(Inside Science) — A new study suggests that yellow-winged skylarks have two distinct accents on their wings, which could provide further evidence that the bird has split into two species.
Birds are known for their songs, but dozens of bird species also use their wings to make sounds – peacocks, for example, make sounds by beating their feathers. The wings of the Crested Pigeon make a whistling noise when flying..
In the new study, researchers looked at chicken flycatchers, a 1-ounce bird that resembles a black-and-gray swallow and lives throughout the Americas. Males have foot-long, scissor-shaped tails as an ornament to attract females. They also spread their enormous wings to help them make tight turns when hunting, using their feathers as air brakes, said Valentina Gomez-Bahamon, an evolutionary biologist at Chicago’s Field Museum and lead author of the study.
These birds fly at speeds sometimes reaching 65 miles per hour and make a high-pitched trilling noise, and Gomez-Bahamon said males often fly quickly when fighting each other during mating season, as well as when fighting intruders near their nests.
The scientists studied two known subspecies of the narcissus flycatcher: a migratory bird that breeds in southern South America but spends the winter closer to the equator, and a non-migratory bird that spends the year in the northern part of the continent.
The scientists first captured the birds in mist nets, thin mesh that is stretched between two poles like a volleyball net, and then released them to record audio and video as they flew away. The researchers also set up a stuffed hawk in the field with a hidden camera to record the birds’ movements.
“Filming fast-flying fighting birds is really difficult,” Gómez Bahamón said. “It took a lot of trial and error.”
Audio and video footage, as well as tests of flycatcher wings in a wind tunnel, have revealed that the birds produce these trills by flapping their wings: air currents cause these feathers to vibrate in short, repeating whistling sounds. Can whistle using blades of grass.
Gómez-Bahamón and her colleagues found that migratory bird subspecies produce higher-pitched wing beats than their non-migratory counterparts.
Migratory males have feathers with thinner tips than their nest-bound cousins, which may have evolved to make it easier to fly long distances. The researchers speculate that as migratory Narcissus flycatchers stopped migrating and no longer flew long distances, their feathers became thicker and their calls became different from those of their migratory cousins.
“This is a very difficult study. These birds are actually flying, and they’re not domesticated,” said Richard Plumb, an evolutionary ornithologist at Yale University who was not involved in the study. “I was amazed at the level of detail they were able to provide.”
Besides fleeing and fighting, males of both subspecies beat their wings in the early hours of the morning while it is still dark, probably as a display for females, Gómez-Bahamón said. The birds sing, are quiet for a while, and then perform a short flight where you can hear the flapping of their wings.
Because wing flapping may help the birds communicate during mating season, Gómez-Bahamón and his colleagues suggest that the feather “accents” they discovered may help further separate the subspecies. Eventually, the two flycatchers may evolve into completely separate species that can’t mate with each other. “Differences in migratory behavior could spill over into other behavioral traits,” Gómez-Bahamón said.
Future studies will investigate whether closely related species exhibit similar behavior. Gómez-Bahamón says scientists also plan to investigate whether female flycatchers prefer the calls of males of the subspecies. Ornithologist Juan Ignacio Areta of the Institute of Biogeology of Northwest Argentina, who was not involved in the study, wonders how blocking birds’ wingbeats might affect mate choice. “These are interesting questions that are difficult to answer and require many carefully designed field experiments,” Areta said.
The scientists detailed Their findings September 22nd Journal Integrative and Comparative Biology.
Charles Q. Choi is a science reporter whose work has appeared in Scientific American, The New York Times, Wired, Science, Nature, and National Geographic News. Inside the Scienceis an editorially independent news product of the American Physical Society, a not-for-profit organization dedicated to advancing, promoting, and contributing to the physical sciences.