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Migration exhausting for birds

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By Debra Lyon-Dye

A good day for the birder is usually NOT a good day for the bird; so explained Dr. Doug Levey, ornithologist from the University of Florida, a Keynote Speaker for the Nature Coast Bird & Wildlife Experience.

Dr. Levey, in his presentation "The Challenges of Migration Across the Gulf of Mexico," revealed that one half of all birds migrate through the Gulf. Sometimes the weather helps them but it can also work against them, sending them east to Florida. The "lucky" arrive tired and starving, often on Seahorse Key, the first land they see. This is called Fallout. In this weakened state they are studied by Dr. Levey and his students.

Before migrating, birds fatten up in the fall, some doubling in mass. They "carb up" on fruit. Usually they fly at night at high altitudes as it is cooler. They use the stars, sun, innate homing skills, their internal clock and internal compass to navigate. Flocks leave together, call out to one another in flight, but fly at different speeds depending on their mass. They then land with their flock. Their bodies become smaller and smaller as they fly, even digesting part of their organs which they rebuild later. Some birds land along the way to rest and replenish. Others fly non-stop, the farthest known distance being some seven thousand miles. Some paths are direct routes, others loop, and still others make no sense at all.

Their primary peril is weather. Minor Fallouts occur frequently but every five to ten years there occurs what birders call a

"Spectacular Fallout." One occurred on April 21, 2007 but did not correspond with bad weather. The strangest thing according to Dr. Levey is that the bird fallouts often do not correspond to weather reports. Many in the field are trying to predict the fallouts. On April 21, 2007 Dr. Levey's team caught and studied over one hundred birds on Seahorse Key. The same thing happened on the same day at Ft. Desoto, Florida also a western point where tired birds will seek refuge. Many of the Fallout birds will survive, but many will not. Dr. Levey's team uses "mist netting" to trap the birds. They weigh, band and then release them.

As a side note, some are eaten by the numerous cottonmouths on Seahorse Key. Dr. Levey reminded the audience that the island enjoys the densest population of cottonmouths in North America.