Birds that migrate long distances tend to be more likely than others to break up with their partner, according to an analysis of 232 species.
About 90 per cent of bird species are socially monogamous, meaning they form couples that primarily breed with each other and raise offspring together. Some of these couples stay together for life, while others end up getting “divorced” and moving onto new partners.
To identify factors that lead to bird break-ups, Ěýat Sun Yat-sen University in China and his colleagues studied 232 species with documented divorce rates in , Birds of the World.
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They found that species that migrate particularly long distances each year to obtain food between breeding seasons typically have higher rates of splitting up.
Great blue herons (Ardea herodias), for example, migrate and have a divorce rate of .
This may be because travelling further makes it harder for members of a couple to return home at the same time for their annual breeding season, says at the University of New England in Armidale, Australia. They may get delayed by storms or other weather events, she says.
“If you’re the one who gets back first, it’s risky waiting for your partner because you don’t know if they’ll show up – they may have died or been blown off course,” says Kaplan. Finding a new partner may seem a safer bet even if it requires extra energy to go through another courting process, she says. “Breeding seasons are often quite short so you don’t want to miss out.”
at Monash University in Melbourne, Australia, says it makes sense for birds with long migrations to have higher divorce rates, but says there are some exceptions.
Black-tailed godwits (Limosa limosa islandica), for example, migrate more than 1000 kilometres from Iceland to the UK or south-west Europe each year but have relatively low divorce rates.
This seems to be thanks to an uncanny ability to synchronise with their partners, says Peters. Although members of a couple will follow separate migration paths and typically end up , they are somehow able to return to their breeding ground in Iceland at almost the same time, which reduces the risk of break-ups, she says. “But most birds are not able to do that – it’s a pretty amazing feat.”
Other factors that have been found to lead to bird couples splitting up include low breeding success, Ěýand .
BioRxiv
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