Climate Change Increases Mate-Swapping in Birds

Birds' long history of infidelity is being exacerbated by global warming


Apparently, humans aren't the only species whose relationships can suffer from stress. According to new research, birds living in unpredictable climates are more likely to "cheat" on their feathered partners.

"Mating with multiple partners improves the chances that at least one chick will have the genes to cope with the variable conditions to come," explained Carlos Botero, an evolutionary ecologist and the lead researcher of the study, published yesterday in the journal PLoS ONE.

Birds typically bond to one partner throughout a breeding season and sometimes nest with the same mate year after year. Before the 1990s, this phenomenon led scientists to believe that more than 90 percent of all species were monogamous, but thanks to improved genetic testing, we now know most birds actually stray from their partners.

Despite birds' long history of infidelity, extreme temperature fluctuations appear to be intensifying the effect. If global climates continue to grow more erratic, the affected areas could see a steady increase of promiscuity among birds, Botero says.

With the help of fellow researcher Dustin Rubenstein, a behavioral and evolutionary ecologist at Columbia University, Botero collected data for more than 200 bird species that included gulls, geese, ducks, sparrows, bluebirds and falcons.

When bringing home food trumps singing
The scientists then compared the birds' mating habits to temperature and precipitation records near the nesting areas. In regions with less stable climates, females were laying more eggs that lacked their spouse's DNA, and birds were swapping mates more often between breeding seasons.

Depending on the location and type of bird, weather fluctuations can create stressful situations that indirectly lead to promiscuity, says Botero. If it's unusually cold, for example, there may not be as many plants or insects to eat, and baby birds may freeze because they haven't grown feathers to protect them from the cold.

It's not only about having the best genes to survive rough conditions, he says, but also how much the male bird can contribute. A tern that brings plenty of fish back to the nest one season may not be able to find any fish the next, prompting his mate to seek out a better partner.

Female birds typically choose their partners based on their perceived attractiveness. Mockingbirds often seduce their mates by singing, while other species may show off hunting skills or colorful plumage. But when weather patterns change, many birds can quickly lose their charm.

"A male that could look very pretty at one point may not look as good when the environment changes, because he's not getting as much food," says Botero. "The quality of a potential mate depends on the context."

Infidelity may sound like a bad thing to humans, but for birds, Botero says, seeking out superior genes could be a useful strategy for surviving climate change.


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