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The distribution of the Plateau Fence Lizard (S. tristichus) reaches from Wyoming south through the plains and foothills of Utah and Colorado into New Mexico and Arizona. The Red-lipped Lizard (erythrocheilus) and the Northern Plateau Lizard (elongatus) were once considered separate subspecies; recent taxonomic restructuring reduced them to one species without distinction. In this guide they retain their individuality.
In Wyoming the Red-lipped Plateau Lizard is restricted to a narrow corridor along the Front Range of the Laramie Mountains at elevations between 6,000 and 7,200 feet, reaching from the Colorado border north to near Douglas. It inhabits the rocky outcrops, large boulders, and cliff habitats of hogback ridges of the shrubland and Ponderosa Pine communities within the foothill and montane life zones. Some of its range lies adjacent to but does not overlap with the Prairie Lizard, a type of distribution known as parapatric overlap.
They are diurnal insectivores and are active from late April through September. Males and juveniles usually emerge from hibernacula before females. These lizards typically lie-in-wait on a favorite perch and ambush prey such as ants, flies, moths, grasshoppers, and beetles.
They are medium to large lizards with snout-vent lengths just under 3 inches. The scales of the back and legs are overlapping, ridged (keeled), and lance shaped; those of the belly are smooth, non-overlapping, and diamond or polygon shaped. The dorsal background is light brown with two dorsolateral rows of 8-9 black zigzags or crimped markings which are bordered with light gray margins. The ventral background is white.
Males have a pair of elongated, vivid blue patches along the belly between the front and rear legs. In females, these patches are somewhat faded and have a greenish tint. Both sexes (though more intensely so in males) have a pair of black-bordered, blue throat patches that touch or merge together at the midline. The lips and snout of both sexes in breeding condition (once again, more intensely so in males) are reddish-orangeógiving rise to its surname. Gravid females may also display areas of yellow or pale orange along the tail. Males with larger and more saturated orange or red coloration show dominance over males with smaller or yellowish markings.
Breeding males are more prone to behavioral displays employing push-ups rather than head bobbing when defending territorial boundaries against other males and when attempting to entice females during courtship. They must take their time during courtship because females do not respond favorably to unsolicited advances. A femaleís rejection may include: lowering the head, arching the back, and walking with a sideways or lateral movement. Females lay a clutch of 8-12 eggs in May or June and often a second, smaller clutch is laid in July. Hatchlings begin to appear in August and September. Sexual maturity is reached in the 2nd or 3rd year.