Warming, taller shrubs may affect birds breeding on tundra

More shrubs moving onto Arctic tundra because of climate change will have minimal effect on many of the bird species that breed there, but birds likely will seek other habitat when the shrubs grow tall, according to a new federal study.

A study by the U.S. Geological Survey concludes that the size of the shrubs was more critical than the density in determining whether birds would continue in the habitat.

“Height came out to be the most indicative of bird habitat selection,” said Sarah Thompson, a USGS research wildlife biologist based in Anchorage and the lead author of the study.

Multiple studies have shown that tundra areas are getting more shrubs, Thompson said. Climate warming also is having effects in the form of longer growing seasons, thawing permafrost and more frequent and intense wildfires, the authors said.

“All across Alaska, you see this kind of shrub encroachment into places that previously didn’t have shrubs or didn’t have tall or many shrubs,” Thompson said.

The researchers over three summers studied 17 bird species on the Seward Peninsula, which juts 200 miles into the Bering Sea in western Alaska and includes the city of Nome. The peninsula, Thompson said, is ideal for study because it in- cludes coastal habitat and inland settings at a variety of elevations. It’s also along the transition between boreal forest and tundra, Thompson said.

The research did not attempt to explain why tall shrubs made tundra less appealing to birds, such as effects on nesting or insects. That likely will be addressed in future studies, she said.

George Divoky, director of the nonprofit Friends of Cooper Island, who has studied Arctic seabirds for more than four decades off the coast of northern Alaska, said the study is one more piece of evidence that the warming Arctic is having effects both at sea and on land to avian populations.

However, he said, the paper only emphasized shrubs instead of other important factors affecting birds on the peninsula, such as warmer temperatures and birds’ dependence on seeds and insects.