Why Strange New Birds Are Appearing in Your Backyard

As temperatures rise, southern species are flying north for the winter and pushing out local birds.

(Photo: Getty Images)

Oct 21, 2014· 1 MIN READ
Katharine Gammon has written for Nature, Wired, Discover, and Popular Science. A new mom, she lives in Santa Monica.

Scientists have confirmed for the first time what bird-watchers have been saying for years: There’s a new set of visitors to your backyard feeder.

Winters are slowly getting warmer, with fewer snowy days, and those small but steady environmental changes affect the type of birds that can survive in northern climates.

“Winter birds have always been sentinels of climate change,” said Benjamin Zuckerberg, a biologist at the University of Wisconsin–Madison and coauthor of a new study published in the journal Global Change Biology. “They’re living life on the edge, with limited resources.”

In some cases, the southern species may start crowding out the northern ones, pushing them to higher latitudes. “Northern-adapted species are vacating areas,” said Zuckerberg. “While many of these birds still have ranges in Canada, they may potentially get out-competed by southern birds.”

Zuckerberg and his colleague Karine Princé tapped 22 years of data collected by backyard bird-watchers in the eastern United States. Those citizen-scientists tallied the number and distribution of 38 bird species at their feeders and contributed it to Project FeederWatch at Cornell University's Cornell Lab of Ornithology.

The scientists found that that mix of birds is creeping ever northward, having moved 93 miles from 1990 to 2011. That has changed the composition—and competitive fitness—of birds that spend their winters in northern latitudes.

In particular, birds such as cardinals, chipping sparrows, and Carolina wrens —which generally stay in warmer southern climates and have short migrations—have been making their way north over the winters.

Backyard bird-watchers provide a great depth of data for scientists. Around 53 million Americans have bird feeders at their homes, and that number has stayed relatively steady since the ornithologists started collecting data. Over the years, the data has been used to analyze migration times, the spread of bird diseases, and the effect of urbanization.

The researchers also looked at the effects of sudden winter cold snaps on warmer-climate birds. They concluded that quick drops in temperature may kill off the newcomers.