Montana Field Guide

The short-horned lizard body is broad and flattened. The back is spiny, with an especially noticeable single row of scales fringing each side of the body. The spines at the back of the head are about as long as wide at the base. The coloration of the back usually blends cryptically with the soil and can vary somewhat from region to region and at single localities. The maximum total length is about 15 centimeters. In males, there is a swelling at the base of the tail, and the tail is proportionally longer than in females. Newborn young have the broad and flattened body shape, and are about 2.0 to 2.5 centimeters snout-vent length and up to 3.8 centimeters by the time of first hibernation.

The broad, flattened body separates this lizard from the other three lizard species regularly documented in Montana, and the range overlaps only with the sagebrush lizard. The pigmy short-horned lizard has been reported from extreme southwestern Montana, in the Centennial Valley, Beaverhead County (Maxell et al. 2003), but adults of this species are much smaller than short-horned lizards, the small horns on the back of the head project almost vertically rather than horizontally, and they lack the wide notch between the horns on the back of the head that gives the head of short-horned lizards a "heart-shaped" appearance when viewed from above (St. John 2002).

No information currently exists regarding the migration patterns of short-horned lizards in Montana.

Habitat use in Montana is poorly described, but appears to be similar to other regions. Reports mention individuals on ridge crests between coulees, and in sparse, short grass and sagebrush with sun-baked soil (Mosimann and Rabb 1952, Dood 1980). On the southern exposures of the Pryor Mountains, Carbon County, individuals occur among limestone outcrops in canyon bottoms of sandy soil with an open canopy of limber pine-Utah juniper, and are also present on flats of relatively pebbly or stony soil with sparse grass and sagebrush cover (P. Hendricks personal observation).

This species is an invertivore. The diet of short-horned lizards includes especially ants and beetles, as well as other insects, spiders, snails, sowbugs, and other invertebrates. Individuals may sometimes gorge themselves on a single type of prey (Hammerson 1999). The diet in Montana is virtually undescribed; stomach contents of three individuals from coulees near the Marias River in Toole County included mostly ants with a few beetles, grasshoppers, and spiders (Mosimann and Rabb 1952).

Adult short-horned lizards are diurnal and active during the warmer daylight hours. Specific information for Montana is limited, but information from other areas within their range indicates they may appear as early as late March (Hammerson 1999), with most surface activity in the northern parts of the range occuring from mid-April to mid-September. Extreme records in Alberta extend from April 1 to November 10 (Powell and Russell 1998), but most have disappeared by the mean date of the first fall frost. Young-of-the-year are generally not active during mid-day hours, and small lizards appear more dependent on air temperatures than on substrate temperatures, while large ones are more dependent on substrate temperature. Predators of this species are mostly unknown, but striped whipsnake (Masticophis taeniatus) and Burrowing Owls (Speotyto cunicularia) have been reported (Hammerson 1999), and birds have been identified as the primary predatory group (Russell and Bauer 1993). The annual period of activity in Montana in poorly defined, and no predators have been reported.

No studies of the life history and reproduction of this species have been conducted in the state. In extreme southern Montana, young about 3.0 to 3.5 centimeters snout-vent length have been observed in early August and early September (Hendricks 1999, P. Hendricks personal observation).

Based upon information gathered from other areas within the species' range, adult short-horned lizards mate shortly after emerging from hibernation in late March to early June, depending on location, and young are born about two or three months after eggs are fertilized. The short-horned lizard is viviparous, giving live birth to 5 to 36 young (3 to 15 in the Pacific Northwest) during July to September (Nussbaum et al. 1983, Stebbins 1985). The size of 8 litters from Alberta, born in late July to early August, ranged from 6 to 13 young (Laird and Leech 1980, Powell and Russell 1998) and 5 litters in Colorado ranged from 14 to 18 young (Hammerson 1999). A litter of 13 young was born in southern Wyoming in early August (2.3 to 2.4 centimeters snout-vent length at birth) and consisted of two color morphs (Ashton and Ashton 1998); 4 young were stillborn. Sexual maturity is reached in at least two years (Nussbaum et al. 1983, Hammerson 1999).

Threats to this species in Montana are speculative, due to lack of study and poor survey coverage. The short-horned lizard was considered the most abundant reptile along the Missouri River in Montana in the late 19th Century (Cope 1879), second only to the western rattlesnake, but it is no longer thought common anywhere in the state, with the possible exception of southern Carbon County (Maxell et al. 2003). The relatively few records in recent years parallel the pattern for Colorado (Hammerson 1999), but inadequate survey coverage makes conclusions regarding trends in Montana tenuous. Habitat loss due to the conversion of prairie to cropland has undoubtedly contributed to the apparent decline, but livestock grazing is probably not a serious threat to any population, judging from reports in other regions. However, clearing of sagebrush to increase grass production for livestock could have detrimental impacts on local populations of short-horned lizards. Off-road recreational vehicle traffic and increased traffic associated with road building to oil and gas developments in eastern Montana could also have negative impacts on some populations. Indiscriminant use of insecticides to control some insect species could also affect the food supply of this lizard. No management activity for this species in Montana is currently underway, nor is any proposed at this time, but the conversion of native prairie to cropland or other use will contribute to the decline of this species in the state. Collecting of animals for export to the pet trade should be prohibited. Within the range of the short-horned lizard in Montana where sagebrush control is planned, some sage should be left in a network of patches to insure population persistence of these lizards. Given the small home range size of the species, thinning of sagebrush or removal in small patches is probably a better management guideline than removing sagebrush entirely or in large patches.