A male hummingbird makes sounds with his tail feathers to attract females.
Dive-bombing hummingbirds. I’m Bob Hirshon and this is Science Update.
(Costa’s hummingbird dive sound)
When male Costa’s hummingbirds dive through the air, they sound a little like the onboard communications system in Star Trek. But they’re really just trying to impress females.
The males will climb high up in the air and then do this power dive where they descend and accelerate towards the earth and then zoom past the female while spreading their tail and making sounds with their tail as they go past.
UC Riverside biologist Chris Clark and his colleague Emily Mistick report in Current Biology that the males twist their tail feathers during flight to reduce sound distortion caused by the Doppler effect:
…Like a race car going by on a racetrack (neer-rowww).
This allows them to control their perceived speed, but it’s not yet known why they do this, or if the females take notice. I’m Bob Hirshon, for AAAS, the science society.
Making Sense of the Research
Unlike the male sex of many species, the male Costa's hummingbird likes to downplay his abilities in order to attract a mate. Many male animals perform athletic motor displays for females, who evaluate the males' performance when choosing a mate. Examples of this can be found among various species, including male bowerbirds that decorate their nests with flowers and other objects to impress potential mates, buff-breasted sandpipers that flash their wings and do a double-wing courtship display to woo their mates, and male peacock spiders use their decorative, colorful abdominal flaps to impress females. The complex display involves sending out vibratory signals, revealing a pair of black-and-white third legs, and waving their peacock-like flaps.
Male Costa's hummingbirds use several strategies to attract mates. They sing. They spread the iridescent feathers of their throats, transforming their heads into shiny, violet octopuses. And they fly up to tall perches to fall into acrobatic dives, shooting downward before pulling up at the last second. As they dive, they hold their tail feathers spread, causing the back edge of the outer tail feather to flutter in the airflow. This action produces a whistling sound, and the pitch of this sound could indicate to females how fast the males are traveling and how fit they are.
It is this last method that University of California, Riverside, biologists Chris Clark and Emily Mistick report on in Current Biology. In order to study the sound produced by the males' actions, Mistick tested feathers from the hummingbirds in a wind tunnel, which showed that the frequency of the whistle they produce is directly related to the airspeed around them. So, this means that the faster a male dives, the higher the pitch of his whistle. In addition, the pitch sounds higher than it is to females because of the Doppler effect, which makes an approaching noise sound higher pitched. One could assume, then, that the whistle would be an honest demonstration by the male of his abilities.
When Clark and Mistick filmed the hummingbirds, however, they found that the males seemed to have control over how they presented the whistle to potential mates. Instead of diving straight at the females and pulling up just above them, which would produce the most dramatic whistle with the highest perceived pitch, though, the males would dive to the side of the females. They also would make sure to spread out half of their tails and twist them toward the females, essentially aiming their speakers. This action, though, still has the effect of reducing the pitch. So, it looks like the males are hiding an indicator of their speed.
The scientists postulate that the males may do this to try to avoid being confused by the females with males from another hummingbird species—the Anna's hummingbird—which also dives but produces a lower pitch. They also think that the Costa's hummingbirds have developed this display for purely aesthetic reasons—the males dive not to show off their qualities but simply because the females like it.
Now try and answer these questions:
- What are some things that male animals will do to attract a mate?
- Name the three things that male Costa's hummingbirds do to attract mates.
- How did the scientists test the tail feathers to determine the frequency of the whistle in relation to airspeed?
- What is intriguing about how the males perform their dives?
- Why do the scientists think the males do this?
- What do you think is the reason for the male Costa's hummingbirds to dive the way they do?
You can listen to the Testosterone Tradeoff Science Update to learn how extra testosterone levels may give male birds advantages in mating but can also lead to other problems.
In the Birdsong and Climate Science Update, you can learn how birds that live in more variable climates sing more sophisticated songs.
You can use this Science Update with your students to help them learn about how different animal species use different strategies to reproduce and carry on their species. It could be used as the starting point for further research about animal reproduction and survival strategies.