When black-browed albatrosses mate, they're usually in it for life. These giant, regal seabirds can live for up to 70 years. Albatrosses spend the better part of the year sailing above the open ocean alone and only return to mate with their partners on land, where they raise one chick together before flocking out to sea.
By staying together, the couples build trust, communication and coordination—necessities for raising needy chicks year after year. But if a pair can't successfully raise a chick—either the egg never hatches or the chick doesn't survive—the female deems the partnership a bust and they go their separate ways, Katherine J. Wu reports for the Atlantic.
About 15,500 albatross couples live on New Island, which is part of the Falklands in the South Atlantic Ocean. A dataset spanning 15 years revealed that divorce rates among the island's feathery residents fluctuate yearly; as ocean temperatures rose, so did divorce rates. For years, albatross divorce rates hovered at an average of 3.7 percent. But when sea surface temperatures were at their highest in 2017, avian couples were calling it quits at a rate of 7.7 percent, reports Natasha Frost for the New York Times. The team published their findings last week in the journal Proceedings of the Royal Society B.
When water temperatures rise, warm water on the surface doesn't mix well with the cooler, nutrient-rich water below. For the albatrosses, nutrient-poor water means that there is less food—like fish and squid—to feast on, so searching for nourishment will cost more time and energy. By the time the birds return to land to mate, they're in poor health and less likely to breed successfully, which drives breakups, reports Tess McClure for the Guardian.
But in a surprising twist, the team found that even some of the couples that successfully raised chicks still bid each other adieu, the Guardian reports.
"Previous successful females are the ones that are most affected by this [warming]," lead author Francesco Ventura, a biologist at the University of Lisbon, tells Jack Tamisiea for Scientific American. "They divorced more often, when in theory they should have remained together with their previous partner."
When ocean conditions are poor, the albatrosses spend more time at sea and fly further distances to find food. Their extended absence can mess with breeding schedules—for example, they may show up late to mate—and lead to elevated stress hormones. Both can have negative effects on breeding success, Scientific American reports.
"Higher levels of stress hormones in females might lead them to misinterpret this higher stress as a poor performance by the partner and therefore divorce," Ventura tells NPR's Morning Edition.
Ventura calls this the "partner-blaming hypothesis," the Guardian reports.
"Some of these pairs have potentially been raising chicks for decades … and they’re being broken up by things that were entirely out of their hands," Melinda Conners, a marine conservation ecologist at Stony Brook University who was not involved in the study, tells the Atlantic.
Though the albatross population on New Island is still bustling, rising sea surface temperatures fueled by climate change—and therefore higher divorce rates—could impact more susceptible populations of other albatrosses and seabird species, the Guardian reports.
"If you have a situation where increasing sea-surface temperature is leading to higher divorce rates, that reduces breeding success for the population as a whole, " Natasha Gillies, a behavioral ecologist at the University of Liverpool who was not involved in the study, tells Scientific American. "Ultimately, you’re sending fewer albatrosses out into the world, and that’s going to impact the population more widely."