The courtship displays of male broad-tailed hummingbirds consist of highly synchronized bursts of rapid movement, noises and visual signals that occur within 300 milliseconds (the blink of a human eye). The findings are reported in Nature Communications.
Male broad-tailed hummingbirds perform courtship displays to females by climbing vertically to about 30 metres and making sequential U-shaped dives. During these dives, males produce dive-specific mechanical noises with their tails and visual signals from their gorgets (a patch of colour on the throat). However, the degree to which the different components are synchronized during the display is unknown.
Benedict Hogan and Mary Caswell Stoddard created video and audio recordings of 48 dives performed by male broad-tailed hummingbirds in the wild. The authors then applied a multi-angle imaging technique to determine how a female would perceive the male’s iridescent gorget during the dive. They found that during dives, the sound and colour perceived change dramatically. They estimated that the female perceives a 6.5% shift upwards and 4% shift downwards in the frequency of the male’s sound as they approach and depart respectively, owing to the Doppler effect. This change is directly related to the speed and trajectory of the dive, they conclude. In addition, the geometry of the dive - combined with the high speed - suggests that the male’s gorget is only briefly visible to the female (approximately 120 milliseconds), and the perceived colour changes rapidly from red to black.
The authors argue that their findings highlight the importance of accounting for motion and orientation when investigating animal displays.