Why Do Animals Migrate?
Birds do it, bees do it, dragonflies and manatees do it. But why?
by Amy Leinbach Marquis

(NAPSA)-Imagine swimming 7,500 miles to give birth to your child; walking 70 miles in sub-zero temperatures to get food; or packing up the family to fly from the North Pole to the South Pole, just for a few extra hours of daylight. All without a single road sign to get you there.

Such scenarios are common for the gray whale, the emperor penguin, and the Arctic tern, respectively-along with others in the animal kingdom, where migration has evolved over hundreds of thousands of years to enhance a species' chance of survival. Why do they migrate? And is the evolution behind these mass movements still at work, happening in our very parks, right before our very eyes?

In the Everglades and along the Carolina coast, Florida manatees are in the northernmost part of their range. When water temperatures drop below 68 degrees Fahrenheit, the manatee's thin layer of fat makes it hard to regulate body temperature, and a sluggish metabolism makes it harder to forage. So the gentle sea cow begins its leisurely migration in search of warmer waters.

That's when Everglades National Park becomes a fascinating place to observe migrating manatees. Following the "footsteps" of their ancestors, some head south to the park's Whitewater Bay. They move inland during cold weather, "bottom resting" in warm water layers trapped in the depths of basins, canals, and rivers. After the cold fronts pass, they bask in shallow bays that heat up rapidly when warm temperatures return.

Knowing precisely where manatees migrate is important to preserving their habitat, so the National Park Service recently partnered with the U.S. Geological Survey to track manatees with satellite transmitters. This information should bring conservationists closer to protecting an endangered species that wanders outside protective park boundaries.

Like the manatees, pronghorn know no borders. The antelope-like ungulates in Grand Teton make up the second largest migrating herd in the Western hemisphere, traveling about 150 miles twice a year. The park's high mountain meadows are perfect summering grounds, but harsh winters force the group into lower elevations, near the Red Desert.

Perhaps the greatest mystery about pronghorn migration is how to preserve it. Historically, at least eight routes existed for the pronghorn to travel today, only two corridors remain, and they are being squeezed tighter as housing developments spread across the region.

On a smaller scale, consider the green darner. This common dragonfly is known to migrate along Lake Superior, laying eggs in parks like Pictured Rocks National Lakeshore. But not all green darners migrate; and entomologists aren't sure why. Amy Maskey, acting entomologist at the park, has a hunch that migrating increases reproductive potential. Individuals traveling north extend their mating season, and their larvae develop faster than the resident larvae. Could this be evolution at work?

"The evolution of a migrant population would help ensure the survival of the species as a whole, by allowing them to retreat to a more favorable climate," Maskey says. "What I can't say, for sure, is which came first-the resident or the migrant. I don't know that the question has ever been addressed before."

Some migration rituals like that of the pronghorn have existed in this country for more than 6,000 years, making these ancient movements part of America's natural heritage. As humans continue to affect the land between parks, the protected areas within the parks provide refuge for weary travelers, whether they are resting, just passing through, or settling into their final destination.

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