Wednesday, September 12, 2007

When Do Migratory Birds Sleep?

The majority of songbirds migrate at night, flying for as long as five to seven hours at a stretch. And as birdwatchers know, migrants are quite active for at least several hours each morning at stopover sites.

Upon touchdown, migrants must find food to fuel their long flights, and they have to find it at unfamiliar sites, often amid lots of competition from resident birds and other migrants. Migrants that are particularly fat-depleted or that find themselves in a stopover site with poor resources may have to forage longer than migrants in better condition or at a better

During migration, birders often notice a lull at mid-day, which is apparently the time when many migrants rest or sleep. Birds then forage again in late afternoon or early evening before departing on the next leg of their journey. Considering that the rest of the year most songbirds sleep perhaps five to ten hours a night, depending on the season, their change of schedule leaves little time for sleep.

Recent neurological studies found that migrating birds spend about two-thirds less time sleeping than when they are not migrating. Yet they navigate long flights and find food, water, and shelter in novel environments.

The same level of sleep deprivation in other animals usually results in reduced cognitive function. A study using captive White-crowned Sparrows, however, found that they performed just as well on food-acquisition tasks during migratory seasons, when they had much less sleep, as they did in non-migratory periods.

How birds can function so well with so little sleep is not known. It is another one of the amazing adaptations that have allowed birds to adopt a migratory lifestyle. Find more at Birder's World website.

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