Habitat structure drives the evolution of aerial displays in birds

Abstract

Physical properties of the environment may shape signalling traits by determining how effective the signals are in affecting the behaviour of other individuals. Evidence abounds of signalling environment driving the evolution of colours and sounds, but little is known about its influence upon gestural displays. Here, we performed a continent-wide phylogenetic comparative analysis to test the hypothesis that habitat structure drives the evolution of aerial sexual displays in passerine birds. We found that aerial displays are seven times more likely to evolve in open habitats than in forests, likely as a result of physical properties that allow aerial displays to transmit more broadly in open habitats. Our results provide an emblematic example of how environmental factors may help predict the direction of evolution of otherwise unpredictable sexual traits. The broader range of aerial displays in open habitats may also mean that females can sample more males, potentially leading to more intense sexual selection over open-habitat, aerial-displaying males.