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Birds' Life No Picnic

Tribune photo by Robert Burke

Terns nest in clusters near the shore of a protected island in Tampa Bay. Monitored by members of the National Audubon Society, the birds act as a group to ward off predators.

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By SUSAN M. GREEN

The Tampa Tribune

Published: May 31, 2008

RIVERVIEW - You see them scurrying along beaches, plucking tiny critters from the ebbing waves, or maybe begging for part of your picnic lunch.

The sights and sounds of shorebirds have long been a staple of the Florida beach-going experience. Avian census takers at Audubon of Florida say many of those feathered fixtures start life on the spoil islands of Hillsborough Bay.

But it's not easy, not from the get-go.

"They're always on the edge of death," said Ann Hodgson, Audubon's coastal island sanctuaries manager in Tampa Bay, as she checked last week on some shorebird families off the coastline of Riverview and Gibsonton.

Take the downy gray American oystercatcher chick spotted on a Tampa Port Authority spoil island called 2-D. Cautiously, the fledgling stepped into the spot where the waves lapped the sand and began studying the bay bottom.

"He's learning how to eat little marine worms and crustaceans on the edge of the shoreline," Hodgson said, peering at the scene through binoculars.

The chick was not old enough to fly. An adult oystercatcher paced the beach close by. Several yards away, another adult stalked the shoreline, chirping loudly.

"He's telling the chick right now it might have to run for cover," Hodgson said.

High up in an Australian pine perched a fish crow, one of the prime predators of baby oystercatchers on the spoil islands.

With approximately 80 nesting pairs, Hillsborough Bay is credited with producing about 15 percent of the state's American oystercatchers, a species that is listed on Audubon and government lists as in danger of extinction because of declining numbers.

That Junior Oystercatcher made it to the age of 4 or 5 weeks is a credit to the parent birds, Hodgson said. Storm surges, predators and human intrusion take their toll on dozens of Hillsborough Bay nests every year. Whether Junior can survive long enough to take on the sleek black and white coloring and bright red bill of an adult is iffy at best.

The nesting season in Hillsborough Bay generally runs from March to July. Some birds with nests that fail will try again late in the season, Hodgson said.

"Hillsborough Bay is actually very important" to the perpetuation of coastal birds, Hodgson said. Besides the beach-nesters, birds such as roseate spoonbills, reddish egrets, brown pelicans and ibis raise offspring on mangrove islands in Hillsborough Bay.

According to the Audubon of Florida Web site, up to half of the estimated 50,000 breeding pairs of colonial water birds in the Tampa Bay area choose Hillsborough Bay for their nests.

Some species, including terns, nest in clusters on shorelines and act as a group to ward off would-be predators. Hodgson pointed out a colony of Royal and Caspian terns on the port's island 3-D during an Audubon patrol last week. Adults in the group pointed their beaks to the skies when they saw a predator bird flying overhead, presenting the appearance of a big pincushion.

"See how they all put their bills up?" Hodgson asked. "That's one of their defense mechanisms. ... If they think there's a threat from up above, it's like a little forest of orange toothpicks."

Oystercatchers - along with terns, laughing gulls, plovers and black skimmers - scrape out depressions in the sand, shell or rock for their nests and depend largely on camouflage for protection.

"One of the adults always acts as a sentinel bird on the shoreline," Hodgson said, "and the other adult has incubation duty."

Male and female oystercatchers take turns incubating their eggs, foraging for food and feeding their hatchlings and watching out for predators.

People have largely taken over many of the beaches favored by nesting shorebirds. Spoil islands, created from the material dredged to deepen or widen shipping channels, have provided a substitute. The port authority, which owns the islands, periodically installs berms that buffer the waves and tries to manage the habitat to increase the likelihood of nesting success.

Most of the islands in Hillsborough Bay are off-limits to people and posted with no-trespassing signs. Even so, human intrusion takes its toll on nests each year when people ignore the signs and land on beaches during nesting season, Audubon wardens say.

"The entire shoreline is posted, but people sometimes don't realize that means no trespassing on the beach," Hodgson said, noting that signs must be placed above the high-water mark to keep them from being washed away. The only Hillsborough Bay islands open to people are Fantasy Island and Beer Can Island.

Boaters who care about future populations of shorebirds will stay 30 to 40 yards off the shoreline to avoid flushing adult birds, Hodgson said. If the parent birds desert their nests, even for a short time, their offspring become vulnerable to the sun's intense heat or predators.

AMERICAN OYSTERCATCHER

A look at one of the endangered birds that nest in the Tampa Bay area.

APPEARANCE: Adult birds sport dark brown, black and white plumage and a bright red bill.

HABITAT: Needs sandbars or mudflats for feeding and shell-covered beaches for nesting.

DIET: Oystercatchers use their powerful bills to pry open mollusks and also eat marine worms and crustaceans.

POPULATION: The National Audubon Society estimates 7,200 oystercatchers live in North America. The Florida Fish and Wildlife Conservation Commission estimates 1,000 birds breed in Florida. An unknown number spend winters in the state.

LISTINGS: Considered a species of special concern by the Florida Fish and Wildlife Commission, the American oystercatcher also was on the 2007 Audubon "watch list" of birds in decline, mostly because of diminished habitat. The U.S. Shorebird Conservation Plan designates the bird as a "species of high concern."

Sources: The National Audubon Society and Florida Fish and Wildlife Conservation Commission

Reporter Susan M. Green can be reached at (813) 865-1566 or sgreen@tampatrib.com.

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