Most health-conscious people try to get rid of unwanted fat. But, for billions of migratory songbirds preparing to head south for the winter, a fat body is essential.
Without sufficient body fat, many of the birds — some of which began leaving this month — will perish during the fall migration, running out of energy well before they make it to their winter homes in the southern tropics.
Fat is the fuel that powers their arduous trip. At departure time, fat will account for up to 50 percent of the weight of Georgia’s long-distance migratory songbirds, such as warblers, thrushes, flycatchers, swallows, grosbeaks, vireos, orioles, tanagers and ruby-throated hummingbirds.
After nesting in North America during the summer, most migratory birds will spend the winter in Mexico and Central America. Many, though, will continue flying further south. A scarlet tanager that spent this summer in Georgia, for instance, may go on to Brazil.
While flying over land, most of the birds will make several stops along the way to rest for a day or two and feed voraciously to restore depleted body fat. An average songbird may stop every 165 miles during southbound migration.
Bird experts call the resting and refueling places “stopover areas,” where birds can find shelter from predators and abundant insects, berries, fruits and other fat-building food.
Thus, stopover areas are vitally important for helping songbirds reach their destinations. That’s especially true of stopover areas along the Gulf of Mexico. That’s where waves of songbirds now leaving Georgia and elsewhere in North America will launch themselves and fly nonstop for 500-600 miles over water before making landfall in Mexico.
Birds that fail to gain sufficient weight won’t make it across the Gulf — a major reason why some 50 percent of the southbound songbirds won’t return to North America next spring to nest.
Unfortunately, stopover areas themselves are in peril, succumbing to relentless development and other problems. For migrating songbirds, it’s another in an already long list of threats to their survival.
In the sky: From David Dundee, Tellus Science Museum astronomer: The moon will be first-quarter by next weekend. Mercury is low in the west at dusk and will appear near the moon Saturday night. Saturn is in the southwest at dusk and sets in the west just after midnight. The other planets can't easily be seen right now.
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