Birds of a feather
Researcher finds special bond — and discoveries — among giant petrels
Posted February 26, 2010
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. …
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. …
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. …
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. …
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.”