One song isn’t enough for this vibrant little bird – the males have a secret second song
Costa’s hummingbird is native to the western edge of North America, where glimpses of the male’s iridescent violet plumage can be spotted as the tiny birds dart between flowers. All Costa’s hummingbirds rely on nectar, but the males especially need to keep their strength up when it’s time to start wooing the ladies. Their courtship involves some pretty standard calling, posing and feather-fluffing, but they’ve got a surprising skill; they sing with their tails.
Males dive past perched females at high speed, swooping from high branches in a direction that shows off their shining plumage. Over a certain speed, their outermost tail feathers begin to flutter, producing a high-pitched whistle. Keen to give a memorable performance, they even angle half of their tail so that the sound is directed right at the object of their affection.
Males of other hummingbird species dive over the females, but male Costa’s hummingbirds whiz past their audience on one size. Scientists have worked out that this draws out the sound and reduces the Doppler effect – the change in pitch when something is moving, like the siren of a high-speed ambulance – on their tail song.
In many courtship displays, males convey information about their strength, status or health. Strangely, these males have developed a tactic that makes it harder for females to judge the speed a male is travelling at, reducing any advantage a fit and fast bird would have in the pursuit of a mate. The researchers studying the species aren’t sure why they do this.
One suggestion is that the whistle isn’t really about impressing the females at all – it’s just a way to let them know they’re members of the same species. It could also be that the males aren’t trying to give information about their fitness, they’re simply trying to dazzle the females with their daredevil displays.
Photo: Joshua Tree National Park/flickr