A new analysis indicates that birds don't fly alone when migrating at night. Some birds, at least, keep together on their migratory journeys, flying in tandem even when they are 200 meters or more apart.
The study, from researchers at the University of Illinois and the Illinois Natural History Survey, appears this month in Integrative and Comparative Biology. It is the first to confirm with statistical data what many ornithologists and observers had long suspected: Birds fly together in loose flocks during their nocturnal migration.
Researchers have spent decades trying to determine how birds migrate at night, when most bird migration occurs. But nighttime tracking of tiny flying objects a quarter mile to a half mile up is no easy task. They have used stationary light beams, radar-mounted tracking spot lamps and long-range radar to try to figure out what is going on in the night sky. Some have even watched birds cross the face of the moon.
Decades of such observations suggested that birds travel together at night, but not in compact flocks as they do during the day, said principal investigator Ronald Larkin, a professor of animal biology, who conducted the new study with Robert Szafoni. Larkin is a wildlife ecologist with the Illinois Natural History Survey, where Szafoni also worked as a research scientist. Sfazoni currently is an affiliate of the INHS.
Previous studies "sometimes very strongly suggested that the birds were flying tens of meters apart and yet somehow keeping together," Larkin said. But the evidence for this was "indirect and suggestive," he said.
Even if it could be established that the birds were flying in groups, Larkin said, no one knew whether they were simply being swept along together passively or whether they were actively, intentionally, traveling together.
In the new analysis, the researchers took a fresh look at bird-flight data Larkin had collected in the 1970s and '80s
|Contact: Diana Yates|
University of Illinois at Urbana-Champaign