AS THE song would have it, birds, bees and even educated fleas fall in love. For some birds, however, the love turns sour 鈥� they get divorced.
Many birds may seem like model parents, with males and females investing more equally in caring for their young than the average mammal. While 85 per cent of bird species are socially monogamous 鈥� they form pair bonds and share the workload 鈥� divorce is common, occurring in 92 per cent of these species, including the humble great tit (pictured).
By analysing data recorded from across 64 species, at the University of Oxford and colleagues found that birds were most likely to divorce when their breeding success was low ().
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Culina found the signs of a doomed partnership emerge early 鈥� pairs in which the female produced a low number of eggs or laid them relatively late were less likely to stick together for a second breeding season. It is possible that unimpressed males may decide they can do better. But females are believed to have some control over the number of eggs they lay, so a small clutch size may actually be a sign of female discontent, says Culina. 鈥淚t might be that she鈥檚 already made the decision, and because she doesn鈥檛 like him very much, she won鈥檛 make many eggs.鈥�
鈥淒ivorce can be beneficial or detrimental for an individual,鈥� says of the University of Bath, UK. 鈥淏y ditching a poorly performing mate, a bird may well hope to find a better one.鈥� But he says divorce can have disastrous consequences, especially if there aren鈥檛 many other males or females to choose from.
Culina鈥檚 study found that, when birds do break up, it鈥檚 the females that benefit. 鈥淔emales who divorce gain better breeding success with a new partner, but males who divorce show no improvement,鈥� she says. This might indicate that it is the females that decide it鈥檚 time to find a new mate. A male wanting to leave a partner risks leaving territory, too 鈥� so they may have more to lose.
How does a bird decide whether to stay or go? Do they monitor each other鈥檚 behaviour, for example? Not much is known, says Sz茅kely.
This article appeared in print under the headline 鈥淲hy bird break-ups are bad news for the boys鈥�
