Albatross Divorce Rates Fly up When Times Are Tough

Sea birds tend to live monogamous lives, mating with the same individual year after year. And albatrosses are often seen as the most committed of them all, normally mating for life.

But occasionally, divorces do take place.

Normally, they are seen as an adaptive strategy so the bird can replace their "sub-optimal" partner. But in research published in the Proceedings of the Royal Society B: Biological Sciences, scientists have found direct evidence that environmental conditions increase divorce rates.

Francesco Ventura, from the University of Lisbon, Portugal, and colleagues studied a population of the long-lived black-browed albatross on one of the Falkland Islands.

The divorce rate among these birds on a "good" year was around one percent. However, during years when environmental conditions were unfavourable, rates increased to around eight percent.

"In long-lived seabirds, social monogamy is the rule rather than the exception and the formation of long-term pair bonds is particularly advantageous given the life history of these animals," Ventura told Newsweek.

"A more familiar mate means a more coordinated partner with which to carry out parental duties and successfully raise chicks.

"Divorce is triggered by previous breeding failures, and females seem to be the initiators of divorce, leaving the former partner to breed with a 'better' mate."

The team looked at mating pairs and divorce rates over these long-term relationships and compared them with warm sea surface temperature anomalies. Years with warmer waters are associated with lower nutrient availability—and colder sea surface temperature anomalies with richer resources.

Their findings showed years with warm sea surface temperature anomalies were linked with higher numbers of breeding pairs getting divorced.

Pairs were found to divorce even if they had bred in previous years, indicating successful relationships were being discarded as a result of the environmental conditions.

"We speculate that this direct effect might be underpinned by high costs of reproduction, which birds pay with later return to the colony, inducing them to arrive at the breeding colony asynchronously," Ventura said.

"The higher physiological stress might be another pathway: in tougher years, females might have higher levels of stress hormones and end up blaming their partner. This is particularly interesting because our results show that warm [sea surface temperature anomalies] mainly acted on previously successful females, i.e. the ones that should have remained with their previous mate."

With climate change, it is expected sea surface temperatures will increase in the coming years and decades. In their paper, the team say environmentally-driven divorce may be an overlooked consequence of the changing planet.

Ventura says the population of albatross they studied is healthy and currently growing, so at the moment shifting to new partners is not such a concern.

"However, this is likely not the case for small populations that are not doing particularly well," he said. "The disruption of pair bonds in a smaller, vulnerable population, with lower availability of alternative partners, might indeed be an issue. And with the current and predicted increase of the ocean temperatures as a consequence of climate change, this issue might become more and more relevant."