April 12 (UPI) -- Male Costa's hummingbirds don't use their pipes to serenade would-be mates, they use their tail feathers. In a new study, scientists found male hummingbirds aim their dives to the sides of females in order to minimize the Doppler effect.
The vibrations created as air flows across the tail features of a diving male Costa's hummingbird produce a song of sorts. The musical dive is the male's way of showing off in front of females, a mating display.
New analysis of the display suggests males position their dives to the side so that females can't use the Doppler effect to determine the speed of their dives.
"Recent studies in birds and other animals suggest that females prefer higher speeds during male athletic displays," Christopher Clark, an assistant professor of biology at the University of California, Riverside, said in a news release. "By concealing their speed, males are not necessarily cheating, but instead have evolved this placement of trajectory out of female choice."
While diving to the side of females, males twist some of their tail feathers up to 90 degrees to aim their song at potential mates.
"We don't know why males twist only half of their tails toward the females, but it may be due to anatomical limitations that prevent them from twisting their whole tail around," Clark said.
Researchers recorded diving males in the wild and also tested the sounds produced by vibrating tail feathers in a wind tunnel. Clark and his colleagues had difficulty estimating the speed of the bird's dive using the recorded vibrations.
"Once I realized it wasn't trivial for a scientist to measure, I realized it wouldn't be trivial for a female to measure either," Clark said.
While many studies have focused on static mating displays, bright colors and uniquely shaped feathers, the nest study -- published this week in the journal Current Biology -- highlights the importance of dynamic, athletic mating displays.