In 2012, the separation of two major celebrities was relayed by the press. Bibi and Poldi, two giant Galapagos tortoises, housed at the Happ reptile zoo in Austria, suddenly left each other after more than a century of living together. A particularly violent rupture, the female having torn a piece of the shell of her companion before attacking him, until the park staff transferred him to another enclosure.
Like most mammals, Galapagos tortoises are not monogamous. Within the animal kingdom, man is rather an exception: social monogamy has been observed in less than 10% of mammals. Conversely, birds tend to form life partnerships, underlines the British daily The Guardian. According to researchers, social monogamy and sexual monogamy of birds do not necessarily go hand in hand, and can cause divorce, as in humans.
Before talking about divorce, you still need to form a relationship. According to Professor Simon Griffith, an evolutionary ecologist at Macquarie University (Australia), the low rate of strong, long-lasting relationships in animals can be explained by the difference in parental investment between males and females. In most mammal species, parental care is primarily provided by the female, who invests heavily in the gestation and nursing of her young.
However, in birds, the situation is completely different. “The father may care almost as much as the female about providing food. This is why birds tend to form partnerships, unlike mammals.explains Simon Griffith.
The albatross, the most faithful
Previously, data suggested that birds were primarily sexually monogamous. Thus, more than 90% of known birds mate sustainably, as noted by Raoul Mulder, evolutionary ecologist at the University of Melbourne. However, his research on Great crested wren reveal that 76% of chicks born in nests are in fact fathered by other males. This astonishing cuckolding rate is only surpassed by that of the Australian magpie, which reaches 82%.
Among birds, the wandering albatross is probably the one that most embodies monogamy. Can live up to 50 years, they generally mate for life. “This bird needs a lot of time to establish a pair bondsays Ruijiao Sun, postdoctoral researcher at the University of California at Santa Barbara. If an individual loses their partner, it takes years to bond with a new partner and be able to start reproducing again..»
Short-lived species, on the other hand, might be more inclined to get rid of their partners to maximize reproductive opportunities. Despite this, Ruijiao Sun’s research indicates that the divorce rate among wandering albatrosses is around 10%. For comparison, the king penguin, although sexually monogamous when pairing, divorces at a rate of about 80%.
Another factor in divorce: the climate crisis. In a study on the snow petrelswhich nest in rock crevices in Antarctica, Ruijiao Sun and co-authors found that the number of snow days during a breeding season was directly related to breakup rate. Too much snow fills the nests and freezes the eggs, causing incubation to fail.
Declining sea ice due to climate change will likely affect survival rates in the future, skewing the sex ratio. “We will have many males in a population and fewer females available to mate with them”details Ruijiao Sun. Yet another problem caused by climate change: rain is already affecting bird divorce, as we explained in November.
Source: www.slate.fr
