Some pied flycatchers, a common migratory bird slightly smaller than a sparrow, are missing their spring meals and dying as a result of climate change, a team of scientists reported this week. The discovery is one of the most sophisticated showing the domino effect of shifting seasons and their impact on predators and prey.
The migratory birds fly thousands of kilometers each spring from wintering grounds in Africa to Europe, where they breed. In 2001, scientists with the Netherlands Institute of Ecology found that the flycatchers' reproduction suffered because they arrived in Europe too late to have much time to breed. Now, University of Groningen evolutionary ecologist Christiaan Both worked with scientists from the institute and measured how many caterpillars were available for the birds to eat by weighing the insects' droppings. Caterpillars, they learned, have responded to an earlier spring by moving up their peak emergence by 16 days.
But some of the birds are only breeding a week earlier than they used to--and their young are consequently missing out on many meals. "It's impossible for them to predict when the spring starts in Europe," says Both. That's had a profound impact, the team reported in the 4 May Nature. Among nine flycatcher populations they studied over 2 decades, the researchers found that those that mistimed their arrival declined in number by a stunning 90%, compared to better-synchronized groups that suffered only a 10% drop. Both hopes that genetics will help explain why some pied flycatchers are leaving Africa sooner. Both is also hoping to begin tracking birds to see if they are adapting by migrating to European areas further north.
"It's a really important piece of the puzzle," says Cornell University ornithologist David Winkler, who reviewed the paper for Nature. "He's adding detail to the avian response to climate change that we don't have elsewhere." Scientists are only beginning to learn how climate change alters the timing of ecological interactions, but many suspect the cross-species impacts are going to be great. Both's work, Winkler says, suggests that other studies may be missing the fact that even when the birds migrate sooner, they might still be missing food or other ecological needs.