Seabird sales pitch: for seabirds starting their first family, home is where biologists fake it.
Late at night on a tropical island in the Pacific, an eerie clamor rises from an old volcanic crater.
Drawn by the sound, visitors from the sky soon arrive -- graceful, gull-like seabirds, coursing through the misty equatorial air. They descend and disappear into a dripping forest of ferns and evergreen shrubs.
Which is just as ornithologists Richard H. Podolsky and Stephen W. Kress have planned. Beneath the green canopy, the birds find ready-made nesting burrows in the volcanic ash -- the kind of burrows these dark-rumped petrels might excavate for themselves. As they waddle about, inspecting the burrows, some pass right beneath a loudspeaker blaring the recorded calls of a teeming colony of petrels. At dawn, the noise stops and the last petrels head back out to sea.
But they will return. For 62 nights each summer on the Galapagos island of Santa Cruz, the two ornithologists hold open house for nutially motivated petrels. Although scientists by profession, Podolsky and Kress are also salesmen of sorts -- salesmen of seabird real estate. Using recorded bird calls, model decoys and artificial burrows, they mimic the sights and sounds of thriving seabird colonies. By luring their avian customers to these realistic sets, they try to breathe life back into ailing island ecosytems that once rang with the racket of nesting seabirds.
"BAsically, we try to influence the nestsite selection of prebreeders," says Podolsky, director of scince and research at the Island Institute, a nonprofit ecology research organization in Rockland, Maine.
Compared with most inland birds, oceanic birds wait a long time before breeding -- from four to five years for puffins to as many as 10 years for the gigantic albatrosses, explains Podolsky. "These prebreeders are what we call prospectors," he says. "Prospectors wander widely, cruising to lots of different areas, and they either settle near their natal site or somewhere on an island nearby."
But not just any island will do. In the discriminating eyes of a prospecting seabird, an attractive island usually means one with an established, growing colony of the same species. Healthy colonies offer protection against predators, better chances to meet mates, and perhaps even a source of information for finding food, says Kress, who works with the National Audubon Society in Ithaca, N.Y. So it behooves the inexperienced prospector to choose a "good" colony -- one not too thinly or thickly settled, and one exuding a particularly confident tone of chatter.
With their various props and sound effects, Podolsky and Kress try to duplicate the prospector's dream neighborhood. Though they have yet to decipher the individual calls that form the din of a vigorous seabird colony, Kress says, "the basic message we think we're sending to a young bird looking for a place to nest is, 'Ah, this is a good place, because there are many other birds here,'"
For centuries, that message resounded from Eastern Egg Rock, a treeless, granite island off the coast of Maine. Thousands of terns -- sleek and nimble little aerialists that hover and plunge headfirst after fish -- and other seabirds gathered there each summer in noisy masses. But the late 1800s brought an era of feather-hatted fashions, transforming the Eastern Egg seabirds into human hood ornaments. Although the 1916 Migratory Bird Treaty Act finally checked the milliners' annual slaughter, aggressive gulls soon filled the island's void, forcing wandering terns looking for a friendly neighborhood to search elsewhere.
In 1978, following a federally assisted gull-eradication campaign on Eastern Egg Rock and nearby islands, Kress saw a break for the terns' return.
For the next two summers, terns flying over Eastern Egg Rock looked down on a "colony" of 33 wooden terns -- some standing alert, others apparently incubating -- from whose midst arose the recorded racket of a typical tern gathering. Nearly every day, terns hovered and then settled down among the new colony. Some pecked and bluffed menacingly at their stiff rivals; some courted the more appealing models, offering gifts of fish and even mounting the coy seductresses. Gull and human intruders were hurried off by the little bombardiers.
Within five years of the phony colony's first beckoning, Eastern Egg Rock bustled with 1,000 pairs of nesting terns. Though an avian cholera epidemic decimated the population in 1984, the terns have since rebounded, reaching 1,232 pairs this summer.
Since that initial success, Kress and Podolsky have experimented with sound and sight lures to attract other prospecting seabirds -- ranging from Atlantic puffins and robin-sized Leache's storm petrels in the Gulf of Maine to Laysan albatrosses with 7-foot wing-spans spaHawaii.
Their latest prospect lives on the Galapagos Islands, 600 miles off the coast of Ecuador. The dark-rumped petrel -- known locally as pata pegada, or web-footed an -- is an oceanic bird whose arm-length nesting burrows once pocked the islands' humid volcanic highlands. For perhaps a million years or more, petrels had nested there in relative safety, free from mammalian predators.
But along with settlers in the last 60 years came pigs, horses, burros, cattle, goats, dogs, cats, and rats -- ecological additions the petrels were unprepared to handle. The cows and horses trampled burrows; the dogs, cats and rats ate birds and eggs; and the pigs efficiently did both. "During the [petrel] breeding season," says Kress, "the locals couldn't even eat the pigs because their flesh smelled so much like petrels."
Surviving petrels retreated to the islands' steepest, most rugged and most inaccessible canyons, where even pigs feared to tread. But cats and rats were not so easily eluded, and the petrel population continued to plummet. Rough population estimates in the mid-1980s revealed a 30 percent yearly decline of the Galapagos petrels -- and a grim 10- to 15-year countdown to extinction.
With biologists from Ecuador's Galapagos National Park and the Charles Darwin Research Station on Santa Cruz Island, Podolsky and Kress set out to help the dark-rumped petrels. They planned to lure petrels to dense colonies of artificial burrows, where wildlife managers could guard them against predators. On Santa Cruz Island, a volcanic crater lush with evergreen Miconia shrubs provided the perfect test habitat.
The crew's work began in 1988 with a sound rest not far from the crater rim. From 10 p.m to 6 a.m, June to early August, biologists randomly broadcast half-hour recordings of different petrel calls under 40-foot-tall "mist" nets. Birds dropping by to investigate would fly into the soft, nearly invisible nets, where biologists stood by to examine and band them.
To no one's great surprise, the more aggressive calls and the periods of silence lured relatively few petrels. But when the calls of a contented colony piped up, the researchers found themselves plucking petrels from the nets at twice the normal rate. And when beckoned by the recording of a colony taped over itself to double its intensity, petrels hit the nets three to four times more often than during silent periods.
But the more-the-merrier concept had its limits: Triple-intensity recordings drew fewer petrels than the double-intensity calls.
Once the petrels had voted for their favorite tune, the researchers took the recording to the crater -- where they had dug several "colonies" of 20 artificial burrows beneath the Miconia canopy -- to begin luring tenants. Each colony encircled a speaker playing the double-intensity sounds. By loosely lining burrow entrances with toothpicks (to detect any visitors brushing past) and by looking closely each morning for footprints, feathers and droppings, the observers kept a running tally on each burrow's nightly occupants.
"Right away we started luring birds," says Podolsky, "but most didn't stay long. The birds just kind of nipped in, spent a few hours, . . . and were gone by the morning."
By the end of the 1988 field season, however, petrels were not only investigating burrows by night, but moving in for a day or two at a time, he says.
If that had been the sole accomplishment of the 1988 season, Podolsky and Kress would have considered it a success. The petrels they had netted during the sound tests revealed that most of those investigating the colony were young prospectors, not yet old enough to lay eggs. Their mere interest in the artificial colonies hinted they would someday return with more serious intentions.
Yet some, it turned out, had come better prepared. The following year, as two crew members began checking the artificial burrows to start the new field season, a handful of soil from deep within burrow D-17 came up speckled with telltale white fragments. Sometime late in the '88 season, unbeknownst to the observers, a dark-rumped petrel had laid an egg.
The team repeated the experiment in '89 and '90, adding a total of 140 artificial burrows. Each year, the number of night visitors increased, and more of them lingered through the day. Podolsky and crew found birds sitting in burrows during morning checks in 1989, with burrow D-17 again housing incubating petrels. This summer, the number of nesting petrels tentatively stands at one pair. With the verdict still out on some suspiciously busy burrows, Podolsky is optimistic that the count will rise before the birds head out to sea in a few months for the winter.
At the suggestion that a handful of petrel nests seems a modest return for 220 hand-dug burrows and three seasons of avian advertising blitzes, Podolsky smiles like a salesman about to close a million-dollar deal. For he knows the nature of his customers.
The dark-rumped petrel often lives into its 30s and takes eight years to mature--an unusually long time for a bird of its size. "When we play our recordings, we don't appear to lure in breeders, we appear to only lure in young prospectors," Podolsky says. "We think they start returning to the island at 2 years old and continue to prospect until they're 8 years old." That leaves a comforting window of time before the return on his investment comes due. And in light of the finding that young petrels have already perused more than 70 percent of the 220 artificial burrows, the prospect of a petrel boomtown becomes easier to envision.
Podolsky and Kress see an expanding global need for their services, and they may be the world's only salesmen to view a rising demand as sad news. Dark-rumped petrels of the Galapagos and Hawaiian islands face a continuing threat from expanding agriculture and introduced predators, they say. And seabird situations around the world look similarly griM. Of the approximate 270 species of seabirds worldwide, 30 are listed as endangered or threatened.
"Ultimately, our responsibility as biologists is to maintain the biological richness, the natural heritage of this planet," says Podolsky. "It's like the rivet puller analogy by [ecologist] Paul Ehrlich: You start pulling rivets from an airplane and nothing seems to happen. But there comes a point. . . ."
For now, most of the ornithologists' efforts are mere stopgaps, helping to settle and protect new colonies of endangered seabirds until less predator-infested island homes can be found. For some birds, however, the menaces aren't limited to rats, gulls, pigs and people.
Consider the short-tailed albatross. All but seven of the last 100 or so breeding pairs nest on Tori Shima Island off Japan. "The idea is to lure tham to the other side of the island," says Podolsky. In the meantime, the heart of the short-tailed albatross population innocently gathers each fall to lay its precious eggs in the shadow of an active volcano.
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|Title Annotation:||ornithologists' attempts to lure birds back to former island nesting sites|
|Article Type:||Cover Story|
|Date:||Sep 1, 1990|
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