Stereotypy of group flight in Brazilian free-tailed bats

Many bats form colonies and undergo nightly emergence in dense, fast-moving streams. Although the flight mechanics of individual bats have been well studied, the effect of flying in a group has not been studied with large aggregations under natural conditions. We tested the hypothesis that group size affects flight mechanics and behaviour in Brazilian free-tailed bats, Tadarida brasiliensis. We measured the flight path, flight path time and wing beat rate of individual bats by analysing videos of bats in flight and compared values across different flight group sizes. Flight path, flight speed and wing beat rate of individual bats were all unaffected by group size. Additionally, bats maintained a constant wing beat rate regardless of flight speed. These results suggest that Brazilian free-tailed bats experience neither an aerodynamic benefit nor a cost to travelling in groups.