Do migratory birds sleep in flight? Neuroscientists seek answer

But some birds make similar—and longer—migrations every year, abandoning their typical nighttime sleep pattern to turn nocturnal for a few weeks in the spring and fall.

How they do it—perhaps literally half-awake—and especially how they compensate for the lack of sleep to keep their biological systems functioning, is what a Bowling Green State University neuroscientist hopes to learn through new research.

Dr. Verner Bingman, a professor of psychology, has received a $20,000 grant from the National Science Foundation to conduct the study with Dr. Frank Moore, a professor and chair of biological sciences at the University of Southern Mississippi.

If they can learn something from what Bingman called “a natural model of sleep deprivation,” it might be applicable to humans, including nightshift workers and military personnel who are deployed across time zones and expected to be combat ready, he said.

Bingman, who has previously studied homing pigeons, said he and Moore are using Swainson thrushes for the sleep study because the birds are common, reasonably large and “their migrations are impressive.” The greenish-brown birds breed in northern Michigan, New England and Canada but winter as far south as Peru and Ecuador, forsaking sleep for 12-14 hours to cross the Gulf of Mexico alone, he noted. On the first cool night of fall, he added, the thrushes might be seen in residential neighborhoods in northwest Ohio as they’re making their way south.

The researchers are addressing physiology in the dozen or so thrushes that Moore is capturing along the Gulf Coast of Mississippi and sending to Bowling Green for study. They will use an electroencephalogram (EEG) to determine whether there are changes in brain wave activity from a typical sleep pattern to a time of wakefulness during migration.

Migratory behavior can be simulated even in a laboratory setting, Bingman pointed out. “The birds do it on their own when the light-dark cycle—the amount of daylight—indicates it is a season for migration.”

In addition to studying physiology, the researchers will observe the birds’ behavior. They will be videotaped, and frequency of behaviors—especially sleep behaviors—will be recorded, Bingman said, noting that criteria have been devised to determine whether the birds are sleeping. “Believe it or not, this is more complicated than simply eyes being open or closed,” he said.

Closed eyes are still the first way of telling if a bird is asleep, added Thomas Fuchs, Bingman’s graduate assistant. “But birds also adopt typical sleeping postures which can vary between species,” Fuchs said. “These sleeping postures might also provide some information about sleep quality, which is why they are especially interesting for us.”

Swainson thrushes sleep on perches, either with their bills resting on their chests or in a position with their bills facing backward. In that position, the eyes are hidden under the feathers; it has mistakenly been called the “head under wing position” because it looks like the bird is hiding its head under a wing, Fuchs said.

If a bird has one eye open and the other closed, it may be in the “truly extraordinary” state of unihemispheric sleep, Bingman said. This phenomenon is common in marine mammals such as whales and dolphins, which would drown if fully asleep, he said. It has also been described in many species of birds behaviorally and physiologically—with one side of the brain indicating electrical activity of wakefulness and the other, of sleep—but never in the context of migration, according to the BGSU neuroscientist.

Determining whether birds sleep during flight will require simultaneous monitoring of the eyes and activity in both hemispheres of the brain. “Behavioral data and EEG data will have to come together at some point to give us a good idea of what’s really going on,” Fuchs said.

The NSF grant is for one year, but evidence of success in identifying the birds’ adaptations to nocturnal activity will enable the researchers to pursue further funding, said Bingman. The collaboration is his first formal one with Moore, whose research focus is migratory birds.

Bingman is founding director of BGSU’s J.P. Scott Center for Neuroscience, Mind and Behavior, where investigators study the dynamic relationships between the nervous system and behavior. More than two dozen professors from universities nationwide are affiliated with the center, which opened in 1999.

(Posted October 08, 2003 )