In Costa Rica, Younger Bird Species Are Better Equipped to Survive Mankind

A new study of birds in Costa Rica found that while human conversion of rain forests into farms is pushing some species towards extinction, more recently evolved species are better adapting to life on agricultural sites.

The conclusion is profound: human manipulation of the Costa Rican landscape is fundamentally restructuring the tree of life, favoring newer species over the more ancient ones.

Researchers from Stanford University and the University of California, Berkeley studied 44 plots of land that represented three different types of land use in Costa Rica: natural rainforests, agriculture sites with multiple types of crops, and industrial monoculture farms that only support one crop.

Using a massive data set of 118,127 sightings of 487 species of birds and a phylogeny of birds created by Yale University's Walter Jetz in 2012, the researchers developed a new model to estimate when and where a species of bird disappeared from a landscape.

"What we're able to show was that as time progressed, it was the evolutionary extinct, the ancient species, that go extinct locally in agriculture and have a harder time re-colonizing," Luke Frishkoff, a doctoral student a Stanford and lead author of the study, told me. "Younger ones are able to colonize, and once they have they stick around."

What they don't know is exactly why these younger species are adapting, or what is limiting the older ones. One theory is that birds that evolved to live in a savannah, which developed more recently than rainforests, are pre-adapted for life in agricultural sites, but at this point it's just educated speculation.

They did conclude that smaller, diversified farms are much better at supporting ancient species than the massive industrial plots. A large volume of research has shown that more diverse farms harbor more biodiversity than monoculture farms, so this doesn't come as much of surprise.

Simply planting a tree among the crops goes a long way to protecting millions of years of evolution. Frishkoff said that the diverse farms, with more vegetation, natural boundaries instead of fences, and multiple crops, were home to nearly 600 million more years of evolutionary diversity than the massive monoculture sites.

While protecting life should be a no-brainer, it actually has benefits for humans, the researchers said. A diversified genetic pool is better able to respond to sudden changes, sort of like a diversified stock portfolio is smarter than throwing all your money into one investment.

"The more birds you have on your plantation, the more you can mitigate pest outbreaks, for example," said David Karp, a researcher at Berkeley who co-authored the study. Karp previously wrote an article explaining how conserving biodiversity of birds is actually improving the yields of coffee farms.

Next, the researchers want to take a closer look at the birds that are surviving in agriculture sites to identify which traits allow them to adapt. By adapting agricultural landscapes to help these traits, humans can create smarter farms that improve their crops as well as buffer against extinction.