Melbourne, Australia Albatrosses generally mate throughout life, forming one of the most homogeneous species on the planet. But climate change is pushing birds to “divorce,” according to a study released last week by the Royal Society of New Zealand.
The study of 15,500 breeding pairs of black-eyed albatrosses on New Island in the Falkland used data that lasted 15 years. According to researchers led by Francesco Ventura of the University of Lisbon, the bird divorce rate, which averaged 3.7 percent during that period, increased during the warmer seas. In 2017, it rose to 7.7 percent.
Albatross divorce is generally very rare. The report notes that the most common trigger for permanent separation is the inability to successfully repel chicks. In years when the seas are unusually hot, albatrosses are more likely to struggle with fertility and divorce a technical term used by researchers as the global warming generally foretells a worrying trend for seabirds populations.
“Rising sea surface temperatures have led to an increase in divorce,” Mr. Ventura, a defense biologist, said in an interview.
But the researchers found that although the samples contributed to higher reproductive failure in the warmer years, it did not explain the rise in divorce rates. “We see something still unexplained,” he said. Ventura said.
Large seabirds are found throughout the southern hemisphere, in countries such as New Zealand and off the coast of Argentina. They are known for their wide travel, wingspan up to 11 feet and long life. They can live for decades. Black-browed albatrosses got their name from the swapping, mouse eyebrows that give an expression of perpetual irritation.
The albatrosses in the congregation set aside most of the year and re-assemble the chicks each season. The male usually arrives first on the ground, where he waits for his mate and heads for his nest.
Graeme Elliott, an albatross expert in the New Zealand Department of Defense who has not been involved in New Island research, said: “It is clear that they love each other. Congratulations to the long lost spouse, they love each other and they are going to have a baby. It’s wonderful.
Birds usually return to the same mate at each breeding season. The couple performs a reunion dance that has been synchronized for years. “They improve the quality of performance over the years at first a little disgusting, and then, as time goes on, they get better and better and better,” he said. Ventura said.
The pressure of the hot seas seems to upset that delicate balance, especially if the birds are late for the breeding season or fly long distances to find food and are in poor health.
“We expect cold water to be associated with more nutritious and more fertile conditions, while hot water is more resource-poor conditions,” he said. Ventura said.
The researchers found that some albatrosses in the population ended up successful unions and reunited with other albatrosses. (Women have an easy time finding a new partner, and they are prone to permanent separations.)
“After a difficult fertile breeding season, more effort and more reproductive investment can lead depressed women to break the bond with their ex-partner and seek something new, even if previously successful,” the researchers wrote.
New Zealand Albatross Specialist Dr. Elliott said the study’s finding did not “surprise me.” Researchers have observed population changes among birds elsewhere as the number of fish has decreased, he said.
The New Zealand Department of Defense says the number of albatrosses in the remote Antibots Islands, about 530 miles south of New Zealand, has dropped by two-thirds over the past 15 years.
Climate change is a factor: female birds travel well in search of hard food, being dragged into deadly contact with fishing boats, leading to significant population imbalances, Dr. Elliott said.
This, in turn, prompted male albatrosses to make desperate decisions, he said. Male-male pairs now make up 2 percent to 5 percent of the island’s bird population, echoing the pattern of same-sex mating behavior across many species.
“We now have one and a half to two times more men on the island than women,” Dr. Elliott said. “We’ve been creating these male-male pairs men can’t find a mate, and after a while, they decide other men are better than anything.”