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Birds of a feather

Researcher finds special bond — and discoveries — among giant petrels

 

Donna Patterson-Fraser moves swiftly across the rocks on Humble Island, deftly leaping from stone to stone to avoid damaging the fragile moss that forms a threadbare carpet across the island and between the giant petrel nests along her route.

She and fellow field team member Kirstie Yeager also must weave around the small colonies of Adélie penguins — packed into irregular circles where the ground is stained light pink with guano — and the muddy wallows created by elephant seals. To call their combined smell “pungent” falls far short of the reality. It’s as if everything at a seafood market has turned strongly rancid.

But Patterson-Fraser and Yeager quickly pass the animals, hardly wrinkling their noses at the birds or the ill-tempered seals, the latter throwing their weight around to steal penguin territory.

One monstrously big seal barks and jiggles dangerously close to a colony. Weighing up to three tons, a bull can easily flatten a colony’s fragile chicks, even though some now stand nearly as tall as their parents do. Patterson-Fraser pauses long enough to curse the bully, as one feisty Adélie brays and jabs its beak at the trespasser, actually forcing the elephant seal to retreat.

“The Adélies have a tough enough time already. Now they have to deal with that,” says Patterson-Fraser, referring to the growing population of elephant seals on Humble. A changing climate along the northern tip of the Antarctic Peninsula has sent the local Adélie population into a steep decline over the last several decades as sea ice, a key habitat, has significantly retreated in duration.

But that’s not the story Patterson-Fraser and Yeager are interested in today. They’re on Humble Island to weigh and measure the snowy white chicks of southern giant petrels.

It’s a job that members of Bill Fraser’s field teams have been doing for more than 15 years now. Fraser is the principal investigator for the seabird component of the Palmer Long Term Ecological Research (PAL LTER) program, a mostly ship-based ecosystem study across a 700-kilometer swath on the western side of the Antarctic Peninsula.

The “birders” spend most of their energy tracking the bird populations close to Palmer Station on some 20 different islands, though some work is done farther south off the U.S. Antarctic Program’s research vessel, the ARSV Laurence M. Gould. The ship supports the LTER cruise every January, while the birders island-hop for their annual seabird census from October to March on inflatable rubber Zodiac boats.

In the early 1990s, Fraser’s work had focused on the penguins and a few other seabirds, like the intelligent and long-lived brown and south polar skuas. Patterson-Fraser wondered why he didn’t also work with the giant petrels.

“There’s got to be a story here,” she recalls telling Fraser, whom she started working for during the 1991-92 summer field season.

But the birds had a reputation as being difficult to handle. They “gaked” — a vile, oily stream of stomach contents — to defend against enemies. They’ll gak on you, Fraser warned her, but gave her the go-ahead to try.

The warning didn’t deter Patterson-Fraser, a short but energetic woman with a pale complexion burnished bright red by wind. She picked out a loop of nests that she watched for an entire season — basically becoming acquainted with the birds.

“You’ve got to take the time to watch and learn the signals,” she says. “They’re easier than people. I’m not a people person. I’m animal person. … You don’t have to second-guess what they’re thinking, because they’re straight up with you. And you never worry about them talking smack after you left; they’ll just talk smack right to your face.”

After making protracted introductions that first season, Patterson-Fraser then proposed the team start tracking the growth of the chicks as a way to assess the parents’ ability to care and raise them to maturity. Fraser repeated his warning: You’ll get gaked on.

Every day she would visit the nests, gaining the birds’ trust. Every day, Fraser asked if she had been slimed by giant petrel gak. It never happened.

“He was almost disappointed by that,” she says.

Within two years, she had gained the trust of the giant petrels, which allow her to handle the chicks so she can weigh them and measure their culmen, or beak. A scavenger and predator, giant petrels are roughly the size of a bald eagle, with a hooked beak that can easily rip into whale flesh. They roost on rocky high points across the islands, making their nests out of small stones or discarded limpet shells left behind by gulls.

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.

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.”

NSF-funded research in this story: Bill Fraser, Polar Oceans Research Group, Award No. Award No. 0523261.

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Curator: Peter Rejcek, Antarctic Support Contract | NSF Official: Winifred Reuning, Division of Polar Programs