Science: Long Way from Home

Wandering through a Florida meadow in the spring of 1952, amateur Birdwatcher Richard Borden spotted a curious sight: among a grazing herd of cattle was a flock of yellow-legged, short-necked white herons, darting between the cows' legs, snaring grasshoppers flushed up from the pasture. Borden casually shot a series of pictures, mistaking the birds for snowy egrets, a common Florida species. Months later, Borden discovered he had the first pictures ever taken of a new U.S. immigrant: the Old World's buff-backed, yellow-billed cattle egret (Bubulcus ibis).

The egrets' migration to the Western Hemisphere is one of today's most fascinating ornithological puzzles. Never had a land bird migrated 3,000 miles across the ocean from Africa and settled successfully on the other side. The cattle egret is a strong flyer (30 m.p.h.) and a notorious wanderer. But most of its earlier nomadism had been confined to Africa and Europe, where it has been spotted among herds of cattle all the way from the British Isles to the Cape of Good Hope.

At first, ornithologists speculated that the birds had hitched a free passage on cattle boats to South America. Now the prevailing theory is that sometime around the turn of the century—when they were first sighted in the Guianas—a single flock of the birds, migrating from Senegal northward, was trapped in an easterly gale, blown off course clear across the Atlantic to the South American coast. The few hardy survivors nested, reproduced and moved north to the U.S. about 1941 in ever increasing numbers.

In its new environment, the cattle egret has flourished surprisingly well. Flocks of 200 to 300 can be seen in Puerto Rico; the bird is common in Haiti. Florida is experiencing an egret explosion: two years ago, Florida's cattle egret population was 5,000; today it exceeds 15,000, and the sociable birds have been spotted in every state along the Atlantic and the Gulf of Mexico. One wanderer, apparently lost, flew aboard a ship 200 miles off the coast of Newfoundland; another was shot by a farmer near Portland, Me. who complained it was upsetting his chickens. In the mud-and-mangroves Everglades National Park, where there are no cattle, the wily egrets trail tourists' cars, trapping insects stirred up by the moving tires.