Sociality and insect abundance affect duration of nocturnal activity of male parti-colored bats

Abstract

Patterns of activity in all animal taxa are selected to optimize time and energy spent foraging under varying conditions of food availability and predation risk. Social behaviors may play an important role in shaping these patterns. For example, animals can increase foraging efficiency via information transfer or reduce energy budgets by roosting in groups. Sociality in male temperate zone bats is rare and remains poorly understood. We determined the factors that influence duration of activity of male parti-colored bats (Vespertilio murinus), which go through a colonial and a noncolonial phase during summer. We radiotracked 14 bats, monitoring their activity for 37 nights, and correlated activity with weather conditions, lunar phase, and especially prey abundance and social status. We found no significant influence of environmental conditions (ambient temperature, wind speed, rain, and lunar phase) on the activity patterns of parti-colored bats. However, males were active longer, i.e., they invested more energy into foraging, when insect abundance was higher and when they were not living in colonies. Nights with higher prey availability provide bats with the possibility of higher caloric intake to balance the cost of flight, while increased efficiency of foraging with roost mates may allow for shorter foraging periods. Confirming a role of social context for the activity of males helps identify behavioral patterns without the confounding effect of added energy expenditure due to breeding, as is the case for females.