Experts are unclear why giant petrels attack healthy adult albatrosses, despite the risks of being pecked in the eye or injured.
Scientists have discovered that the southern giant petrel (Macronectes giganteus) hunts and kills large numbers of the Atlantic yellow-nosed albatross (Thalassarche chlororhynchos) on Gough Island, as reported by Smithsonian on July 17. Gough Island is one of the few breeding sites for the Atlantic yellow-nosed albatross, a species that has been closely monitored by researchers since 2008.
The first evidence of these attacks appeared in October 2017, when researchers found the carcasses of 19 adult albatrosses. Initially, they believed these birds died due to accidents, such as crashing to the ground in stormy weather, according to Michelle Risi, an ecologist at the Royal Society for the Protection of Birds (RSPB). However, upon returning to the island in 2018, Risi and her colleagues realized they did not die from accidents.
To find the exact cause, the research team returned in 2019 and installed 16 motion-detecting cameras near the albatross nests. Nearly a million photographs and over 419 hours of video footage revealed that the culprit was the southern giant petrel, which also breeds on Gough Island.
The southern giant petrel is a skilled scavenger but also an adept predator. This species resembles a seagull but is as large as a goose. They are intelligent and opportunistic, frequently attacking young birds, penguins, and small or weak seals, and at times even tearing apart dead sperm whales that have surfaced.
However, Tegan Carpenter-Kling, an ecologist with BirdLife South Africa, was shocked to learn that they were attacking healthy adult albatrosses. “I had never heard of giant petrels hunting adult birds unless the prey was injured,” he stated.
Attacking healthy adult albatrosses carries significant risks, according to Richard Phillips, a seabird ecologist at the British Antarctic Survey (BAS). “Giant petrels could be pecked in the eye or injured,” he said.
Southern giant petrels are skilled scavengers but also adept predators.
Experts are still unsure why the giant petrels on Gough Island are taking such risks. Theoretically, they may be lacking food at sea. However, Risi believes there are still enough seals and penguins around the island for them. It is also possible that the giant petrels have developed this behavior by opportunistically attacking albatrosses that are already weakened by disturbances from rats.
“If this behavior spreads and becomes more common among giant petrels, the albatross population will certainly be threatened,” Carpenter-Kling commented. He also noted that the mortality rate among adult birds is a significant factor affecting population growth.
The southern giant petrel is not the only challenge that the albatrosses on Gough Island face. They are also threatened by invasive rats, plastic pollution, climate change, and fishing activities.
