Nesting and Hatchling Behavior of the Texas Horned Lizard (Phrynosoma Cornutum) (Report‪)‬

In 2006, we observed construction of nest chambers by two adult females and emergence of hatchling Texas horned lizards (Phrynosoma cornutum) at a 0.1-ha fragment of native short-grass prairie in Randall County, Texas. At 1835 h CDT on 25 May 2006, a female (80 mm in snout-vent length) was digging in hard, caliche soil. By 1900 h, she was underground and only partly visible in the excavated tunnel, which angled downward into the slope in an easterly direction with the opening facing west. Inside, the female was perpendicular to the entrance. While she worked in the nest chamber, her right hind leg and tail occasionally were visible. At times, she left the nest chamber to move the growing mound of soil away from the entrance. She was observed until darkness at 2110 h. On 26 May at 0700 h, she was resting at the open entrance to the nest chamber. By 0826 h, she had backfilled the nest chamber with soil, but location of the excavation remained identifiable and distinguishable from its surroundings. By 1200 h, the entrance to the nest chamber was undetectable. On 27 June 2006 at 1109 h, a second female (85 mm in snout-vent length) was digging a nest in dry, caliche soil ca. 0.3 m downslope and westward from a concrete slab. This nest-site was 9 m northeast of the first. The excavated tunnel angled slightly downward in a north-northeasterly direction with the opening facing south. By 1300 h, the female was inside the tunnel; however, unlike the first female, our attempts to observe her caused her to halt activities. Although we continued watching from a blind, she periodically halted activities to circle the entrance, look around, and occasionally move away from the nest. At ca. 2100 h, she began backfilling the nest chamber, using all limbs in concert to transfer soil from the mound into the tunnel and nest chamber. First, facing away from the entrance, she pulled soil with alternate right and left forelimbs toward the entrance and to within reach of her hind limbs. Her hind limbs then conveyed the soil in the same direction toward the entrance. She then turned 180[degrees] to face the entrance, scanned her surroundings, and proceeded transferring soil in the direction of the entrance with motions in reverse of the previous sequence. She first alternately used her extended hind limbs to bring soil to within reach of her forelimbs in the direction of the entrance. Her forelimbs continued to move soil forward toward the entrance. She then used her head to sort soil for placement as fill in the nest chamber. Motion of the head included a vigorous, mostly side-to-side, motion combined with a twisting motion. With this motion, she immersed her head into the loose, excavated soil now at the entrance. Hind limbs were extended outwardly, perpendicular to her body, as a brace to stabilize her body and, in combination with her left forelimb, provided a tripod to support her body. At the same time, her right forelimb repeatedly pulled soil from behind (from both beside and beneath her) in a forward direction so as to feed a continuous supply of soil to her head. The ensuing action of her head seemed to simultaneously lift and sift the soil, so that sifted particles were transported into the nest chamber. We propose that this action was to adequately fill space between eggs and layers of eggs to prevent collapse of the nest if rain events occurred during incubation.