In the world of Costa's hummingbirds, the important thing is not the size, it's the sound. During the breeding season, Costa males perform a high-speed dive during which they "sing" to potential partners using their tail feathers.
Unlike the related hummingbird species, Costa performs his dives next to the females, instead of in front of them. In an article published today in Current Biology researchers at the University of California at Riverside show that this trajectory minimizes an audible Doppler sound that occurs when the Coast submerges. The Doppler effect is familiar to most people when the tone of an ambulance siren changes when the vehicle passes.
The findings suggest that men can strategically manipulate the way women perceive their screens by minimizing Doppler sound. This deprives women of an acoustic indicator that would reveal the speed of their dives.
"Recent studies in birds and other animals suggest that females prefer higher speeds during male athletic exhibitions.While hiding their speed, males do not necessarily cheat, but instead have evolved this location out of the path of choice female, "said Christopher Clark, who led the study. Clark is an assistant professor of biology at the Faculty of Natural and Agricultural Sciences of the UCR.
Clark and co-author Emily Mistick, a former UCR research assistant, showed that males point their sound toward potential pairs by rotating their tails vertically up to 90 degrees. In previous research, Clark has shown that the song of the tail is made by the flapping of the outer feathers of the tail.
"We do not know why males twist only half of their tails towards females, but it may be due to anatomy" This video uses a slow exposure acoustic chamber to show two dives to a female in a cage (below) ), using color to represent volume (loudness), "said Clark.
Clark and Mistick used a device called an acoustic camera to record dives of Costa also conducted experiments in a wind tunnel to examine how the birds' speed and direction influence the sounds they emit, and interestingly, they discovered that it was difficult to measure the speed of Costa's immersion from the sound produced.
"Once I realized that it was not trivial for a scientist to measure, I realized that it would not be trivial for a woman to measure," Clark said.
Clark said the findings add to the literature on how males use athletic displays to attract females.
"Most research has focused on static male attributes, such as bright colors or elongated tails, but our research shows that dynamic displays can be just as important, and men strategically control these performances to show themselves to be the best possible way, "Clark said.
How hummingbirds produce fluttering sounds during courtship
"Acoustic strategic control of a hummingbird courtship dive" Current Biology (2018). DOI: 10.1016 / j.cub.2018.03.021