Montana Field Guide

EGGS:
The Greater Short-horned Lizard is viviparous, eggs develop internally, and females give birth to live young.

HATCHLINGS:
Broods can include up to 30 neonates or more, averaging about 12-18 (Smith 1941, Goldberg 1971, Ashton and Ashton 1998, Hammerson 1999), although broods are smaller in the north of their range (Powell and Russell 1991b, Hammerson 1999). Clutches range from 5 to 36 young (3 to 15 in the Pacific Northwest) during July to September (Nussbaum et al. 1983, Stebbins 2003). Newborn young are generally adult-like in appearance, with a broad and flattened body shape. They are about 2.0-2.5 cm (0.8-1.0 in) snout-vent length (SVL) and weigh about 0.7 – 0.8 g (0.02-0.03 oz), growing up to 3.8 cm (1.5 in) by the time of first hibernation (Goldberg 1971, Powell and Russell 1991b, Ashton and Ashton 1998).

JUVENILES AND ADULTS:
The body is broad and flattened. The back is spiny, especially noticeable in a single row of scales fringing each side of the body. Spines at the back of the head are stubby and about as long as they are wide at their base (Hammerson 1999, Stebbins 2003). A noticeably wide and deep notch separates the right and left horns at the back of the head (St. John 2002). The coloration of the back can be shades of gray, brown, or pink, usually blending cryptically with the soil, and can vary somewhat from region to region, as well as at single localities and even single broods (Ashton and Ashton 1998). There are typically two paired rows of dark brown blotches on the back that are often edged in white. Maximum total length (TL) is approximately 15 cm (5.9 in) (Hammerson 1999, St. John 2002, Stebbins 2003). In males there is a swelling at the base of the tail, and the tail is proportionally longer than in females. Females at 18 g (0.63 oz) outweigh males at 10 g (0.35 oz) and mature females are larger on average than males (7 cm (2.8 in) SVL versus 5 cm (2.0 in) SVL) (Powell and Russell 1985b, James et al. 1997).

The broad, flattened body separates this lizard from the other three lizard species regularly documented in Montana. The range overlaps only with the Common Sagebrush Lizard (Sceloporus graciosus). The Pigmy Short-horned Lizard (Phrynosoma douglasi) is present in adjacent southeastern Idaho and has been reported once from the Centennial Valley, Beaverhead County, in extreme southwestern Montana (Maxell et al. 2003). Adults of the Pigmy Short-horned Lizard are much smaller than the Greater Short-horned Lizard (Phrynosoma hernandesi), they lack the wide notch between the horns on the back of the head that gives the head of the Greater Short-horned Lizard a “heart-shape” appearance when viewed from above, and the small horns on the back of the head project almost vertically, rather than horizontally as in the Greater Short-horned Lizard (St. John 2002, Werner et al. 2004).

No information currently exists regarding the migration patterns of Greater Short-horned Lizards in Montana.

This species occurs in sagebrush and grassland habitats. Occasionally in the presence of sedimentary rock outcrops (limestone, sandstone) and glacial drift. As well in areas with open stands of Limber Pine (Pinus flexilis) and Utah Juniper (Juniperus osteosperma) or Ponderosa Pine (Pinus ponderosa) (Mosimann and Rabb 1952, Werner 1974, Dood 1980, Hendricks 1999a, Vitt et al. 2005).

Favored areas in Montana tend to have a relatively high percentage of open bare ground and loose, sun-baked soils. 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. Individuals were also present on flats of relatively pebbly or stony soil with sparse grass and sagebrush cover (Paul Hendricks, personal observation).

Elsewhere, the Greater Short-horned Lizard is an animal of short-grass and mixed-grass (Stipa and Bouteloua) prairies, sagebrush (Artemisia sp.) and other shrubland types, and open coniferous forest in mountains. They often occur in open, shrubby or wooded areas (e.g., Piñon-Juniper, Pine-Oak Woodlands) with sparse vegetation at ground level and easy access to sunlight. Soil substrate may vary from rocky to sandy, but loose soils are usually present (Hammerson 1999, Stebbins 2003). In Alberta and Saskatchewan, Greater Short-horned Lizard is often found in coulees and small canyons associated with streams and rivers in terrain of exposed “badland” shale, with a ground cover that includes Creeping Juniper (Juniperus horizontalis) (Powell and Russell 1991a, 1998, Powell et al. 1998). In Colorado, this species was encountered frequently in both Black-tailed (Cynomys ludovicianus) and White-tailed (C. leucurus) Prairie Dog colonies (Clark et al. 1982).

Adults and juveniles are “sit-and-wait” predators that hunt mainly by sight. Ants and beetles are the most frequent foods across the range, but several other orders of arthropods are also taken (Pianka and Parker 1975, Laird and Leech 1980, Montanucci 1981, Powell and Russell 1984, Hammerson 1999). The diet in Montana is virtually undescribed; stomach contents of three individuals from coulees near the Marias River, Toole County, included mostly ants with a few beetles, grasshoppers, and spiders (Mosimann and Rabb 1952).

Adult Greater 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 occurring 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 midday hours. 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 (Athene cunicularia) have been reported (Hammerson 1999). Additionally, birds have been identified as the primary predatory group (Russell and Bauer 1993). The annual period of activity in Montana is poorly defined, and no predators have been reported.

Home ranges of radio-tagged individuals in Alberta ranged from 4.4-2400 square meters (14.4-7,874 square feet) (James et al. 1997), with movements by females exceeding 100 m (328 ft) over a one-week period prior to mating, and as much as 266 m (873 ft) during the week prior to hibernation. Home ranges may be larger, because individuals are relatively sedentary but make irregular long movements that vary with the season (Powell and Russell 1998). The Greater Short-horned Lizard does not appear to be territorial (Powell and Russell 1998), although it exhibits some degree of site fidelity. A juvenile displaced 400 m (1,312 ft) returned to its capture site in less than a year and was subsequently captured twice more at this location (Pianka and Parker 1975). Little information is available on survival rate and longevity. Recapture data suggested high juvenile mortality in Alberta, whereas adult survival was considered relatively high (Powell and Russell 1991b, 1998). This pattern appears to be normal for other horned lizard species (Pianka and Parker 1975).

Based upon information gathered from other areas within the species' range, adults mate shortly after emerging from winter dormancy in late March to early June, depending on elevation and latitude. The Greater Short-horned Lizard is viviparous, giving live birth (Nussbaum et al. 1983, Stebbins 2003). Young are born about two or three months after eggs are fertilized, mostly during early July to early August in Arizona (Smith 1941, Goldberg 1971), and late July to early August in Colorado, southern Wyoming, and Alberta (Powell and Russell 1991b, Ashton and Ashton 1998, Hammerson 1999). Size of eight litters from Alberta ranged from 6-13 young (Laird and Leech 1980, Powell and Russell 1998). One litter from Wyoming included 13 young approximately 2.3 to 2.4 cm (0.9 in) SVL at birth and consisted of two color morphs and four stillborn (Ashton and Ashton 1998). Five litters in Colorado ranged from 14-18 young (Hammerson 1999), and 12 litters from Arizona included 9-30 young (Smith 1941, Goldberg 1971). Sexual maturity of females is attained by the age of two years in Colorado (their third calendar year) and around 5-6 cm (2.0-2.4 in) SVL (Nussbaum et al. 1983, Hammerson 1999). In Alberta, males apparently reach sexual maturity in the second year, following their first winter dormancy, although females appear to mature later (Powell and Russell 1985b, 1998). Sexual maturity is reached by two years of age in the southwestern states (Pianka and Parker 1975).

Little information is available from Montana on any aspect of the reproductive biology of this species. Ten captive adult females from near Warren, Carbon County, gave birth in the first week of August (J. Barron, personal communication), and young about 3.0-3.5 cm (1.2-1.4 in) SVL have been observed in this area in August and early September (Hendricks 1999a, P. Hendricks, personal observation).

The following was taken from the Status and Conservation section for the Greater Short-horned Lizard account in Maxell et al. 2009.

At the time the comprehensive summaries of amphibians and reptiles in Montana (Maxell et al. 2003, Werner et al. 2004) were published, there were about 130 total records for Greater Short-horned Lizard from 27 counties, with records generally widely scattered across the state east of the Continental Divide. Cope (1879) considered the Greater Short-horned Lizard about the most abundant reptile (second only to the Prairie Rattlesnake, (Crotalus viridis)) along the Missouri River, but it is no longer thought common anywhere in Montana, with the possible exception of some of the counties bordering Wyoming (Maxell et al. 2003). Populations in Carbon County appear to be robust (Vitt et al. 2005, J. Barron, personal communication), with many recent sightings (Barron reported 140 individuals near Warren in 2004) during favorable conditions. However, trend estimates remain unavailable for any locality in Montana, including areas of recent surveys. Connectivity of populations is unknown. Large gaps of a 100 km (62 mi) or more exist between some documented occurrences north of the Missouri River, and status is uncertain west of the Mussellshell River and south of the Missouri River. At the local scale, limited data suggest this species is relatively sedentary, with some degree of site fidelity, although females may move 100 m (328 ft) or more prior to mating or winter dormancy (Pianka and Parker 1975, James et al. 1997, Powell and Russell 1998). Thus, populations appear vulnerable to habitat fragmentation. Densities of this species have not been determined with any degree of accuracy but are thought to be generally low (considerably <50 individual/ha) (Pianka and Parker 1975, Powell and Russell 1985b), although perhaps locally fairly common (Hammerson 1999). Risk factors relevant to the viability of populations of this species are likely to include habitat loss/fragmentation, grazing, fire, road and trail development, on- and off-road vehicle use, use of pesticides and herbicides, oil and gas development, and surface mining. However, perhaps the greatest risk to maintaining viable populations of Greater Short-horned Lizard in Montana is the lack of baseline data on its distribution, status, habitat use, and basic biology (Maxell and Hokit 1999), which are needed to monitor trends and recognize dramatic declines when and where they occur. Few studies address or identify risk factors. In an Idaho study (Reynolds 1979), the closely related Pigmy Short-horned Lizard was four times more abundant in sagebrush habitat than in sites dominated by exotic Crested Wheatgrass (Agropyron cristatum), and more abundant in sagebrush habitat grazed by sheep than in ungrazed sagebrush and either grazed or ungrazed Crested Wheatgrass. A greater abundance of invertebrates may explain the preference for sagebrush over Crested Wheatgrass habitat (Reynolds 1979). More open ground for basking in grazed sagebrush may explain its preference over ungrazed sagebrush (Reynolds 1979, Hammerson 1999). Local extirpations of Greater Short-horned Lizard in Colorado have occurred in areas of intense cultivation and urban expansion, although this species seems to do well in areas used for livestock grazing (Hammerson 1999), perhaps because grazing reduces vegetative cover. Increased vehicular traffic in areas of oil and gas exploration and development have probably reduced populations in parts of Colorado (Hammerson 1999). Use of insecticides to control grasshopper infestations could also depress populations of this species, which feeds on these and other ground-dwelling insect species.