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Page 2/2 - Posted February 26, 2010
Giant petrels finding unique breeding success near Palmer Station
This season there are 27 nests on Humble to visit. While it’s been six years since Patterson-Fraser has been in the field — she’s remained at home in Montana to fledge her own “chick,” as she puts it — she moves confidently among her old friends.
Some parents greet her with a bird bark, but as she leans in and reaches underneath their warm underbelly to pull out a plump chick, they merely nuzzle her arm with their razor-sharp beak, instinctively trying to nudge her into the nest as one of their own brood.
“We have this very kickback, very mellow, subpopulation out here,” she says. On the other Palmer area islands — such as Stepping Stones, a grass-covered islet with a high density of giant petrels — the birds are not habituated and so more skittish. The birders limit their work mainly to taking a census of the nests and banding the chicks, sometimes climbing short but steep, shale cliffs to do so.
Photo Credit: Peter Rejcek
A transmitter on the back of a giant petrel tracks its foraging pattern over hundreds of kilometers.
But the Humble giant petrels are mild enough to allow the birders to put small transmitters on their backs to track their movements during the breeding season. Some birds make long-distance hauls of more than 1,000 kilometers over a couple of weeks to hunt for food.
She and Yeager hope to outfit two Humble birds today with the GPS transmitters. It’s something of a subjective judgment call, trying to feel which bird will be least ruffled by the device, which stays on its back for up to a couple of weeks. It’s also an economic decision — the GPS transmitters cost $4,000 a pop.
“Not every one of them wants jewelry either,” Patterson-Fraser says of the boxy instruments, which sport a long antenna that extends toward the bird’s tail.
The operations are fast and painless for the bird. Patterson-Fraser makes her normal approach, half-singing random rhymes and promising the bird squid popsicles if he will cooperate. She carefully pulls out a sleepy chick, which another team member holds, while she slips a wooden egg underneath the bird to placate its brooding instinct. She works quickly to fasten the transmitter with waterproof tape and a couple of zip ties.
In the last 10 years, the team has made about 275 transmitter deployments on giant petrels. “We’re the only program that’s been able to do that,” Patterson-Fraser says.
Except for work done by British ornithologist Steven Hunter, in the 1970s and 1980s, this is the only major giant petrel study under way, she adds.
“No one else … has the data we do on breeding biology and foraging ecology, which because of its very long-term nature, now provides us with the opportunity to address specific hypotheses. This is the next phase of this study,” says Bill Fraser via e-mail.
What are they learning?
First, the birds are doing better than Adélies in this region. Their nests have tripled from more than 200 to 600 in the last 30 years, while Adélie breeding pairs have dropped from 15,000 to 2,500.
“My theory is that their flexibility as predator-scavengers is what allows them to do as well as they do around Palmer,” Patterson-Fraser explains. Many of the nests contain recent snacks to illustrate her point, from partially munched penguin legs to bits of squid and fish. Adélies subsist mainly on krill, which are also sea ice-dependent, and fish when they can find them.
Fraser says his team believes that the success of the giant petrels may be coming at the expense of the Adélies, particularly fledgling penguins taking to the sea for the first time in February.
“We are starting to suspect that their effects … on the population may actually be quite substantial, and probably now constitutes a serious additional population stressor,” he says.
Still, the Palmer region may be the exception to the rule for giant petrel success, Patterson-Fraser notes. In other areas, the birds are declining. They’re extremely susceptible to human disturbances, such as aerial over-flights and physical destruction of habitat, and changes in weather patterns, particularly to winds and precipitation.
“We’re finding more fishhooks,” she adds. Indeed, during the team’s couple of hours on Humble, they find a rusty fishhook near a nest. Patterson-Fraser logs the find in her notebook, which contains a byzantine code to the layman that tracks chick weight and beak length, along with notes about behavior and other finds.
“This was not something that I had envisioned doing for my whole life, but that’s how it’s looking,” she says, skipping across the rocks to the next nest. “It’s a lot of work, but it’s worth it.”