Thrush takes red-eye flight south

10/25/2003

And you think you're sleep deprived?

Those flocks stitching the horizon on their southbound flights probably won't sleep tonight. And they probably won't sleep tomorrow night either, if the weather remains clear.

In fact, marathon migrators like the Swainson thrush, which begin no further south than Michigan's Upper Peninsula and keep going until they cross the Gulf of Mexico, probably pull more all-nighters than your average conscientious college student during exam week - maybe almost as many as new mothers with colicky babies.

So, how do they do it? (The birds, not the mothers - although there's a topic that ought to garner rich government funding.) Verner Bingman, a Bowling Green State University professor who often focuses on pigeon navigation, and doctoral student Thomas Fuchs, are trying to figure that out.

“These birds are typically diurnal, which means they're active during the day,'' Dr. Bingman said. “Yet twice a year for a few weeks, they totally change their lifestyle. A vast majority of songbirds migrate at night.'' If migrating birds are active in the morning, they're probably just finishing the night's commute. The rest of the day, they eat, they hang out. They might watch the soaps if Guiding Light featured cute warblers more often.

The scientists' first guess - maybe even their initial hope - was to see the Swainson thrush execute an enviable trick called unihemispheric sleep.

Talk about your valuable skills.

Marine mammals and plenty of birds

can let half their brain nap while the other half thinks about whatever birds - or dolphins - think about. Such a skill would come in handy on long trips, or if you need to keep breathing while you swim.

The Swainson thrush could really use it on its 12 to 14-hour jaunt across the Gulf of Mexico that simply allows no rest stops - their other need for rest stops being obliterated by indifferent notions of privacy and hygiene.

So the research team gathered some Swainson thrushes, put them in a cage, and videotaped them.

The impulse for migration is so strong, the confinement of a cage doesn't dampen it. The captives simulate migration, growing active at night instead of during the day. They'll even hop south in the fall and north in the spring.

But researchers were looking for the biggest sign of unihemispheric sleep: a single closed eye.

“After looking at 100s of hours of videotape, we don't see it,'' Dr. Bingman said, leading the researchers to conclude the half-brain sleep strategy probably contributes little to the thrush's nocturnal wanderings.

What they are seeing is change in daytime behaviors.

“There is a substantial reduction in the occurrence of nonspecific behaviors, whereas specific behaviors like feeding, singing, and preening, don't change,'' he said.

In other words, the birds are resting up.

In the next stage of research, Mr. Fuchs will attach electrodes to the birds' brains to see if the birds are resting half a brain without closing their eyes.