Basking in the moonlight? Effect of illumination on capture success of the endangered giant kangaroo rat

Abstract

Bright moonlight is thought to increase predation risk for nocturnal rodents and consequently reduce their activity levels and capture rates. We examined the effect of moonlight on the foraging activity and capture success of the federally endangered giant kangaroo rat (Dipodomys ingens) in the Carrizo Plain National Monument, California. D. ingens is adapted to open grasslands, a habitat type where moonlight should strongly influence its visibility to predators. Using a trapping data set of 11,353 captures from 2007 to 2009 and accounting for factors such as cloud cover, temperature, abundance of the San Joaquin kit fox (Vulpes macrotis mutica), plant biomass, trap acclimation, and trap effort, we found a consistently positive effect of moonlight on capture success. In foraging trials we detected no effect of moonlight on giving-up densities or time spent at seed piles. Our results suggest that giant kangaroo rats do not perceive a higher risk of predation in bright moonlight. Nocturnal rodents that rely on early visual detection of predators might benefit from moonlight as much as their predators do, thus resulting in no net change in predation risk.