When the going gets rough, the tough apparently sing slower.
As vegetation reclaimed formerly cleared land in California, Oregon and Washington over the last 35 years, male white-crowned sparrows have lowered their pitch and slowed down their singing so that their love songs would carry better through heavier foliage.
"This is the first time that anyone has shown that bird songs can shift with rapid changes in habitat," says biologist Elizabeth Derryberry who made the finding as part of her dissertation research at Duke University.
She compared recordings of individual birds in 15 different areas with some nearly forgotten recordings made at the same spots in the 1970s by a California Academy of Sciences researcher, and found that the musical pitch and speed of the trill portion of the sparrows' short songs had dropped considerably. "I was really surprised to find that songs had changed in a similar way in so many different populations."
She then used archival aerial photography to see how the foliage had changed in a subset of those spots, and found that the one population whose song hadn't slowed down lived in an area where the foliage hadn't changed either.
The physics is clear, but the biology is a little less certain. A lower, slower song suffers less reverberation in denser foliage and will be heard more accurately. In turn, that means it is more likely to be copied by young males who are choosing which song they will learn. Over generations, that should cause the song to slow down and drop in pitch as the foliage changes.
In the short term however, Derryberry doesn't know whether the clearer song wins better territories or mates, although she does know that these changes in song do affect both male and female behavior.
The results add to a growing body of evidence that the acoustic and visual communications of animals change with their habitat. "Given how much the world's habitats are changing, this is sort of an unexpected but useful factor to monitor," Derryberry said. She's now testing the broader effects of ecology on song evolution in birds across areas of South America where habitat may be changing due to deforestation and global warming.
Derryberry, who earlier discovered that female white-crowned sparrows preferred the slower new songs to the chirpy old ones, is now a researcher at Louisiana State University. Her latest findings appear in the July edition of American Naturalist.
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Showing posts with label songbirds. Show all posts
Showing posts with label songbirds. Show all posts
Friday, May 29, 2009
Wednesday, February 18, 2009
Songbirds Fly Three Times Faster than Expected
A York University researcher has tracked the migration of songbirds by outfitting them with tiny geolocator backpacks – a world first – revealing that scientists have underestimated their flight performance dramatically.
"Never before has anyone been able to track songbirds for their entire migratory trip,” said study author Bridget Stutchbury, a professor of biology in York’s Faculty of Science & Engineering. “We’re excited to achieve this scientific first.” Songbirds, the most common type of bird in our skies, are too small for conventional satellite tracking.
Stutchbury and her team mounted miniaturized geolocators on 14 wood thrushes and 20 purple martins, breeding in Pennsylvania during 2007, tracking the birds’ fall takeoff, migration to South America, and journey back to North America. In the summer of 2008, they retrieved the geolocators from five wood thrushes and two purple martins and reconstructed individual migration routes and wintering locations.
Data from the geolocators indicated that songbirds can fly in excess of 500 km (311 miles) per day, reports Stutchbury in the Feb. 13 issue of the journal Science. Previous studies estimated their flight performance at roughly 150 km (93 miles) per day.
The study, funded in part by the National Geographic Society, found that songbirds’ overall migration rate was two to six times more rapid in spring than in fall. For example, one purple martin took 43 days to reach Brazil during fall migration, but in spring returned to its breeding colony in only 13 days. Rapid long-distance movement occurred in both species, said Stutchbury.
“We were flabbergasted by the birds’ spring return times. To have a bird leave Brazil on April 12 and be home by the end of the month was just astounding. We always assumed they left sometime in March,” she said.
Researchers also found that prolonged stopovers were common during fall migration. The purple martins, which are members of the swallow family, had a stopover of three to four weeks in the Yucatan before continuing to Brazil. Four wood thrushes spent one to two weeks in the southeastern United States in late October, before crossing the Gulf of Mexico, and two other individuals stopped on the Yucatan Peninsula for two to four weeks before continuing migration.
The geolocators, which are smaller than a dime, detect light, allowing researchers to estimate birds’ latitude and longitude by recording sunrise and sunset times. The devices are mounted on birds’ backs by looping thin straps around their legs. The weight of the geolocator rests at the base of the bird’s spine, so as not to interfere with its balance.
Stutchbury credits researchers with the British Antarctic Survey for miniaturizing the geolocators. “They hadn’t really been thinking of [attaching them to] songbirds, but when I saw the technology, I knew we could do this,” she said.
The study also uncovered evidence that wood thrushes from a single breeding population did not scatter over their tropical wintering grounds. All five wood thrushes wintered in a narrow band in eastern Honduras or Nicaragua.
“This region is clearly important for the overall conservation of wood thrushes, a species that has declined by 30 percent since 1966,” said Stutchbury. “Songbird populations have been declining around the world for 30 or 40 years, so there is a lot of concern about them.”
She emphasized the importance of this research not only to protect at-risk species of songbirds, but also to gauge environmental concerns.
“Tracking birds to their wintering areas is also essential for predicting the impact of tropical habitat loss and climate change,” she said. “Until now, our hands have been tied in many ways, because we didn’t know where the birds were going. They would just disappear and then come back in the spring. It’s wonderful to now have a window into their journey.”
The study, “Tracking long-distance songbird migration using geolocators,” was co-authored by Tyler Done, Elizabeth Gow and Patrick Kramer (York University graduate students), John Tautin (Purple Martin Conservation Association), and James Fox and Vsevolod Afanasyev (British Antarctic Survey).
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"Never before has anyone been able to track songbirds for their entire migratory trip,” said study author Bridget Stutchbury, a professor of biology in York’s Faculty of Science & Engineering. “We’re excited to achieve this scientific first.” Songbirds, the most common type of bird in our skies, are too small for conventional satellite tracking.
Stutchbury and her team mounted miniaturized geolocators on 14 wood thrushes and 20 purple martins, breeding in Pennsylvania during 2007, tracking the birds’ fall takeoff, migration to South America, and journey back to North America. In the summer of 2008, they retrieved the geolocators from five wood thrushes and two purple martins and reconstructed individual migration routes and wintering locations.
Data from the geolocators indicated that songbirds can fly in excess of 500 km (311 miles) per day, reports Stutchbury in the Feb. 13 issue of the journal Science. Previous studies estimated their flight performance at roughly 150 km (93 miles) per day.
The study, funded in part by the National Geographic Society, found that songbirds’ overall migration rate was two to six times more rapid in spring than in fall. For example, one purple martin took 43 days to reach Brazil during fall migration, but in spring returned to its breeding colony in only 13 days. Rapid long-distance movement occurred in both species, said Stutchbury.
“We were flabbergasted by the birds’ spring return times. To have a bird leave Brazil on April 12 and be home by the end of the month was just astounding. We always assumed they left sometime in March,” she said.
Researchers also found that prolonged stopovers were common during fall migration. The purple martins, which are members of the swallow family, had a stopover of three to four weeks in the Yucatan before continuing to Brazil. Four wood thrushes spent one to two weeks in the southeastern United States in late October, before crossing the Gulf of Mexico, and two other individuals stopped on the Yucatan Peninsula for two to four weeks before continuing migration.
The geolocators, which are smaller than a dime, detect light, allowing researchers to estimate birds’ latitude and longitude by recording sunrise and sunset times. The devices are mounted on birds’ backs by looping thin straps around their legs. The weight of the geolocator rests at the base of the bird’s spine, so as not to interfere with its balance.
Stutchbury credits researchers with the British Antarctic Survey for miniaturizing the geolocators. “They hadn’t really been thinking of [attaching them to] songbirds, but when I saw the technology, I knew we could do this,” she said.
The study also uncovered evidence that wood thrushes from a single breeding population did not scatter over their tropical wintering grounds. All five wood thrushes wintered in a narrow band in eastern Honduras or Nicaragua.
“This region is clearly important for the overall conservation of wood thrushes, a species that has declined by 30 percent since 1966,” said Stutchbury. “Songbird populations have been declining around the world for 30 or 40 years, so there is a lot of concern about them.”
She emphasized the importance of this research not only to protect at-risk species of songbirds, but also to gauge environmental concerns.
“Tracking birds to their wintering areas is also essential for predicting the impact of tropical habitat loss and climate change,” she said. “Until now, our hands have been tied in many ways, because we didn’t know where the birds were going. They would just disappear and then come back in the spring. It’s wonderful to now have a window into their journey.”
The study, “Tracking long-distance songbird migration using geolocators,” was co-authored by Tyler Done, Elizabeth Gow and Patrick Kramer (York University graduate students), John Tautin (Purple Martin Conservation Association), and James Fox and Vsevolod Afanasyev (British Antarctic Survey).
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