Pygmy short-horned lizard COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

Search effort

Pygmy Short-horned Lizards are very difficult to detect, as they can be either underground, or motionless and camouflaged. Therefore, negative search results do not confirm the absence of the species in an area. Four separate survey attempts have been made to find the Pygmy Short-horned Lizard in Canada. Stan Orchard conducted the first of these in 1989 (Orchard 1990). Surveys were conducted on the east side of Osoyoos Lake, Veronica Lake on Anarchist Mountain and Chopaka in the Similkameen. No lizards were observed but it is unclear how much effort was expended. 

A 10-day survey was conducted by G. Powell who searched the east side of Osoyoos Lake as far south as the International Border (Powell and Russell 1991b). If one assumes that approximately 100 hours were expended and that density might be similar to that reported for P. hernandesi at a study site in Saskatchewan (Powell and Russell 1998), then as many as four Pygmy short-horned Lizards could have been expected to be found. However, no lizards were found in their search. Search efforts in Washington State yielded less than one (0.71) individual per search hour (Lahti 2005) and up to three per search hour (S. Fitkinpers. comm.).

In 2003, the author conducted four surveys averaging four hours each for a total of 16 hours over a 20-ha parcel that was about to be developed into a vineyard (Sarell unpubl. data). No lizards were found despite very suitable habitat conditions. 

In 2004, a series of drift fences (totaling 200 m) and pitfall traps were installed for a week on the Osoyoos Indian Reserve (Reballato 2004). The site was dominated by big sagebrush, had silty soils and an abundance of harvester ants. Traps were checked daily but no lizards were captured.

Abundance

P. douglasii is considered to be fairly stable throughout most of its range (G5) with an assumed metapopulation of more than 10,000 individuals, but is considered vulnerable (S3) in Washington State (NatureServe Explorer 2005). There have only been two confirmed observations in British Columbia and although unconfirmed observations have been made as recently as 2004, the population is assumed to have dwindled or become extirpated. The majority of the population decline may have occurred prior to the 1900s. The greatest reported density of Pygmy Short-horned Lizards is 14 per ha in Idaho (Guyer and Linder 1985) but most sites are probably similar to that reported in Kittitas County, where 1.7 P. douglasii per hectare were found.

The abundance of Pygmy Short-horned Lizards in Canada, either historically or currently, is entirely unknown. Four surveys within the past 20 years have not revealed any individuals, but there appears to be a much larger area of potentially suitable habitat than has been surveyed and anecdotal reports continue to occur. 

The first record of the Pygmy short-horned Lizard in Canada was made by Charles de Bois Greene at Osoyoos in 1898 (Fannin 1898). He captured two individuals and these specimens are housed in the Royal BC Museum. It was previously speculated that the lizards were found on the east side of the valley, likely on the Osoyoos Indian Reserve (Orchard 1990, Powell and Russell 1991b). However, de Bois Greene lived on the west side of the valley and could have easily found them on the slopes above his house, which were undeveloped at the time (W. Prestonpers. comm.). There is some confusion regarding the collection date as Cowan (1936) cites the year as 1910 and that has appeared in other accounts (e.g., Gregory and Campbell 1984). Other early accounts cite the Pygmy Short-horned Lizard as occurring near Keremeos in the Similkameen Valley (Anderson 1901) or as far north as Vaseux Lake in the Okanagan Valley (Parham 1937). Neither of these accounts provides any substantiation to its claims. One individual was captured and released near Osoyoos by J.D. Gregson and G.P. Holland in 1937 (Orchard 1990). Apparently they provided a very compelling account. Bill Preston found another individual dead on the road near the Chopaka Border in the lower Similkameen Valley in 1960. Unfortunately the specimen was not collected. Vic Palermo found four during the 1970s, one each at Chopaka and Anarchist Mountain (East of Osoyoos), and two near Vaseux Lake. Palermo also recalled that the “old fellow on Highway 3 that sold turtles” reported seeing one near Kaleden (south of Penticton), probably in the 1970s. A poll conducted with Osoyoos Indian Band members (Chapman 1995) produced five accounts of six individuals, mostly observed in the 1970s and 1980s. More recently, reports have come from the Richter Pass, Cawston, and the Nk’Mip Desert and Heritage Centre east of Osoyoos. All but one observation were from sites in arid ecosystems. In total, 19 individuals have been reported (Sarell unpubl. data). This probably represents considerably fewer sightings than have been made of the Ogopogo in the same time period, but at least there are two lizards in a jar to provide an indisputable argument that they are not myth in British Columbia. However, until a confirmed observation is made, this lizard must still be considered extirpated from Canada.

Fluctuations and trends

Horned lizard populations are declining throughout most of their ranges due to anthropogenic impacts (e.g., Pianka and Vitt 2003). Fluctuations in horned lizard occurrence in specific areas have been observed and thought to be due to weather variation between years (Flat-tailed Horned Lizard Interagency Coordinating Committee 2003).

Rescue effect

Although undeveloped lands, which appear to be suitable Pygmy Short-horned Lizard habitat, occur immediately south of the International Border, the closest confirmed existing populations are 60 km further south. If this population is truly the nearest then recolonization through immigration appears unlikely given the small size and limited mobility of individual Pygmy Short-horned Lizards.

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