Pygmy short-horned lizard COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

The habitat requirements of the Pygmy Short-horned Lizard are poorly understood; however, it appears that a broad range of habitats is used. Generally, the species occurs in a variety of shrub-steppe and open forested ecosystems, but always on well-drained sites (Brown et al. 1995). Vegetation must be adequately sparse to permit heliothermy (basking) and to allow unencumbered movement through the understory (Sherbrooke 2003, Lahti 2005). However, vegetation is selectively used for shade when it is very hot (e.g., James 2004, Lahti 2005). Friable soils suitable for burrowing are needed somewhere within an individual’s home range, although the area can be dominated by very shallow or coarse-textured soils. In fact, lithosols (soils with significant rubble) were preferred in Kittitas County, especially by males in the spring (Lahti 2005). This habitat is similar in structure to habitat supporting high concentrations of Pygmy Short-horned Lizards in the Methow Valley of Okanogan County, between elevations of 750 and 1050 m asl (S. Fitkin pers. comm.). Contrastingly, in the Columbia Basin the lizards also are commonly seen in big sagebrush (Artemesia tridentata) stands with flat, deep aeolian soils (R. Friesz pers. comm.). However it appears that mostly adult females use these areas, having broader habitat tolerances than neonates or adult males (Lahti 2005). Some populations in Washington State occupy areas with sparse to moderate densities of antelope bitterbrush (Purshia tridentata), some big sagebrush, bitterroot (Lewisia rediviva), and snow buckwheat (Erigonium niveum) (S. Fitkin pers. comm.). Pygmy Short-horned Lizards are extremely cold tolerant and in the Oregon Cascade Mountains can be found up to at least 1,677 m asl (Brown et al. 1995) and occasionally over 2000 m asl in open stands of subalpine fir (S. Fitkin pers. comm.).

The only hibernaculum described for this species was in Kittitas County where a female repeatedly burrowed during cool nights and then was last observed in mid-October at a depth of 4 cm under uprooted sod (Lahti 2005). In southern Alberta, at latitude similar as the Okanagan Valley, Greater Short-horned Lizard hibernated on warm aspect slopes where soils are sufficiently friable to permit burrowing to a depth of 10 cm (James 2004).

Habitat trends

Approximately half of the native grasslands in the South Okanagan have been converted into intensively developed lands since 1940 (Bezener et al. 2006). This trend has accelerated in recent years with tremendous pressures from agricultural and residential development. The distribution of potentially suitable habitats in the Okanagan currently is highly fragmented. The remaining suitable habitat in the Similkameen is more contiguous but the soils are typically less friable.

A recent population projection for humans in the Regional District of Okanagan-Similkameen anticipates a total population increase of 30% between 2004 and 2031, adding 24,506 residents to the existing population of 80,822 (Hobson and Associates 2006). This development will lead to increasing density of existing urban and rural areas as well as the expansion of new neighbourhoods into outlying areas. The latter will have the greatest detriment on potential Pygmy Short-horned Lizard habitat.

Habitat in the remainder of the lizard’s range has also been significantly reduced from historic levels as a result of agricultural and residential development. The interior Columbia and Klamath basins retain 70% of their shrub-steppe and a mere 30% of their grassland ecosystems (Quigley et al. 1996).

Habitat protection/ownership

Land tenure was overlaid to determine land status of potential lizard habitat identified in the habitat use model. The majority of potential habitats occur on Indian reserves (31%) governed by three distinct Bands. Private lands (29%) account for the second greatest tenure of usable habitats. Most of this habitat is situated on a relatively small number of large ranches. The provincial government’s protected areas represent 18% of the usable habitats. Usable habitat on other conservation lands, such as private organizations (3%) and federal lands (5%) bring the amount of protected lands to 26%. The provincial government also has 14% of the usable habitat in an unprotected status and some of these lands (2400+ ha) are available for disposition (BC Government 2004). A national park reserve is being considered for the south Okanagan and lower Similkameen valleys that could include some existing protected areas with the possibility of some adjacent lands (T. Hurd pers. comm.). Table 1 summarizes ownership of potentially suitable habitats for the Short-horned Lizard in Canada.

Table 1. Tenure and Areas of Suitable Habitats for Pygmy Short-horned Lizards in Canada.
Tenure Area (ha) %
Fed. Crown - CWS
470
1%
Fed. Crown - NRC
1745
4%
Indian Reserves
12,919
31%
Prov. Crown - Protected
7234
18%
Prov. Crown
5910
14%
Private
11,859
29%
Private Conservation
1120
3%
Total
41,256
100%

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