Why researchers are in a hurry to learn the many secrets of the Magnificent Frigatebird
By Mark Hedden | Published: 12/1/2013
The Magnificent Frigatebird is a mysterious creature.
In flight, it tends to hang there, alone and aloof in an otherwise empty sky, floating on skinny, black, sharply angled wings. Occasionally, it can look as if the letter M had escaped from a forgotten gothic typeface and placed itself in the middle of a blank page.
It is a bird that makes you stop and stare.
The species has historically been a resident of the Florida Keys, yet for the longest time no one knew where it nested.
John James Audubon claimed to have shot a nesting frigatebird when he explored the Keys in 1832, although it was later believed that he actually shot a roosting bird sitting on an abandoned pelican nest, as frigatebirds sometimes do.
Nobody else recorded a nesting frigatebird until 1969, when Alexander “Sandy” Sprunt and John Ogden, two notable Florida ornithologists, came upon a colony of about 100 nests at the Marquesas Keys, an uninhabited tangle of mangrove islands 20 miles west of Key West. It was the only colony in North America, and as soon as it was discovered, ornithologists started charting its decline.
Tom Wilmers, a wildlife biologist with the U.S. Fish and Wildlife Service who works in the Key West National Wildlife Refuge, where the colony was located, saw the nesting birds when he came on the job in 1984. “I just thought that colony would be there forever,” he said.
But by 1989 the colony at the Marquesas had been abandoned.
“It’s kind of haunting,” said Wilmers, who has worked regularly in the area in the decades since. “I miss them a lot.”
The frigatebirds established a new colony the following year, but it was smaller and 50 miles farther west at the Dry Tortugas, at the farthest edge of what can be considered North America. The next stop is either 90 miles south to Cuba or 400 miles southwest to the Yucatán Peninsula, in southeastern Mexico.
Magnificent Frigatebird breeds on scattered islands in the eastern Pacific from the northern Gulf of California to the Galápagos, and in the Atlantic from the Dry Tortugas south across the Caribbean and along the west edge of Central and South America from the Yucatán to Brazil.
The Florida Keys, the southernmost region in the continental United States, is the northernmost edge of the frigatebird’s Caribbean range, and it is not hard to see a member of the species there. Stand for 20 minutes anywhere you can see enough horizon and one will surely drift by, circling slowly on the thermals.
Frigatebirds get exponentially less common as you travel north up the Gulf and Atlantic coasts. They are light birds (less than a pound) with an expansive wingspan (seven feet across), and they sometimes get pushed around the continent by winds and atmospheric pressures ahead of big storms. Consequently, they are occasionally spotted in New Mexico, Colorado, Ontario, and other landlocked places (hence one of their old names, the Hurricane Bird).
Learn more about frigatebirds
Read more about the ARCI satellite-tracking project and find a link to tracking maps.
One bird’s movements
See a map of a female frigatebird’s travels between Florida and Mexico.
Sounds of a colony
Listen to the sound of bills and calls recorded at a colony of 5,000 frigatebirds.
The thing you eventually notice about frigatebirds, though, is that, while they are always around, they are never close. Usually they are a few hundred feet up, or perched on a channel marker or mangrove island a few hundred yards away. They keep their distance.
That distance adds to the species’ intrigue, but translated into conservation terms, it means the birds are vulnerable to disturbance.
In Audubon’s era, few people could travel in the shallow-water backcountry of the Florida Keys. But in modern times, kayaks, shallow-draft powerboats, Jet Skis, and paddleboards allow access to the area’s waters.
Many observers point to human disturbance as the probable reason the Marquesas colony collapsed. Wilmers remembers a tour-boat company that relied on the birds to drum up business. It distributed a promotional brochure that said, “Visit Frigate Island!”
While Magnificent Frigatebirds no longer nest in the backcountry of the Florida Keys, they do still roost there. In the summer, up to 7,000 are thought to be in the island chain and along the edges of the mainland. And those roosts are vulnerable, even to inadvertent disturbances.
“Frigatebirds look like pterodactyls. They are attractive, spectacular birds. Anyone who has a modicum of interest is going to be drawn to them, because they stand out,” Wilmers said. But when people get too close, “they often don’t even realize when they’ve caused a problem.”
At least not until the frigatebird has unfolded its long wings, worked laboriously to gain purchase on the air, and flown away.
“There are so many islands in the [backcountry] but so few that the birds choose to nest on,” Wilmers said. “They are very loyal to their roosts. They are not randomly selective at all. To them, all islands are not created equal.”
Roosts vary from 20 birds to more than 200. Roosts with over 200 frigatebirds are referred to as super roosts, and there are three known super roosts, all within two and a half miles of each other.
“You realize how special these roosts and super roosts are, and it is upsetting how vulnerable they are,” Wilmers said.
The disappearance of the colony at the Marquesas was not an isolated incident. About half of all Magnificent Frigatebird colonies in the Caribbean have been extirpated in recent decades. Part of this may be attributed to climate change and the increased difficulty of finding suitable, accessible food supplies. But part of it is the result of the human encroachment on the birds’ nesting and roosting habitats.
In the Florida Keys, most of the birds’ terrestrial habitat is under federal management, either by the Fish and Wildlife Service or by the National Park Service, so the best way to address the issue is through a management plan for the species. But a management plan requires data, and when a species has remained inscrutable, with so many aspects of its behavior undiscovered, for so long, data are hard to come by.
What we know about Magnificent Frigatebirds is largely the result of observations made at single locations, or from behavior witnessed by happenstance. It is known, for example, that, while they are pelagic birds, they cannot swim or get significantly wet; that in the interest of lightness and an enhanced capability to soar, their feathers contain no water-repellent oils; and that if the feathers absorb too much water, the birds drown.
It is known that frigatebirds feed primarily while flying, using their long, hooked bills to snatch fish or squid from the first few inches of the ocean’s surface. We also know that they sometimes practice kleptoparasitism. That is, they chase gulls, terns, and other, smaller birds, haranguing and abusing them until the pursued birds regurgitate the contents of their crop in mid-air. The frigatebirds then swoop in to snag the regurgitated items, usually partially digested fish, before they hit the water.
It is known that Magnificent Frigatebirds don’t breed until they are six or seven years old and that the females lay one egg per cycle.
It is known that the male shares the duties of incubation and feeding for the first six months, before moving on, and that the female spends up to a year and a half raising each of their young, meaning males can breed every year, females every other year.
It is also known that the mortality rate for offspring can be close to 50 percent, and that raising their young to maturity is a more costly endeavor for frigatebirds than for most birds.
What is not known are the frigatebirds’ daily and migratory habits. How far do the birds range from where they hatch? How important are particular roosting spots? How loyal are individual birds to those roosting spots? And just what does a frigatebird do when it drifts out of sight?
The best way to answer these questions, Wilmers and the Fish and Wildlife Service concluded, is through satellite tracking. To get started, they enlisted the help of the Avian Research and Conservation Institute (ARCI), a Gainesville-based nonprofit research organization that specializes in radio and satellite tracking Florida avifauna.
The 20-gram transmitters used for frigatebirds are solar-powered, provide up to five years of data, and cost approximately $5,000 each. Orbiting satellites retrieve the transmissions and redirect them to reception stations on land. Retrieving the data costs about $1,200 per year per transmitter.
With grants from the Fish and Wildlife Service, as well as additional money from the Florida Keys Audubon Society and the Hernando Audubon Society, the researchers acquired satellite transmitters for five birds in the Key West National Wildlife Refuge, and two more for additional birds from the Dry Tortugas colony. (The National Park Service provided in-kind and collaborative support on the project.)
High-tech tracking tools
Gina Kent, the ARCI research ecologist and coordinator who led the team in the Keys, had worked on other projects that involved tracking the movements of Swallow-tailed Kites, Short-tailed Hawks, Reddish Egrets, Wood Storks, and White-crowned Pigeons.
Photos of frigatebirds
The tools she used were high-tech, but her first problem was old-school: How do you catch a frigatebird? More to the point, how do you catch a frigatebird in a way that does not harm the bird in any way?
Kent and her crew, which included field techs Marjesca Brown and Steve Alsup, tried several configurations of mist-nets: setting them up high and erecting them low and at varying distance from the roosts. They tried baiting them with fish and leaving them un-baited — all with no result. They even considered a butterfly-style net on a long pole but rejected the idea.
Finally, they developed a sort of frigatebird thai chi — a series of non-threatening maneuvers that, if performed at the right time of day, allowed them not only to sidle up next to a frigatebird without flushing it but to grab it by hand.
Handling the bird was a two-person operation. One technician would hold the wings close to the body, so the bird wouldn’t hurt itself, and at the same time try to control the bird’s bill. “They are serious biters,” said Kent, who had frigatebirds chomp her hands and shoulders several times during the project. “They’ve got some pretty scrappy bills, and they will bite and they will fight.”
The second person would attach the transmitter with a Kevlar strap across the rump, a position that would keep the solar-charging panel exposed when the bird was flying but would not interfere with its day-to-day activities.
Kent said that, while holding a frigatebird, it was the vestigial feet that surprised her the most. “Their feet are so weird. They are the weirdest things I’ve ever seen. They’ve got two toes that look almost like an iguana foot,” she said.
Two data transmissions per day
In October 2012, Kent’s team caught and released one male and four females from the Florida Keys backcountry roosts. In May 2013, they caught and released a male and a female from the Dry Tortugas colony.
As soon as the transmitters were attached, the researchers started to receive two GPS data transmissions per day from each of the birds. The data opened a window into a previously unseen world.
All five birds trapped at the Florida Keys roosts left the area within the month, traveling south to Cuba and southwest to the Yucatán.
One female went to the Yucatán, then almost immediately flew to Cuba, returned north to the Florida Keys, and then traveled back to the Yucatán, all within about three weeks.
“They even fly at night,” Kent said. “They just move when the wind is right. There was a bird in Mexico that would leave the Yucatán and go on a foraging binge for four to seven days.”
All but one of the birds returned to the Florida Keys, and to the same roosts, by the spring of 2013. The exception was a female that disappeared off the coast of Nicaragua within a month of being released.
The male and female from the Dry Tortugas had a three- to four-week-old chick on the nest when they were captured. The male stayed in the immediate area for a few weeks. Then, after migrating toward the Florida Keys backcountry roosts for several weeks, it traveled 300 miles up Florida’s Gulf coast to one of the northernmost Magnificent Frigatebird roosts, near Cedar Key, a cluster of islands north of Tampa. The female, meanwhile, stayed in the area, never straying more than 60 miles from the colony, no doubt tending her offspring.
The data collection will continue for several more years. The birds’ locations and the history of their travels are updated daily on the ARCI website.
The hope is that solving a few of the Magnificent Frigatebird’s mysteries might bring about a way to protect them.
Mark Hedden is a writer and birding guide in Key West. He blogs occasionally at www.boneisland.com.
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