Climate Change Impact No. 326: The Birds Start Sleeping Around

Whooper Swan (Cygnus cygnus) pair arguing at wintering site, Kussharo-ko, Hokkaido, Japan. Photographer: Konrad Wothe/Minden Pictures

Those monogamous birds? Another casualty of climate change.

As it gets hotter here on Earth, they're more apt to start cheating on each other, according to the U.S. National Climate Assessment, released today.

Scientists have said for years, decades even, that climate change is going to be rough. Storms, fires, heat extremes -- the works. The research tends to get more solid and detailed every year. It's all laid out in the Assessment, and it's mostly a bummer.

But this bird-divorce bit is an angle few saw coming. Everything is easier in hindsight.

"Climatic fluctuations increase the probability of infidelity in birds that are normally monogamous."

-- U.S. National Climate Assessment

The Assessment, which comes out every four years, cites a 2012 paper published in the journal Plos One, titled "Fluctuating Environments, Sexual Selection and the Evolution of Flexible Mate Choice in Birds." Or, in the tabloid version: "Birds Get Hot, Start Spouse-Swapping, Page 4."

The 2012 study reviews the scientific literature about bird infidelity -- or having extramarital offspring -- in 122 avian species. It also looks at what the authors actually call "divorce," or starting a new nest, in 86 species. The study shows "significant associations between environmental parameters and the incidence of avian infidelity and divorce."

The cheating makes sense once the authors walk through the logic and evidence. When the environment changes, different traits can become more attractive to prospective mates. For example, if it's suddenly drier and you are going to have to dig deeper for worms, it might be nicer to have a spouse with a bigger beak (if you follow me).

All these broken nests, tumultuous in the short term, could end up making species more resilient to unpredictable environments. More pairings, and more offspring, mix up the gene pool. That increases the chances that young tweeters will be born with traits better suited for the new conditions.

Humans are pretty good at insulating themselves from the natural world, which makes an analogous study of modern marriage pretty hard to conduct, according to lead author Carlos Botero of the National Evolutionary Synthesis Center. Income, market volatility and prices are things that affect our lives more directly than longer growing seasons do.

Still, "I wouldn't completely discount the effects of simple environmental variables," like precipitation and temperature, Botero said by email. "They clearly have effects on our economy," he said. "We know they affect our behavior in meaningful ways."

More by Eric Roston (@eroston on Twitter):

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