Need Sleep? Birds May Have Shortcut to Second Wind

Bijal P. Trivedi
National Geographic On Assignment
November 12, 2003
Siestas aren't just for people, say scientists who have found a
promising new subject for their research: migratory birds.

During the migration season, these long-distance travelers feed during the day and fly by night to avoid predators and take advantage of the calmer atmosphere—at the cost of sleep.

The solution for Swainson's thrush (Catharus ustulatus), as for sleep-deprived humans on a long haul, may be to give up some leisure time and take a nap.

"Migratory birds abandon normal sleep patterns and don't seem to experience negative consequences," said Verner Bingman, a behavioral neuroscientist at the J. P. Scott Center for Neuroscience, Mind, and Behavior at Bowling Green State University in Ohio.

Bingman and his colleague Frank Moore, an eco-physiologist at the University of Southern Mississippi in Hattiesburg, are investigating how bird behavior and brain activity change during migration, and how birds make up for sleep loss. The National Science Foundation in Arlington, Virginia, has awarded U.S. $20,000 for the research.

The scientists hope that their findings will apply to sleep-deprived humans, too—military personnel, pilots, truck drivers, business travelers, and anyone who works the night shift, regularly crosses time zones, or works long hours. An estimated 25 to 35 million Americans suffer from sleep disorders, and another 35 million are sleep-deprived.

Sleeping with Half the Brain

Bingman, Moore, and Bowling Green graduate student Thomas Fuchs have concentrated on Swainson's thrush, a greenish-brown migratory bird that breeds in the coniferous forests of Alaska, southern Canada, northern California, Michigan, New England, and Newfoundland.

In the fall, the thrush flies as far south as Peru and Ecuador, where it winters—at least a 3,000-mile (4,800-kilometer) journey that includes a nonstop 16-hour flight across the Gulf of Mexico.

These birds are particularly convenient experimental subjects. As it happens, the birds show migratory behavior even if they never leave the lab. In a circular cage, "they face and hop south in fall and north in spring," Bingman said.

During non-migratory seasons the birds are active during daylight and sleep at night. But as fall approaches and the days become shorter the birds begin to eat more—putting on weight before their migration—and experience "nocturnal restlessness" during which they hop around at night.

In effect, the birds are seasonally sleepless, according to Bingman: "[They] are a natural model of sleep deprivation."

"Animals can vary the amount of sleep as the seasons change," said Jerome Siegel, neuroscientist and professor of psychiatry at the University of California at Los Angeles Medical Center and the Sepulveda Veterans Affairs Medical Center. "If we understand what sleep is doing to their brains then we may be able to manipulate the neurochemistry in the human brain to do something similar someday."

Birds are known for their ability to handle sleep deprivation—better than any mammal. Pigeons, for example, can survive for months with only about ten percent of their normal sleep time.

Micro Naps During Flight?

Other animals have evolved sleep styles suited to their life patterns. Dolphins and fur seals are so-called unihemispheric sleepers: They continue to swim and breathe while half the brain sleeps and the other half remains active.

One initial hypothesis, said Bingman, was that Swainson's thrush uses unihemispheric sleep, a form also observed in many birds: one eye remains open while the other is closed.

The hypothesis was that the birds flew great distances by alternately resting each hemisphere of their brain.

But after preliminary experiments, Bingman suspects that unihemispheric sleep is not the primary way the thrushes handle sleep loss.

"I did occasionally see one eye closed and one eye open but not for the periods I would have expected," said Fuchs. He plans to use an electroencephalogram to measure activity within each hemisphere of the brain to further explore this hypothesis.

To Bingman, the most extraordinary, though preliminary, finding is how the birds change their daily routine during migration season: They were less active and took naps. "They would squint their eyes and fluff their feathers—a sign of drowsiness," said Bingman.

These naps—though only about a minute long—enable the thrush to spend about ten to 15 percent of the day during the migration period in a sleep or sleep-like state. These sleep postures are rare in the non-migration season when the birds only spend two to three percent of their day sleeping. "We think that these naps are critical for combating sleep deprivation."

"Maybe they take micro-naps during flight," Bingman said.

To make time for these naps the thrushes give up what Bingman characterizes as exploratory or play behavior.

"They feed as much, groom as much, sing as much, but they don't do things that waste time or have marginal importance. They do their chores but they give up their play time, to take naps," said Bingman.

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