Evolutionary Convergence in Foraging Niche and Flight Morphology in Insectivorous Aerial-Hawking Birds and Bats

Abstract

Some insectivorous birds and most insectivorous bats catch their prey in flight. This puts large demands on flight manoeuvrability and agility and calls for specialized adaptations in wing design. Aerial foraging is facilitated by low body mass and low wing loading, permitting high manoeuvrability and slow flight. Birds and bats with similar ecological foraging models (aerial-foraging in open spaces or among vegetation) show strong convergence in wing shape. Birds foraging in open areas (swifts, swallows) show similarities with open-field foraging bats, whereas birds hunting among or close to vegetation (flycatchers, Nightjar) are more like bats hawking near or within vegetation. The specific flight costs are lower (because of higher wing aspect ratios) in all the bats and in those birds that hawk insects in open areas than in birds that hawk among vegetation or that do not hawk insects in the air at all. The latter group is rather different from aerial-hawking birds and bats in wing design.