Yellow-nosed albatrosses have a new predator
In the middle of the night, an albatross rests on its unique and precious egg. But the large bird is disturbed by the approach of the webbed legs lining the darkness. The albatross stands up to defend its egg, its beak snapping. His nemesis, a beefy male giant petrel, is not here for the egg. With a slit, the petrel bites the albatross around the neck, dragging it into the bushes.
The albatross never returns to its egg.
This feathered violence is new to science. On Gough Island, a lonely rock in the middle of the South Atlantic, researchers recently discovered Southern Giant Petrels, which typically feed on fish, krill and young birds, hunting and killing huge adult albatrosses. .
Gough Island is one of the few breeding grounds for the endangered Atlantic Yellow-nosed Albatross, which has been under the watchful eye of rotating sets of researchers since 2008. The first evidence attacks appeared in October 2017, when researchers discovered the carcasses of 19 adult albatrosses.
At first, they thought the deaths could have been a freak accident; that the albatrosses had crashed in a windstorm, says Michelle Risi, a wildlife ecologist at the Royal Society for the Protection of Birds in the UK. But when she and her colleagues had their turn on the island in 2018, it became clear that the deaths were not due to chance.
“We went back to the area several times to assess the number of adult carcasses and were completely shocked to find several new ones every week,” says Risi.
The team wondered if the deaths were the result of the ravenous invading mice of Gough Island, which fatally harassed the island’s albatrosses. To unravel this mystery, the team returned in 2019 and installed 16 motion-activated cameras near albatross nests. Nearly a million images and over 419 hours of footage revealed that the culprit was male giant petrels, which also breed on Gough Island. The team’s findings, published in a recent study, include images of 11 different petrel attacks, five of which end in the death of an albatross.
Watching southern giant petrels attack albatrosses at night was shocking, Risi says. But at the same time, such a daring predatory maneuver isn’t really out of place.
Southern giant petrels are skillful and greedy scavengers who dominate and haphazardly devour seaside carcasses. But they are also proficient predators. The birds are seagull shaped but the size of a goose and cast an intimidating shadow over the Southern Ocean food chain. Shrewd opportunists, they prey on young or sick penguins and seals, as well as chicks of many species of birds. Giant petrels have even been spotted ripping sperm whale flesh on the surface.
“This is the nature of giant petrels,” says Tegan Carpenter-Kling, an ecologist at BirdLife South Africa in Johannesburg, who is not involved in the study. “They are predatory birds, quite intelligent and ruthless.”
Still, the Gough Island team’s recordings came as a surprise to Carpenter-Kling. “I was shocked. I have never heard of giant petrels scavenging for adult birds unless they are injured.
Richard Phillips, a British Antarctic Survey seabird ecologist who was not involved in the study, points out that attacking healthy adult albatrosses can have immediate and costly drawbacks. “You’d better kill something that’s a lot more defenseless,” he said. ” There is a risk [the giant petrels] will be pecked in the eyes or injured.
It is not yet clear why the southern giant petrels of Gough Island are taking such risks. Theoretically, this could be because they are suffering from a shortage of ocean-sourced food. But Risi believes there should be enough seals and penguins around the island to feed breeding petrels.
It is also possible that the giant petrels have made a habit of exploiting albatrosses already weakened by the constant worsening of the invading mice of the island.
Whatever the cause, the behavior appears to be a recent development limited to Gough Island. Phillips notes that if southern giant petrels were to kill albatrosses elsewhere, there would be cadaver records at some of the other seabird monitoring sites in the Southern Ocean. Dead albatrosses are hard to ignore, given the bird’s vulnerability to introduced predators.
“You would start to think, Was it a cat? Were they rats? You would almost panic, in a way, ”says Phillips.
The albatross killings, however, have bewildering implications for the Atlantic yellow-nosed albatrosses of Gough Island.
“If this behavior spreads and becomes more common in giant petrels, it could certainly pose a threat to the albatross population,” Carpenter-Kling explains, adding that the adult mortality rate is a major factor dictating the trajectory of the albatross. ‘a population.
Phillips estimates that if the few hundred pairs of giant petrels that breed on Gough Island were to become constant albatross killers, “they would probably eat an albatross every few days.”
Predation by southern giant petrels is not the only challenge facing albatrosses on Gough Island. In addition to mice, seabirds are threatened by plastic pollution, climate change and deadly interactions with fishing boats. We “have to solve the anthropogenic problems”, says Risi, “so that predation by giant petrels does not become an additive problem.”
This message appears courtesy of Hakai Magazine.