“divorces” among inseparable animals are also on the rise – Corriere.it

One of the unexpected consequences of climate change, and global warming in particular, is the increase in cases of divorce between pairs of monogamous animalsthe. He explains it New Scientist
summarizing the content of several studies that have recently appeared in specialized journals. Monogamy is not widely practiced among vertebrates. Less than 5% of mammals form monogamous pairs, at least for a part of their life, among these the beavers. Few species of monogamous fish, the best known are the sea ​​horses. There monogamy, on the other hand, is much more widespread among birds, of which it reaches 80%. However, the researchers have observed that even among birds things are changing under the pressure of climate change that modifies habitats. With the result that in the short term the break of monogamy can be advantageous for the individual, but in the long term it is a disadvantage for the species.

The two cases of monogamy

Often we humans are led to judge animal behaviors based on our own. Monogamy in animals, on the other hand, has nothing to do with ethics, morals, religion, traditions or society, but is based solely on the evolutionary advantage of the species. The high percentage of monogamy among birds is explained by the fact that the incubation of the eggs and the growth of the chicks may require the presence of two adults, which is perfected only after several broods (for bird species that live longer). . Furthermore, a tested couple, with the experience acquired, can better face the changes in the living habitat. Biologists now distinguish between genetic monogamy and social monogamy. In this second case, the members of the couple can also mate with individuals outside the couple under certain conditions. Both conditions, however, can end in a divorce that has different causes but essentially attributable to a single one: reproductive success or failure.

Falkland albatrosses

But things are more complicated. In the Falkland Islands, 500,000 monogamous pairs of black-browed albatross (Thalassarche melanophrys). Females lay only one egg per clutch, but if it does not hatch, these pairs are five times more likely to break up than those that manage to complete the clutch. Researcher Francesco Ventura of the Woods Hole Oceanographic Institution, who has been studying these birds for fifteen years, has discovered that with the warming of the sea, the divorce rate of couples who have successfully terminated the brood has risen to 8%. With warmer seas, albatross food supplies decrease and birds have to travel greater distances to feed. In birds it causes us to increase the level of the stress hormone, similar to cortisol. According to Ventura, a stressed and hungry female could see the cause of her problems in her partner, decide to change him and thus, according to another research, increase the chances of her reproductive success by choosing a male with a better territory. Similar phenomena have also been recorded in some penguin species.

Long-term losing behavior

But there is the reverse of the medal. Other studies have shown that if the choice to break the monogamous relationship can be a winner on an individual level, instead a loser in the long term for the coloniesin particular for those that nest with few specimens in remote oceanic islands. The new couples lack the experience gained over the years by the established ones: The overall reproductive success of the monogamous bird population decreases as the rate of pair breakup increases, explains Brian Lerch of the University of North Carolina. Another unexpected consequence of global warming which is rapidly altering ecosystems around the world.