The origins and functions of bowers in the Bowerbirds: a review and synthesis

Bowerbirds (Aves: Ptilonorhynchidae) are unique among birds in that males build unusual structures called ‘bowers’ which function exclusively for sexual signalling. Research suggests that bowers are incorporated in male display performances in specific ways and may function to reduce threat levels associated with intense display behaviours and control the field of view of attending females. However, the evolutionary origin of bower-building behaviour in bowerbirds remains enigmatic. Here, we review the literature investigating bower function as well as the natural history of bowerbirds and discuss how bowers may have evolved. We suggest that the ancestral bowerbird may have first displayed using naturally occurring structures and that bowers initially evolved to enhance the efficacy of pre-existing sexual signalling behaviours by affording males greater control over the visual perspective of receivers. This represents a unique form of sensory niche construction, in which males create a specialised sensory microhabitat allowing them to control both the content and timing of what females can see and hear, thus shaping patterns of selection on male ornaments and display behaviours. The initial origins of bowers may, however, be attributable to an evolutionarily primitive behaviour in which males incorporate some form of naturally occurring structure in display.