Pregnancy affects flight behavior in big brown bats (Eptesicus fuscus)

Pregnancy involves increased body mass and decreased locomotor performance in many species and can be especially impactful on volant animals. To test the hypothesis that bats modify flight behavior to adjust for pregnancy-related increases in mass, we recorded thermal video from a maternity colony of big brown bats (Eptesicus fuscus) as they emerged from a roost, during periods associated with pregnancy and post-pregnancy. From video tracking, we calculated the vertical drop distance before upward motion (UM), time from emergence until UM, average speeds before and after UM, and average wingbeat rate per second (WBR). Bats recorded during the pregnancy period had a significantly larger drop distance, longer time until UM, faster flight speed before UM, and higher WBR compared to bats recorded during the non-pregnancy period. Our results suggest that pregnancy has a significant effect on flight in female bats, with a particularly strong impact on achieving UM after emergence. However, the higher WBR recorded from bats flying during the pregnancy period implies that bats acclimate to such changes in body mass by altering their flight behaviors to sustain UM while pregnant.