Most research on the courtship displays and behavior of songbirds has focused on polygynous male birds that woo multiple female mates. A new study finds, however, that in blue-capped cordon-bleus, Uraeginthus cyanocephalus, a socially monogamous African finch, both males and females make elaborate displays, especially when an audience is present.
Blue-capped cordon-bleus’ courtship displays include not just songs but also vibrations produced by the birds rapidly tapping their feet. To view this behavior, which is too fast for the human eye to perceive, researchers at the Max Planck Institute for Ornithology and Hokkaido University, led by biologist Nao Ota, recorded twenty pairs of courting birds with video cameras. The birds were observed in soundproof cages with perches and pieces of grass for nesting materials, which they often pick up and wave to begin their courtship displays.
To measure the effect of having an audience, the researchers recorded the pairs’ behavior with and without a third bird in an adjacent cage separated by a mesh screen. They found that, when courting, both male and female birds produced more song-and-dance displays with a third bird watching than with no audience—even though they never directed their displays at the audience. The researchers hypothesize that this is a way for birds to advertise their mating status to the outsider.
This audience effect was strongest when the third bird was the opposite sex of the bird performing the courtship display, suggesting that the increased display behavior signals commitment to the bird being courted. This idea is supported by the observation that courting birds seem to focus their attention on their partners by angling their tails toward them and perching next to them to dance.
Previous research has suggested that songs without dance can be interpreted as aggression. In this study, both males and females performed fewer song-only displays when an audience was present, perhaps to avoid conflict with potential competitors. (Science Advances)