(Inside Science) — The black-tailed tit whistles with two different accents on its wings, which could provide further evidence that the birds are two separate species, according to a new study.
Birds are famous for their ability to sing, but dozens of species use their feathers to make sounds. For example, peacocks can shake their feathers against each other, The wings of the pigeon make a whistling sound when flying..
In a new study, researchers looked at the forktail flycatcher, a one-ounce bird found throughout America that resembles a black and gray swallow. The males sport a foot-long, scissor-like tail that helps them attract mates, and they spread these huge feathers as air brakes to help them change direction rapidly when hunting, said study lead author Valentina Gomez-Bahamon, an evolutionary biologist at the Field Museum in Chicago.
When the birds fly — sometimes as fast as 65 miles per hour — they make a high-pitched squeak. Males often fly fast when they fight each other during mating season, Gómez-Bahamón noted. The birds also fly fast when they ward off intruders near their nests.
Scientists studied two subspecies of the forked-tailed tit: one that is migratory and breeds in southern South America but spends the winter closer to the equator, and one that is non-migratory and spends most of the year in the northern part of the continent.
The scientists first captured the birds using “fog nets,” a thin net stretched taut between two poles like a volleyball net, and recorded audio and video of the birds’ flight after they were released. The researchers also placed stuffed falcons with hidden cameras in the field, and when the forked-tailed flycatcher swooped down to attack, the researchers recorded how the flycatcher’s feathers moved and what sounds it made. The entire project took three years.
“It’s really hard to document a fast-flying fighter bird,” said Gomez-Bahamon. “It took a lot of trial and error.”
Audio and video footage and experiments using forked-tailed flycatcher feathers in wind tunnels have shown that the birds create these vibrations by fluttering their feathers. The airflow causes these feathers to vibrate in a short, repetitive whistling sound that is very similar to sound. You can also whistle using a blade of grass..
Gomez-Bahamon and her colleagues found that the migratory subspecies produced higher-pitched, vibrating sounds with their feathers than their non-migratory cousins.
Migrating males have thinner wing feather tips than their domestic brethren, which may have evolved to help them fly longer distances. The researchers suggest that migrating groups of fork-tailed flycatchers stopped migrating and, as they no longer traveled long distances, their wing feathers grew thicker and they began to produce a different sound than their migrating relatives.
“This is an incredibly difficult task. These birds are really airborne and untamed,” said Richard Prum, an evolutionary ornithologist at Yale University who was not involved in the study. “I was amazed at the level of detail in the analysis they were able to do.”
In addition to escapes and fights, males of both subspecies flap their wings in the early morning while it is still dark, perhaps to show off to females, Gómez-Bahamón said. The birds sing, then fall silent for a while before taking short flights in which a fluttering sound can be heard.
Since wing flapping can help the birds communicate during mating season, Gómez-Bahamon and her colleagues suggest that the plumage “accents” they discovered could help further separate the subspecies. Eventually, the two flycatchers could evolve into completely separate species that can’t interbreed. “Different migratory behaviors could lead to different behavioral traits,” Gómez-Bahamon said.
Future studies will investigate whether related species exhibit similar behaviors. Scientists will also look at whether female forked-tailed flycatchers prefer the sounds of male subspecies, Gómez-Bahamón said. Juan Ignacio Areta, an ornithologist at the Institute of Biological and Geosciences of Northwestern Argentina, who was not involved in the study, wonders how preventing the birds from fluttering their feathers might affect their mate choice. “Answering these interesting questions is difficult and requires a lot of carefully designed field experiments,” he said.
Scientists have explained in detail Their discovery In the journal on September 22nd Integrative and Comparative Biology.
Charles Q. Choi is a science journalist who has written for Scientific American, The New York Times, Wired, Science, Nature, National Geographic News, and others. Reprinted with permission. Inside ScienceAn editorially independent news product of the American Institute of Physics, a nonprofit organization dedicated to advancing, promoting, and supporting the science of physics.
