Diet and Estimated Energy Assimilation of Three Colorado Lizards

Ants and beetles were the primary foods of 60 eastern fence lizards and 25 desert spiny lizards during spring and summer in southwestern Colorado. Lepidopterous larvae and grasshoppers com- prised most of the food of 49 western whiptails. Although there was some seasonal change in the diet of all species, there was little qualita- tive difference in diet between sexes or age groups. Sand grains and small pebbles found in stomachs may act as abrasives which macerate hard exoskeletons. Female fence and desert spiny lizards had more food in their stomachs during the spring months than did males, probably to meet the metabolic requirements of egg-laying. Assuming that these species fill the stomach twice daily, that stomach capacity is twice that of the mean weight of the stomach contents, an assimilation efficiency of 2/3, and an energy value of 5363 calVg, the energy assimilated by an adult eastern fence lizard (15 g), western whiptail (22 g), and desert spiny lizard (30 g) is estimated as 0.83, 1.57, and 2.17 kcal/day (55, 71, and 72 cal/g/day), respectively.