater Short-horned Lizards tend to favour the sparsely vegetated south-facing slopes, but are not restricted to them exclusively. They have been captured from low on the slopes, in some cases even in the bottomlands, all the way up to the nearby grasslands, which surround the ecotones with which they are more commonly associated.
The habitat along the Milk River basin tends to be along the rims of coulees and canyons, as well as the breaks affiliated with badland areas (Powell and Russell 1993a). The most westerly of these records are from the south banks of the Milk River proper just east of Writing-On-Stone Provincial Park (FWMIS 2006). The more numerous eastern records, within this location, are on the north side of the Milk River, and scattered along the Lost River basin, and as far east as the border town of Wild Horse (FWMIS 2006). The majority of these records are relatively close to the US border and the possibility exists that there may be contiguous populations in Montana, although the extent of cultivation south of the border is much wider over this entire region.
In the Manyberries Hills area, most of the valleys are wide and relatively flat. Here, the habitat is comprised of dunes, formed by the erosion of the exposed Bearspaw shale common in the area, and interspersed with mats of creeping juniper (Juniperus horizontalus). As a result, the area offers relatively wide swaths of potential habitat, with numerous microclimate opportunities available for the lizards. The juniper anchors the friable soils and thus causes a somewhat hummocky effect. These dunes, capped with juniper mats, and about 2 m across, are interspersed with largely unvegetated alluvial flats (Powell and Russell 1998). The mainly flat-topped upland areas between the wide expanses of juniper dunes are covered with typical short- and mixed-height grass species. Populations in this area appear to be more widespread with more individuals than those of other areas (James 2002; ASRD 2004).
The populations of Short-horned Lizards found along the Chin and Forty-Mile coulees and those along the South Saskatchewan River tend to inhabit the upper one third of the slopes associated with these watercourses (Powell and Russell 1998). The Chin Coulee population occurs on both the north and south banks (Powell and Russell 1998). Along the South Saskatchewan river, lizards rarely venture onto the lower, extremely sparsely vegetated slopes or up onto the more thickly vegetated surrounding grasslands (Powell and Russell 1998). Here, the favoured habitat has resulted from the erosion of the upper reaches of the channel proper, and the formation of multiple folds of coulees and slopes, all angling ultimately toward the main channel. Some of the primary coulees also possess upper, tributary coulees. The resulting complex is a mix of grades and aspects that varies widely from area to area. These populations are the most northerly of all Greater Short-horned Lizard populations in Canada. Lizards are found on the north side of the river in the western portion of the location, and on the opposite bank in the eastern portion. Within the City of Medicine Hat there are currently records from both sides (Powell and Russell 1992b; 1993a; ASRD 2004; FWMIS 2006).
Within the Saskatchewan range, habitat used in the West Block is described as similar to that of the juniper dune badlands in the Manyberries Hills of Alberta (Powell et al. 1998). In the East block, lizards were found to be occupying relatively unvegetated lower slopes of the coulees and ravines with some parts being covered thickly with grass (Powell et al. 1998).
Short-horned Lizards are moderately tolerant of human presence. In general, they are not so thoroughly upset by handling as to vacate their home ranges even when captured repeatedly (e.g. Powell 1982; James 1997). Small-scale disturbances, where the habitat is allowed to return to its former state, are likely only temporarily disruptive for these lizards.
Habitat trends
As the known distribution of Short-horned Lizards in Saskatchewan falls within the proposed borders of the Grasslands National Park, the remaining available habitat would seem secure for those particular populations. However, available habitat for Short-horned Lizards in Alberta should be considered to be declining, though not at the same rate in all areas. The habitat type favoured by Short-horned Lizards in Alberta has generally been less attractive to agricultural interests due to its steep and uneven topography, and its generally ‘unproductive’ nature. In addition, this entire region tends to be only sparsely populated with people. On the whole, these factors have probably ensured the maintenance of lizard populations thus far. Development and the accompanying disturbance can appear to be slow processes in these regions and may seem minimal to human observers that are not long-time occupants. However, it is worth considering that there are several areas of habitat, or potential habitat, which have either undergone extensive losses, or are currently experiencing a considerable amount of disruption.
The most significant cause of overall habitat loss in the Mixed-grass subregion is undoubtedly that area converted from native vegetation to cultivated agriculture. Fortunately, grazing is the predominant land use (55%) in the Dry Mixedgrass ecoregion of Alberta (NRC 2006). Additionally, approximately 35% is under dry-land cultivation, with another 10% or so committed to irrigation (NRC 2006). Losses to road construction, oil and gas development, and urban development have also contributed to reduction of native habitats.
Notable areas of habitat loss for the Greater Short-horned Lizard in Alberta include those along the extent of the Forty-Mile coulee, where the creation of dams for agriculture, in combination with the widespread cultivation and irrigation that surround the coulee, is thought to have effectively eliminated habitat for this species (Powell and Russell 1992b; James 2002). Habitat along the north banks of the South Saskatchewan River, and in the extreme south, along the Milk River and tributaries, appears generally intact, although the expansion of irrigation along the South Saskatchewan River is noticeable. It is puzzling, as noted earier, that so many locations along the Milk River yielded no captured lizards in recent surveys (James, 2002).
One significant area that continues to experience disruption is the Manyberries Hills region, where petrochemical interests, with the related roads, pipelines, and well-site development, have persistently expanded (Figure 5, 6). Applications for the surface mining of humate, used as a soil conditioner, and ammonite, a semi-precious stone derived from fossilized ammonites, for use in jewelry, have also been put forward for the Manyberries Hills (Geoff Smith, pers. comm.). Recently, a ‘Protective Notation’, which is a description added to the legal land locations of this crown-owned land, has been established within the Manyberries Hills Sensitive area (Geoff Smith, pers. comm.). This restricts any new industrial development from occurring, while permitting those with existing dispositions and access routes to continue operations.
Habitat protection/ownership
In Alberta, the ‘marginal’ land types that are preferred by Greater Short-horned Lizards are governed by a diverse set of owners and landlords. More than a dozen individual ranching companies, as well as least six individuals, the federal, provincial, and municipal governments, one community pasture run by a grazing association, and one Irrigation District have jurisdiction over the land for which there are records of Short-horned Lizards (J. James pers. records). The multitude of stakeholders significantly complicates the matter of observing these populations. Relationships with landowners and lease-holders is therefore of fundamental importance to maintaining dialogue regarding the species in Alberta.
Figure 5. A) Location of the Manyberries Sensitive Area (blue polygon) near Manyberries, Alberta. Short-horned Lizards have a high association with the Manyberries badlands features (stippled polygons), particularly with three specific vegetation types within (green shaded regions) (From Kissner 2005). B) Time series of all well locations (black dots) in the Manyberries Sensitive Area (border) and adjacent areas. The Manyberries Sensitive Area encompasses the Manyberries Hills sub-population of Short-horned Lizards. Underlying polygons indicate Greater Short-horned Lizard habitat (From Kissner 2005).
Figure 6. The number of new wells in the Manyberries Sensitive Area from 1940 to present.
The situation with regards to the land upon which Short-horned Lizards are found inSaskatchewanis in complete contrast with that in Alberta. In Saskatchewan, all records for Short-horned Lizards fall within the current Grasslands National Park proposed boundaries (Powell et al. 1998). Separate, and presumably isolated, populations are found in each of the two Blocks of this relatively new, and as yet incomplete, National Park. Powell et al. (1998) suggested that a lack of reliable records suggests it is unlikely the species occurs outside of the proposed park boundary in that province. Those lands that remain to be incorporated into Grasslands National Park are likely under private ownership of neighbouring ranches and, although not under guardianship of the federal government, are not likely to be at any greater risk.
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