ANGILLETTA, M.J.*; PRINGLE, R.M.: Thermal Requirements of Offspring Drive the Nesting Behavior of Fence Lizards

In squamate reptiles, thermal properties of nests have dramatic consequences for the survival and phenotypes of offspring. Optimal nest sites have been predicted from laboratory studies of the growth and survival of embryos, but tests of these predictions have been hampered by the inability to locate natural nests. We used radiotelemetry to observe the activity of 16 gravid fence lizards (Sceloporus undulatus) in the Pine Barrens of New Jersey. Females made large excursions from their home ranges to locate nesting sites in exposed substrates, but returned to their home ranges within 24 hours of nesting. Nest construction began after dark and was completed by morning. In part, the thermal requirements of offspring explain both the location of nests and the time of nesting. At all times of the day, temperatures at nest sites were significantly higher than temperatures at random sites, indicating that females preferred to construct nests that would provide a warmer but more variable thermal environment. Nests in exposed substrates permitted embryos to attain temperatures between 28-32 &deg C for approximately 8 hours per day, whereas nests at random sites would have been too cold to permit successful incubation. Operative temperatures at nest sites were too high to permit females to nest between 1000 and 1700 h. The nesting behavior of fence lizards corresponded well with predictions derived from laboratory studies of lizard embryos.