Migratory Birds’ New Climate Change Strategy: Stay Home

• By Brandon Keim
• 
  

Birds may have an unexpected strategy for adapting to climate change. In addition to migrating at different times to newly hospitable locales, they may also shorten their migrations, expending energy on breeding and eating rather than flying.

“There’s lots of data on bird arrival and bird breeding times, and that gives the impression that these are the most important phenomena,” said zoologist Francisco Pulido of the Complutense University of Madrid. The basic impulse to migrate is likely just as important, “but it’s been much more difficult to show, and so it hasn’t been appreciated,” he said.

Pulido and Max Planck Institute ornithologist Peter Berthold describe patterns found in 13 years of data from a southern German population of blackcaps, a common migratory songbird, in a study published April 5 in the Proceedings of the National Academy of Sciences.

As temperatures in central Europe have risen, blackcaps have arrived earlier at summertime breeding areas and departed later for their winter homes. Some researchers have predicted blackcaps would also migrate over ever-shorter distances, and in some cases stop altogether, allowing them to save energy and concentrate on finding food and mates. But this hadn’t been tested.

To gauge the birds’ migratory energies, Pulido and Berthold removed a few hundred blackcaps from the local population each summer. As captive birds are restless during the time they would typically be migrating, the researchers used them to measure the duration of wild migrations. These dropped slowly but steadily between 1988 and 2001, in keeping with predictions.

(Most of the captured birds were released at the end of each season, eventually catching up to their compatriots.)

In a second part of the study, Pulido and Berthold bred the most sedentary blackcaps. They wanted to accelerate the natural trend, seeing in a few years what would normally take decades. From this, they extrapolated that some blackcap populations could stop migrating altogether within 40 to 50 years. Other birds may do the same.

The next step in the research is connecting changes in migratory impulse to other adapations. Pulido speculates that shorter distances facilitate earlier arrivals, which in turn alter patterns of reproductive development.

However, shorter distances may only be an option for some species. Blackcap migration spans a relatively modest 1,000 miles, and sometimes less. For birds that travel thousands of miles, with no hospitable territory between their destinations, there may be no middle ground.

Blackcaps are also quite common. Species with smaller populations may be more vulnerable to weather extremes that become more common with warming, said Pulido.

“Adaptation requires a large population. Otherwise they’ll go extinct,” he said.

Image: Ignacio García/Flickr

Sphere: Related Content