Divorce rate in albatrosses influenced by environment | Polarjournal
Black-browed albatrosses are the most common species in the Falkland Islands. The medium-sized animals can live up to 70 years and usually form a monogamous relationship when they become able to breed from the age of 10…. at least as long as the external conditions are right. Picture: Michael Wenger

Albatrosses are not only popular with many people because of their soaring skills and elegant appearance. Their way of life also fascinates both researchers and laymen. Particularly their ability to enter pair-bonds on lifetime and to find the same partner again in the colonies every year makes the seabirds very popular. But also with them divorces occur, which are even intensified by external conditions. This is the conclusion of a long-term study by an international research team.

The scientists studied the long-lived black-browed albatrosses on New Island, one of the approximately 770 islands in the Falkland archipelago, where around 15,500 breeding pairs live. It was found that in years when food conditions were poor and sea surface temperatures were elevated, pairs formed new partnerships the next year. It was mainly the females that were looking for a new partner. The team led by Francesco Ventura of the University of Lisbon, the lead author of the study, discovered that females who had lost their chick the year before were 5 times more likely to divorce. Overall, the divorce rate was found to be between 1 and 8 percent. “Environmentally driven divorce may be an overlooked consequence of global change,” the researchers conclude in their paper.

Black-browed albatrosses breed in large colonies on the windswept slopes of the Falkland Islands and sub-Antarctic islands. They brood on skillfully manufactured pot-similar loam-nests. The study shows that females are the choosiest sex when it comes to pair-bonding. Picture: Michael Wenger.

The research team collected the data that led to the results of the study over a period from 2004 to 2019. They followed the life histories of 463 female and 477 male birds. If one partner of a couple who had been together one year turned to a new partner in the spring of the following year (and the old partner was still alive), this was considered a divorce. This allowed the team to study a large number of pair bonds and fit them into a population model. By comparing this with various environmental data that had then prevailed in the corresponding years, the team was able to calculate the probability of divorce in the following year. This showed that food availability, which is also controlled by water temperatures, among other factors, resulted in animals returning to their mate in spring in a worse condition. This made them a poorer choice as partners. Here it became clear that it is mainly the females that are choosy about this. If the partner did not conform to the image of a “strong” male, she was much more likely to seek a new partner.

Black-browed albatrosses usually raise one young, which hatches after 68 days of incubation. Afterwards, the adults must bring in squid and fish during 120-130 days in order to let the young reach fledgling stage.. The birds can travel long distances to find food. Picture: Michael Wenger

Black-browed albatrosses usually raise only one young each year. Between September and November, the couples come together, renew their pair bond or look for a new partner, and then mate. The single egg is incubated for 68 days, with the partners feeding each other and taking turns. When the chick hatches, it takes about 120 – 130 days until it is fledged. During this time, the parents must bring in enough food in the form of squid and fish to feed the young. The study showed that females who lost their young during this period were about five times more likely to change mates the next year than those whose young survived. According to the scientists, this leads to a higher level of stress in the females and thus to the search for a new mate. In the face of predicted climate changes that will not stop at sub-Antarctic waters, this should be bad news for male Black-browed Albatrosses. Seabirds are not considered to be at immediate risk. But add this stress to the already prevailing dangers of longline fishing and pollution, and the population is likely headed downhill.

Dr Michael Wenger, PolarJournal

Link to the study: Ventura Francesco, Granadeiro José Pedro, Lukacs Paul M., Kuepfer Amanda and Catry Paulo 2021Environmental variability directly affects the prevalence of divorce in monogamous albatrossesProc. R. Soc. B.2882021211220212112 http://doi.org/10.1098/rspb.2021.2112

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