This Bird Communicates by Fluttering its Feathers

Researchers have long known that birds communicate by a variety of sounds. But in addition to chirping and hooting, the fork-tailed flycatcher talks with other birds by fluttering its feathers.

The fork-tailed flycatcher (Tyrannus savana) is a passerine (perching) bird normally found from southern Mexico through Central America, and into much of South America. The male of the species makes unusual sounds by fluttering its feathers at high frequencies, researchers found in a new study.

“We captured these birds for other projects and noticed that when we released them, males made these fluttering sounds,” lead author Valentina Gómez-Bahamón, a researcher at Chicago's Field Museum and a PhD student at the University of Illinois at Chicago, tells Treehugger. “Also, males have shape modifications in their flight feathers and based on the literature, we knew that some birds with feather modification produce sounds. We didn't know by which mechanism or under what behavioral context these sounds were produced.”

The black and gray birds have foot-long scissors-shaped tails that they use to attract mates. They also spread their tails wide when they are soaring around, hunting for insects to eat.

But it’s the feathers in their wings, not their tails, that they use to make their unusual communication noise.

“I think fluttering is the best word that describes the sound. It sounds like a brr-r-r-r-r-r-r-r-r whenever the birds are flying fast,” Gómez-Bahamón says.

The study was published in the journal Integrative and Comparative Biology.

The researchers wanted to make sure that the sounds were indeed coming from the birds’ feathers and not actually vocalizations. To study the birds’ sounds, researchers captured birds with mist netting (which is fine webbing stretched between poles like a volleyball net), and recorded audio and video of the birds as they flew away. They found the birds only made sounds in certain instances.

“When they wake up and are singing in their territories, they move short distances from branch to branch producing this feather sound,” Gómez-Bahamón says. “They also make this sound when they reach a threshold velocity, which happens when they are fighting each other, attacking predators, or ‘escaping’ when we release them after capture.”  

Although fork-tailed flycatchers are very tiny, they are territorial and fight a lot. They will fight off much larger birds that approach their nests, including hawks that are more than 10 times their size. During mating season, males often battle one another.

To get an ever better idea what the bird looks and sounds like when fighting, the researchers outfitted a taxidermy hawk with a hidden camera and microphones. They recorded how the feathers moved and the sounds they made when the flycatcher swooped in to attack the hawk, shown above.

They Have Different Accents

There are at least two subspecies of this specific flycatcher, one that spends the whole year in the northern part of South America and another that migrates long distances. The recordings showed a difference in the fluttering sounds made by the two subspecies. Gómez-Bahamón likens it to different dialects or accents.

“They differ in the frequency at which they produce the br-r-r-r-r-r-r sound,” she says. “Migrants have a higher pitch brr-r-r-r-r-r-r-r-r while non migrants have a lower pitched one. We still don't know if they can discriminate between each other.”

Because the birds use their wing noises to communicate with each other, having a language barrier between species might be an issue for mating.

Non-verbal communication has been observed in other birds and researchers suspect that it may be more prevalent than previously thought. 

“These detailed studies are very important for us to understand nature. The more we know about the natural history of many species, the more we can ask comparative questions and understand nature as a whole,” Gómez-Bahamón says. “I see this study as a building block, and I really hope I get to study more species in this kind of detail.”