Thursday, December 01, 2022

Research shows that climate change is causing some albatrosses to “get divorced”

Research shows that climate change is causing some albatrosses to "get divorced"

MELBOURNE, Australia – Albatrosses usually mate for life, making them some of the most monogamous creatures on the planet. But climate change could push more birds to “divorce,” according to a study published last week by the Royal Society of New Zealand.

15,500 breeding pairs of black-browed albatrosses on New Island in the Falkland Islands used 15 years of data. Researchers led by Francesco Ventura of the University of Lisbon found that the bird divorce rate, averaging 3.7 percent over this period, increased during the warmest years. In 2017, it grew to 7.7 percent.

Breeding albatrosses is usually very rare. The report notes that the most common factor leading to final separation is the chick’s inability to successfully lean. During those years when the sea was unusually warm, albatrosses were more likely to struggle with fertility and bred – a technical term used by researchers – foreshadowing an alarming trend for seabird populations in general as temperatures rise around the world.

“The rise in sea surface temperatures has led to an increase in the divorce rate,” said Mr Ventura, an environmental biologist, in an interview.

But even after the models accounted for a higher breeding failure rate in warmer years, that alone did not explain the rise in divorce rates, the researchers found. “We see that something else remains unexplained,” said Mr Ventura.

Large seabirds are found in the Southern Hemisphere, in countries such as New Zealand and off the coast of Argentina. They are known for their extensive travel, wingspan of up to 11 feet, and long life. They can live for decades. Black-browed albatrosses derive their name from billowing, smoky brows that give them an expression of everlasting irritation.

Albatrosses in partnership spend most of the year separately, reuniting each season to raise chickens together. The male usually arrives first on land, where he waits for his mate and looks after their nest.

“It’s clear that they love each other,” said Graham Elliott, an albatross expert with the New Zealand Department of Conservation, who was not involved in the New Island exploration. “After observing albatrosses for 30-40 years, you may notice this. They do everything that we think is important – human emotions, you know – they greet their long-lost spouse, and they love each other, and they will have a child. It is wonderful.”

Birds usually return to the same mate every breeding season. Couples perform a reunion dance that has become increasingly synchronized over the years. “Over the years, they have improved the quality of the work – at first a little awkward, and then, over time, they get better and better and better,” said Mr. Ventura.

Stress from warmer seas seems to upset this delicate balance, especially if birds arrive late for the breeding season or are in poorer health after moving farther in search of food.

“We expect cooler water to be associated with nutrient-rich and resource-rich conditions, while warmer water is resource-limited conditions,” said Mr Ventura.

The researchers found that some albatrosses in the study population completed successful mergers and reunited with another albatross. (Women who find it easier to find a new partner tend to initiate permanent separation.)

“After a difficult breeding season with limited resources, greater effort and higher investment in breeding can lead to stressed females to sever ties with their previous mate and look for a new one, even if it was previously successful.” researchers.

Dr. Elliott, an expert on New Zealand albatrosses, said the study results “don’t surprise me that much.” Researchers have noticed demographic changes among birds elsewhere as fish populations have declined, he said.

According to the New Zealand Department of Conservation, the number of albatrosses in the outer Antipodes Islands, about 530 miles south of New Zealand, has declined by two-thirds in the past 15 years.

Climate change is a factor: female birds have gone astray in search of food that is harder to find, leading them to fatal contact with fishing boats and a significant imbalance in the population, Dr. Elliott said.

This prompted the lonely male albatross to make desperate decisions, he said. Male-male pairs currently make up 2 to 5 percent of the island’s bird population, mimicking same-sex mating behavior in many species.

“There are now one and a half to two times more men than women on the island,” said Dr. Elliott. “We started to form these male-male pairs – males can’t find a mate, and after a while they decide that other males are better than nothing.”

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