Sonoran Collared Lizard (Crotaphytus nebrius)

Sonoran Collared Lizard, Pima Co., AZ. Photo by Jim Rorabaugh

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Description

The Sonoran Collared Lizard (Crotaphytus nebrius) is one of our more sizable lizard species (< 112 mm SVL) with a large head, a long slender tail that is round in cross-section, and long, powerful limbs. Tail length is usually about 1.9-2.1 times the SVL. The hind limbs, from groin to the tips of the toes, are about the same length as the SVL. The neck is distinctly narrowed and a gular fold is present. The dorsal scales are granular; the ventral scales are somewhat larger. The inside of the throat is black. Males grow to a larger size and their heads are broader and more heavily muscled than the females. Maximum female SVL is 98 mm (McGuire 1996). Also, males have enlarged postanal scales.

Both sexes have median dorsal pale spots that are larger than the size of the adjacent lateral spots. Distinct dark patches mark the groin and adjacent portions of the underside of the hind limbs in adult males. There are often dark patches just behind the front limb insertion points, as well. About four dusky crossbands are usually visible on the dorsum, separated by thin yellowish-tan interbands. Banding may extend onto the tail, but is typically faint. An inconspicuous pale, mid-dorsal stripe may be present on the tail. Banding on the body and tail is often obscured by numerous whitish spots. Two dark collars are present on the neck, the anterior of which most completely encircles the throat in adult males but often is broken mid-dorsally. The posterior collar is often broken along the mid-dorsal line and terminates at the shoulder (incomplete ventrally). This species generally lacks green or blue in the dorsal pattern, although some adult males show a hint of grayish-blue in the center of the back. The throat of adult males is marked by white dots over a ground color of pale gray laterally to darker gray or bluish-gray centrally. In Sonora and western populations, adult males may show a considerable yellow wash to the head, limbs, and/or sides of the body. The adult females are usually browner overall with more diffuse markings, although they develop post-breeding salmon-orange markings on the neck and sides of the body. The juveniles resemble adult females (including the salmon-orange markings), but are more strongly banded and reticulated. Size at hatching is 42-44 mm SVL.

The only other collared lizard found within the 100-Mile Circle is the Eastern Collared Lizard (Crotaphytus collaris). Its distribution lies generally to the east and north of that of the Sonoran Collared Lizard. The ranges of the two species are in close proximity in the Tucson area, where the Eastern Collared Lizard occurs in the Rincon, Santa Catalina, Tortolita, and Santa Rita mountains, and the Sonoran Collared Lizard occurs in the Waterman, Silverbell, and Tucson mountains, and at Black Mountain to the south of Tucson. The Sonoran Collared Lizard generally occurs to lower elevations, as well (probably to about 400 m in the Circle), whereas the lowest elevations for the Eastern Collared Lizard in the Circle are about 840 m. In the Circle, the Sonoran Collared Lizard is also almost exclusively an inhabitant of Sonoran desertscrub, whereas the Eastern Collared Lizard occurs in a variety of vegetation communities. McGuire (1996) discusses in detail areas in which the Sonoran Collared Lizard comes in close contact with the Eastern Collared Lizard and the Great Basin Collared Lizard (C. bicinctores).

The Eastern and Sonoran Collared Lizards are also generally diagnosable based on adult male colors and patterns. In the Eastern Collared Lizard the anterior dark collar is always incomplete ventrally through the gular region. Furthermore, adult male Eastern Collared Lizards vary considerably in dorsal coloration and may be green, turquoise, olive, brown, tan or yellow overlain with spots and faint banding.

Taxonomically, the Sonoran Collared Lizard was included within the Eastern Collared Lizard (Crotaphytus collaris) until recently. Axtell and Montanucci (1997) recognized it as a separate subspecies (C. c. nebrius), which was subsequently elevated to species by McGuire (1996). However, more recent genetic work found that the Sonoran Collared Lizard is polyphyletic and partially imbedded within the Eastern Collared Lizard. These findings may be explained by incomplete lineage sorting and recent introgressive hybridization, but the Sonoran Collared Lizard may not be a valid species (McGuire et al. 2007).

In the 100-Mile Circle, the Sonoran Collared Lizard is an inhabitant of Sonoran Desert mountain ranges, including relictual mountain-top semi-desert grasslands. However, to the south of our area, it also occurs in foothills thornscrub and marginally into oak savanna and tropical deciduous forest. Its distribution is limited to Arizona and Sonora. In Arizona it occurs south of the Gila River from the Gila and Tinajas Altas Mountains, Yuma County, east to near Tucson, and north to the Sierra Estrella, Buckeye Hills, and Maricopa Mountains. It has not been documented in the Baboquivari Mountains or points east of that range in the borderlands of Arizona. The Sonoran Collared Lizard is the only Crotaphytus west of Tucson and south of the Gila River, except for a population of the Great Basin Collared Lizard on the Sentinel Plain, Maricopa County (outside of the 100-Mile Circle). McGuire (1996) also reported a single specimen of the Great Basin Collared Lizard from Black Gap on the western periphery of the Sauceda Mountains, Maricopa County (also outside the Circle), but subsequent searches have failed to yield additional Crotaphytus from that area. Elevational range in the Circle is probably about 400-1426 m, with both high and low elevations in the Sierra Estrella. It occurs to at least 1189 m in the Ajo Mountains (T. Tibbitts, pers. comm. 2015). In Sonora, its distribution extends from the Sierra Tinajas Altas south and east to near Bacadéhuachi and Nacori Chico, and south to near Nuri and just south of Guaymas.

The natural history of the Sonoran Collared Lizard is poorly known, compared to for instance, the Eastern Collared Lizard. But it is a diurnal species often found basking on boulders in desert mountain ranges.  It is never found far from rocky slopes or boulder piles, and is quick to take refuge under rocks and in crevices if threatened. However, if captured or cornered, it will not hesitate to stand its ground, opening its mouth and biting its attacker if the opportunity arises. With a slow, careful approach, an observer may be able to get quite close to these lizards. But they are quite fast, and employ the tail for balance in bipedal locomotion. The tail does not detach easily, and if lost, does not regenerate (Babb 2009). While in rock crevices or other refuges, the tail is usually coiled so it is not vulnerable to predators. The adult males are highly territorial. The Sonoran Collared Lizard has been collected as early as 6 March and as late as 21 October in the 100-Mile Circle. Adults likely cease activity in September (McGuire 1996).

Breeding behavior and timing is not well studied, however, Babb (2009) says that breeding occurs in May and June and possibly up to 12 eggs are laid in June or July, which hatch in July through September. McGuire (1996) observed mating on 14 June in the Gila Mountains, Yuma County, and recently hatched lizards on 11 August and 19 September in southwestern Arizona. The diet of this species has not been investigated, but Collared Lizards in general feed upon a wide variety of invertebrates, such as grasshoppers, beetles, spiders, butterflies, moths, centipedes, and snails. Small lizards (e.g. Tiger Whiptails, Common Side-blotched Lizards) are also occasionally taken (see review in Fitch 1956).   In outdoor exclosures, Ornate Tree Lizards (Urosaurus ornatus) showed elevated corticosterone levels, responded more quickly, and hid for longer periods in the presence of Sonoran Collared Lizards than control animals not exposed to this predator (Thaker 2009).

The Sonoran Collared Lizard is listed as a species of least concern on the 2014 IUCN Red List. With a valid Arizona hunting license, four can be collected per year or held in possession, alive or dead. However, collection is prohibited in protected areas, such as Organ Pipe Cactus National Monument without special authorization. There is no reason to believe populations of this species are imperiled or in decline.

Suggested Reading:

Axtell, R.W. and Montanucci, R.R. 1977. Crotaphytus collaris from the eastern Sonoran Desert: description of a previously unrecognized geographic race. Nat. Hist. Misc. Chicago Acad. Sci. No. 201: 1-8.

Babb, R.D. 2009. Sonoran Collard Lizard Crotaphytus nebrius Axtell and Montanucci, 1977. Pages 108-111 in Jones, L.L.C., and R.E. Lovich (eds.), Lizards of the American Southwest: A Photographic Field Guide.  Rio Nuevo Publishers, Tucson, Arizona.

Brennan, T.C., and A.T. Holycross. 2006. Amphibians and Reptiles in Arizona. Arizona Game and Fish Department, Phoenix, AZ. 

Fitch, H.S. 1956. An ecological study of the Collared Lizard (Crotaphytus collaris). University of Kansas Publications, Museum of Natural History 8(3):213-274.

McGuire, J. A. 1996. Phylogenetic systematics of Crotaphytid lizards (Reptilia: Iguania: Crotaphytidae). Bulletin of Carnegie Museum of Natural History 32:1-142.

McGuire, J.A., C.W. Linkem, M.S. Koo, D.W. Hutchison, A.K. Lappin, D.I. Orange, J. Lemos-Espinal, B.R. Riddle, and J.R. Jaeger. 2007. Mitochondrial introgression and incomplete lineage sorting through space and time: phyllogenetics of Crotaphytid lizards. Evolution 61-12: 2879–2897.

Thaker, M. 2009. Hormonal mediation of alternative strategies: Integrating variation in antipredator responses, polymorphism, and learning. PhD dissertation. Indiana State University, Terre Haute.

Wells, W. 1997. Collared lizards of the genus Crotaphytus. Reptiles Magazine 5(4):48-75.

Author: Jim Rorabaugh

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