WINGING INTO TAMPA BAY: Cast of Thousands Arriving Daily
by Mary Kelley Hoppe

This time of year, winter visitors numbering in the hundreds of thousands are descending on Tampa Bay, clamoring for a sunny spot on sugar-white sandy beaches. But there's no sense blaming these northerners for traffic congestion -unless you're winging it.

The great avian migration is underway. The rite of passage repeats itself each fall as flocks of migratory birds journey from breeding grounds in such faraway spots as Alaska, Canada and the Great Lakes to wintering grounds in Florida, Central and South America.

Bay area residents have a ringside seat at the show. And what a spectacle it is. "You wake up in the morning and if you get out early enough you can hear the faint noise of thrushes, bobolinks or warblers passing overhead," says Rich Paul, who along with his wife Ann watches over Audubon's Florida Coastal Islands Sanctuaries.

The action starts heating up long before fall casts its cooling spell on the summer weary. Piping plovers begin migrating in July, while ducks, loons and white pelicans arrive as late as early November.

Many migratory species spend six to nine months here, underscoring Tampa Bay's importance to birds and debunking the popular belief that so-called "wintering grounds" are secondary habitats.

The incredible journey

Consider the piping plover, a small shorebird that returns year after year to the same sandbars at Pinellas County's Fort DeSoto Park, Caladesi Island, Shell Key and Three Rooker Island. The weary visitors wing in from Canada, the Great Lakes, Massachusetts and North Carolina for some well-deserved rest and relaxation following breeding season.

Flocks of plovers begin arriving on beaches in July and stay until March when they return to their breeding grounds. Their long, narrow, sharply pointed wings are perfectly engineered for long distance flight. Plovers and their larger cousins, the killdeers, are characterized by relatively large eyes and short bills that are straight but slightly swollen at the tip, perfect for catching insects.

Along with piping plovers, birds wintering here include common loons, horned grebes, numerous ducks such as the lesser scaup and northern shoveler, long billed curlews, marbled godwits, sanderlings and least sandpipers, ruddy turnstones, and white pelicans.

The region also is host to a famous population of migratory whooping cranes. Each fall since 2001, new recruits have followed a surrogate parent - an ultra-light painted to look like mama - from Wisconsin to wintering grounds in the Chassahowitzka National Wildlife Refuge near Crystal River. The migratory route is imprinted in the young cranes after just one trip.

For others, like the red knot, Tampa Bay is but a brief pit stop for rest and refueling.

Shell Key is particularly well known for hosting large flocks of red knots, which forage on exposed mud flats, rebuilding fat stores to sustain them on their long journey south.

Few avian wanderers can match the epic journey of this diminutive sandpiper. Weighing in at a mere 4.7 ounces and no more than 9.5 inches long, the red knot breeds on the Arctic Circle above Hudson Bay and winters some 8,000 miles away in Argentina.

During their northward migration in the spring, red knots arrive in Delaware Bay in May after flying 7000 miles from Argentina. There, feasting on horseshoe crab eggs, they double their weight during a two- to three-week stay before flying another 1000 miles to their breeding grounds in Canada. An estimated 80% of the red knot's western hemispheric populations congregate on the Jersey shore at this time of year.

Shell Key and Three Rooker Island also are key stopover sites on the red knot's northern migration.

Commanding an impressive post on the opposite end of the size spectrum is the American white pelican, which soars into Tampa Bay each fall from Minnesota and North Dakota. Flocks of white pelicans congregate near Ybor City on Tampa's McKay Bay. Bigger than his familiar brown cousin, the white pelican has a nine-foot wingspan, the largest of any bird in North America except the California condor.

Flight tracking

Just how intense is the buzz on the airwaves this time of year?

"We've seen traffic rates of up to 250,000 birds over the course of an hour in the fall," says Dr. Sid Gauthreaux, director of Clemson University's Radar Ornithology Lab, with highest densities following southerly cold fronts favored by avian hitchhikers.

"That's a lot of birds moving South," adds Gauthreaux, "and what people see by day is just a tiny snippet of what takes place under cover of darkness."

Radar, originally developed to detect airborne targets such as aircraft and weather, is also a powerful tool for detecting the density, location, direction and speed of biological targets such as birds and bats. "Weather radars are designed to detect small droplets of rain," says Gauthreax. "Birds are like big droplets of water in the atmosphere."

Tapping into an extensive Doppler radar system covering the entire continental U.S., researchers are learning a lot about migratory patterns. Most small birds flying at night cruise between one and three thousand feet above ground. That puts them directly in the path of military aircraft flying at lower altitudes.

"There's a real problem with bird-aircraft collisions," Gauthreaux says. "That's why a lot of our support comes from the Department of Defense so we can provide them with crucial flight safety information."

"On the conservation side of the ledger, we've discovered that shortly after the birds take off they give us information about the habitats they've departed from." For a brief moment, as the birds ascend into the radar beam, their echoes indicate the locations of migratory stopover areas - areas that need to be protected if migrant birds are to survive.

Clemson also uses the national radar network to produce nightly maps of migratory movement so researchers can compare activity night to night and year after year to distill trends. "If you have a general decline, it will show up in these patterns," notes Gauthreaux.

Tailing the swallow-tailed kite

Closer to home, Gainesville researcher Ken Meyer is tracking the migratory path of the nation's largest population of swallow-tailed kites, with support from the Disney Wildlife Conservation Fund. The director of the Avian Research and Conservation Institute has been studying the raptors since 1988. "We had no idea where they spent the winter and how they got there," Meyer says.

Using tiny solar powered satellite transmitters attached to the birds with a shoulder harness, Meyer has documented the kite's annual pilgrimage from Florida and Georgia to less than a dozen cattle ranches in Brazil. "They gather in large night roosts in late July or early August, as many as 1500 to 2200 birds at its peak," says Meyer. "A single site near Lake Okeechobee attracts and helps prepare at least half of the U.S. population of kites," he adds.

The transmitters weigh 18 grams, or about three percent of the bird's weight. Some 44 birds have been fitted with transmitters over the past seven years, including nine this year.

After gathering in roosts, they gradually move down the Florida peninsula singly or in small groups of less than 25. They wait for a good tail wind, then jump offshore during the day. Once they've departed, the birds are committed to crossing the water, at least to Cuba and then to the Yucatan peninsula. From there, they follow the east coast of Central America into South America. Entering in Columbia, they cross the Andean mountain chain at its lowest and narrowest point, before heading southeast into Peru, Brazil, Bolivia and on to their final destination. A number of them come through Tampa Bay on their return.

But there is no guarantee they'll have tail winds the entire way, Meyer notes. "We have evidence that they are sometimes forced to stay up over the water for as long as three nights."

That's remarkable, says Meyer, because raptors (birds of prey) very rarely cross large expanses of water. The soaring birds rely on thermals produced by warm air rising over land.

Even more remarkable, adults leave the U.S. two to six weeks before their young, yet the offspring manage to arrive at the same spot some 5,000 miles away. "We tracked a son that left five weeks after his mother, traveled faster, and at one point was within 12 miles of her in Brazil," Meyer said. "It's very likely he found the group of birds that included his parents."

"We're identifying the places that education and conservation can have a dramatic effect on their survival. Just as important, we're identifying places that are undoubtedly critical to migratory birds in general -places ecologists call 'stopover sites' and concentrated 'passage points.' We can apply these results to conservation action in Brazil, but we're also working with Mexico and Belize."

In Florida, Audubon's Important Bird Areas Program has identified 100 critical sites for birds.

Why do they migrate?

Some species migrate south in the winter when food becomes scarce and conditions too harsh to support them at their breeding grounds. This is clearly true for insect-eating birds in Canada and the northern United States where the number of available insects plunge to almost zero, along with the temperature.

Less clear is why birds like the swallow-tailed kite, which lives in temperate zones, leaves its breeding grounds for a perilous and long journey south. Some birds appear to have a genetic drive to migrate controlled by an internal clock operating on annual rhythm. Each year, at a certain time, their biological clocks signal that it's time to migrate.

Of slightly more than 650 bird species in North America, an estimated 75% engage in some form of migration.