Mountain Short-horned Lazard. Phrynosoma hernandesi

Description: A moderately small lizard with a snout-vent length of 40-70 mm. Body flattened and ovoid in outline, with short limbs and tail. Head short and snout blunt. Small horn-like scales at the back of the head. A single row of fringed scales along the sides of the body between the front and hind limbs. Throat scales small. Back covered with rows of enlarged tubercles amongst smaller granules. Beige or grey above, blotched with dark brown and speckled with white. Generally cryptic against its background. A pair of dark brown blotches above the shoulders. Area under the throat and on the chest may be tinged with yellow or beige; otherwise the venter is white.

Variation: Females are considerably larger than males. Males and females grow at the same rate, but males cease growing earlier than females and thus become sexually mature at a smaller size and younger age. Males may mate in their second summer; females not until their third. Juveniles have the appearance of miniature adults.

Natural history: Diurnal. In Alberta, lives at the interface of short- grass prairie and coulee rims, chiefly on south-facing slopes. Population densities in Alberta appear to be lower than those in adjacent regions to the south. Forages among sagebrush, to which the species is primarily restricted. Basically a sit-and-wait predator. Eats insects, chiefly beetles and ants, some grasshoppers and any other small invertebrates it can procure. It is quite cold-tolerant and is active from early April to mid-October. It is live-bearing.

After mating, the females remain at the coulee rims while the males disperse into the short-grass prairie. Preyed upon primarily by birds. The horns may be a deterrent against potential snake and mammalian predators, but this is probably less effective than in other species with larger horns. Seeks shelter under sagebrush and other vegetation during the hottest part of the day. May also burrow to obtain shelter or use the burrows of small rodents. Complex shuttling behaviour is involved in temperature regulation throughout the day. Over the active season, individuals cover considerable distances, with the length of movements being greatest in the spring and fall. Shallow hibernacula are excavated in sheltered slopes. Insulation of snow cover may be significant in increasing survivor- ship through the winter, although winter mortality appears to be significant.

Reproduction: Mating takes place in spring, soon after emergence. The females give birth to live young, and up to ten individuals are born in late June or early July. Juveniles have a snout-vent length of about 20 mm at birth. While gravid, females exhibit restriction to a small home range.

Distribution: Limited to the extreme southeastern corner of the province, and is found only in arid, short-grass prairie regions. It occurs south from the South Saskatchewan River valley to the Montana border, and west from the Saskatchewan border to the region of Del Bonito. Extralimitally, it occurs from the Continental Divide eastwards to the Great Plains. To the south, it extends through Utah and eastern Nevada to Arizona, New Mexico and west Texas. Populations as far south as Durango, Mexico may also be referrable to this species although the biogeography of horned lizards is in need of revision as a result of recent systematic analyses. It is chiefly found in mountainous areas in the southern parts of its range.

Conservation status: The mountain short-horned lizard has been the subject of considerable investigation over the past two decades. These studies have revealed that population densities are low but that, except where disturbed by oil and gas exploration, it seems to be maintaining itself at a sustainable level.

Remarks: Alberta short-horned lizards were formerly assigned to the species Phrynosoma douglasi. However, molecular data have revealed that lizards previously considered to belong to several different subspecies of P. douglasi are more appropriately allocated to P. hernandesi.

Significant references: Chandler 1965; Clark and Chandler, 1992; Clark, G.W. and Bradford 1969; Fitch 1985; Guyer 1978; Guyer and Linder 1985; Heath 1964, 1965; James et al. 1997; Laird and Leach 1980; Lynn 1965; Medica et al. 1973; Milner 1979b; Montanucci 1983,1987,1989; Montanucci and Bauer 1982; Mosimann and Rabb 1952; Nero 1957; Pianka and Parker 1975; Powell 1982; Powell and Russell 1984, 1985a, b, 1991a, b, 1992, 1993, 1994, 1996b, c; 1998; Prieto and Whitford 1971; Reeve 1952; Schowalter 1979; Scott 1976; Sherbrooke 1981,1987; Sherbrooke and Montanucci 1988; Smith et al. 1999; Werschkul 1982; Williams 1946; Zamudio et al. 1997.