Temporal scale and conspecific density drive moonlight preferences of a nocturnal granivore

Abstract Foraging animals must balance energy gain with predation risk. In nocturnal animals, this tradeoff is often mediated by moonlight, which helps to find food but also increases exposure to predators. Although most studies suggest rodents avoid moonlight, prior research has largely focused on open habitats and used lunar phase as a crude proxy for illumination. We investigated how fine-scale moonlight brightness affects foraging in yellow-necked mice (Apodemus flavicollis) removing Quercus robur acorns in a broadleaf forest. Using complementary analyses, we examined foraging across nights and the timing of foraging bouts within nights. We expected that foraging would decrease with increasing moonlight, temporal preferences would be less pronounced under high mouse density, and sensitivity to moonlight would vary with residual reproductive value (influenced by sex and body mass) and behavioral type (exploration in open-field tests). Contrary to predictions, seed removal was higher during bright, clear nights. However, within nights, mice concentrated foraging efforts during darker intervals. This pattern is consistent with higher foraging efficiency on bright nights combined with avoidance of high-risk periods within those nights. As predicted, high mouse abundance reduced selectivity for optimal foraging conditions. While behavioral types had no effect, across-nights analyses demonstrated that males and lighter individuals preferred darker nights, while within nights, females showed greater sensitivity to cloud cover, foraging under lower moonlight when skies were clear. Overall, these results indicate that moonlight preferences can vary with the temporal scale of analyses and individual traits, while preference strength declines with increasing conspecific density.