Awash in warblers, noddies on the Dry Tortugas : It’s birder nirvana when more than 290 migrating species briefly alight at this national park.

DRY TORTUGAS NATIONAL PARK, Fla. —  As the red-brick walls of Ft. Jefferson take shape through the misty dawn, those passengers able to shake off seasickness grope their way to the yacht’s deck and note that the day promises to be bird-watching perfect: rain in squalls, gusty winds, unrelieved gloom.

Then, binoculars raised, the birders begin to call roll.

“Magnificent frigate bird!”

“Sooty tern!”

“Double-crested cormorant!”

During most of the year, the seven sand-spit islands of the Dry Tortugas are easily one of the most peaceful, least-visited national parks in the United States. Situated in the Gulf of Mexico almost 70 miles from Key West, Fla., these tiny, barren isles are not easy for visitors to get to--and offer no amenities when they get there.

In 1995, according to the National Park Service, the Dry Tortugas attracted fewer than 33,000 visitors--about what Yosemite or Yellowstone draw on an average summer weekend.

But there is a two-month busy season in the Dry Tortugas, when tens of thousands of birds show up and hundreds of avid bird watchers show up to see them. Some birders fly in for the day on small pontoon planes. Others arrive on charter boats. “On any given day in April or May, this can be the best place in the U.S. for seeing migrating birds,” said Wes Biggs, a first-class birder and tour guide who often has counted more than 100 species of birds in a day on the Dry Tortugas.

Indeed, on a routine, sunny day in spring, the parade grounds of long-abandoned Ft. Jefferson on Garden Key, as well as the woodsy wilds of nearby Loggerhead Key, are alive in an avian kaleidoscope of color as migrants forage for insects and seeds that will fuel their flight north. Warblers, flycatchers, swallows, vireos, tanagers and sparrows are everywhere on the ground and in the trees, while 100,000 sooty terns and 2,500 brown noddies keep up a whirling commotion over their rookery on Bush Key.

For hard-core birders building a life list--a personal record of each species of bird sighted--the Dry Tortugas are a mecca. These islands are the only North American breeding ground of the masked booby, sooty tern, the brown noddy and the magnificent frigate bird.

And for migrating birds making the annual journey from Central America and South America to the United States and Canada, the Dry Tortugas are a last-chance oasis, a flyway rest stop too inviting to pass up. When bad weather causes what are known as “major fallouts” of feathered transients, the birding is even better. The checklist of birds seen in the Dry Tortugas exceeds 290 species.

One of the first to notice the abundant bird life here was Juan Ponce de Leon, the Spanish explorer who in 1513 named the islands Las Tortugas after the many turtles he saw. The reefs were later called “dry” on mariners’ charts to indicate there was no fresh water.

The first serious birder to call was John James Audubon, who visited what he called “these inhospitable isles” in 1832. About the same time, the U.S. government decided to fortify the islands as a way of protecting ships traveling from the Mississippi River to the Atlantic.

Construction of Ft. Jefferson began in 1846, and continued for 30 years but was never completed. During the Civil War, the three-decked fort served as a Union military prison for deserters and was used to hold four men charged of complicity in the murder of President Lincoln. Among the four was Dr. Samuel A. Mudd, who set the broken leg of assassin John Wilkes Booth.

The Army abandoned Ft. Jefferson in 1874, and in 1908 the area was made a federal wildlife refuge to protect the sooty tern rookery from egg collectors. The fort was named a national monument in 1935.

Since being designated a national park in 1992, the number of visitors to the Dry Tortugas has increased steadily, says park manager Wayne Landrum, one of 10 federal employees who lives here full time. Still, the park remains relatively inaccessible. The only way to get to the islands is by boat or seaplane from Key West. But even that access is down, at least temporarily, after two recent plane crashes grounded one charter company.

Nor are there any overnight accommodations, food or much drinking water. There is a primitive campground on Garden Key outside the fort, and one toilet on the dock.

For Biggs, 47, who guides birders to the islands through his Orlando-based Florida Nature Tours and was even married here in 1988, the islands are “the perfect place to be.”

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“Why? Because this place combines the best of human and natural history. There are no cars, no noise--it’s extremely peaceful; you’ve got a huge variety of land and sea birds, the architectural wonder of the biggest masonry fort in the Western Hemisphere, the history of Dr. Mudd. . . .

“As far as I’m concerned,” says Biggs, peering through his binoculars at a brilliant hooded warbler on the ground just feet away, “this is paradise.”