DIEL PATTERNS OF ACTIVITY AND OF SELECTED AMBIENT TEMPERATURE OF THE SAND-SWIMMING LIZARD SPHENOPS SEPSOIDES (REPTILIA: SCINCIDAE)

ABSTRACT

Diel patterns of activity and temperature selection were determined for two age classes of the sand-swimming skink, Sphenops sepsoides, under laboratory conditions. Activity levels were the highest between 1500 and 2100 h, and lowest between 2100 and 0600 h. Selected ambient temperatures averaged 29.7°C but varied during the diel cycle with the highest temperatures recorded at 1800 h and the lowest at 1200 h. Selected ambient temperatures were consistently about 1°C higher for juvenile than for adult individuals. The period that lizards were most active in corresponded to the period of highest selected ambient temperature. These patterns do not match those of nocturnal geckos in the field, which are the most active after dark but select high body temperatures during the day. However, these results are consistent with observations of activity and selected body temperatures of Eremiascincus fasciolatus, another sand-swimming skink. Field observations on S. sepsoides suggest that sub-surface activity is not initiated until after dark. The discrepancy between field and laboratory observations may be a consequence of vertical thermoregulation movements in the field that allow lizards to increase their body temperatures late in the day. These movements would not be reflected by trails or tracks on the sand surface in the field but would be reflected by trails or tracks on the sand surface in the laboratory where shallow sand levels allowed lizards to move only horizontally on the thermal gradient.