Effects of Simulated Moonlight on Activity in the Desert Nightsnake (Hypsiglena chlorophaea)

The desert nightsnake (Hypsiglena chlorophaea) is a small (< 60 cm snout-vent length), cryptic species of snake often associated with desert habitats of the intermountain western United States. This species is both an active and ambush foraging that feeds largely upon small snakes and lizards. For some nocturnal species, such as H. chlorophaea lower activity levels in response to a full moon may affect foraging time, as well as reduce the risk of predation. I collected snakes from May to August 2009 in central Washington State, and maintained in captivity using standard husbandry practices. Using moonlight levels gathered at the collection site, I compared the mean numbers of snake movements of 20 adult H. chlorophaea during three moonlight trials: new moon (0.05 lux), half moon (0.32 lux), and full moon (2.10 lux). For the 23 hr trial period, simulated moon-up during the half moon and full trials was from 2300 to 0300 hr. Based upon current field data on this species, I predicted that snakes would reduce activity in response to a full moon. During moon-up, there was no difference in the mean number of movements of snakes between the new or half moon trials. However, all snakes made fewer movements during the full moon trial.