[TN-Bird] Birds Napping While Migrating?

From: "Charles Nicholson" <cpnichol@xxxxxxxxxxxxx>
To: <tn-bird@xxxxxxxxxxxxx>
Date: Mon, 10 Nov 2008 20:19:22 -0500
Following is an article from the AAAS ScienceNOW Daily News Service which I
think will interest most readers.
 
Bird Brains Split Lookout Duty


By Michael Price
ScienceNOW Daily News
6 November 2008

What good is half a brain? Good enough for migratory birds to avoid
predators when napping in the daytime. A new study finds that migrating
birds take mini-naps during the day but only rest half their brains at a
time, allowing them to keep one eye open. 

Many migrating birds fly at night-- often, all night--to cut the risk of
being seen by predators and to avoid overheating under the hot sun. Some of
these flights are long, especially when crossing ecological barriers such as
the Gulf of Mexico, says Frank Moore, a biologist at the University of
Southern Mississippi, Hattiesburg. Sometimes, birds fly continuously for 24
hours. "That necessarily means they get less sleep when migrating," he says.


Weary birds face risks when they stop to rest along the way. Similar to
people, sleep loss makes birds less vigilant, which leaves them vulnerable
to predators. How birds manage to fly all night and not get eaten when they
stop for the day hasn't received much attention from scientists, Moore says.
"The problem just hadn't occurred to most people." 

Moore and colleagues decided to answer the question by putting seven captive
Swainson's thrushes, which are normally active in the day but fly at night
during migration, into a cage and providing artificial sunrises and sunsets
to mimic the migratory season. The scientists also implanted electrodes to
monitor the birds' brain activity. 

Occasionally, the birds would droop and seem drowsy for a few seconds but
then kick back into wakefulness. During these mini-naps, they'd often close
only one of their eyes. When researchers looked at their brain activity
during these times, they saw that one hemisphere of the brain had electrical
patterns resembling nighttime sleep, whereas patterns from the other
hemisphere indicated wakefulness. The researchers, who published their
findings online this week in Biology Letters, concluded that the birds were
resting half of their brains at a time in order to catch up on sleep while
staying on guard. 

The findings make sense to Doug Levey, an ecologist at the University of
Florida, Gainesville. "If you're a bird and you're mentally not very sharp,
there will be serious consequences," he says. Half-brain sleeping has also
been documented in marine mammals such as dolphins and whales, he says, so
it could be a convergent solution to a similar problem. Levey's not
convinced that the mini-naps compensate for lost sleep, though. "There are
other explanations that could account for [the behavior]," he says, such as
the birds' conserving energy by resting half their brains. 

Charles Walcott, a neurobiologist at Cornell University, says he's "always a
little suspicious" of electrical brain activity studies, because it can be
difficult to tease out what's sleep and what isn't. He'd like to see the
researchers use stricter quantitative standards to decide if an electrical
signal represents sleep. 

Chuck Nicholson
Norris, TN



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[TN-Bird] Birds Napping While Migrating?

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