A Chickadee Mating Zone Surges North

New York Times, March 18, 2014

In a long, narrow strip of territory from Kansas to New Jersey, two closely related species of chickadees meet, mate and give birth to hybrid birds. Now scientists are reporting that this so-called hybrid zone is moving north at a rate that matches the warming trend in winter temperatures.

“It has moved north by about seven miles in the last 10 years,” said Scott Taylor, an evolutionary biologist at the Cornell Lab of Ornithology at Cornell University.

The northward movement of the strip “corresponds so closely to warming global temperatures,” Dr. Taylor said. “The fact that these little birds are experiencing this makes it really relatable.” (The species are the Carolina chickadee, from the South, and the black-capped chickadee, from the North.)

The scientists, who reported their findings in the journal Current Biology, relied on blood samples drawn from chickadees in Pennsylvania from 2000 to 2002 and from 2010 to 2012, and on sightings of hybrid chickadees recorded in the citizen science database eBird. They found that hybrids were sighted in areas where the average low temperature in winter was 15 to 19 degrees Fahrenheit (minus-9 to minus-7 Celsius) — the same readings as a decade earlier, but in a zone seven miles north of the 2000-02 sightings.

The adaptability of the chickadees is impressive, Dr. Taylor said, but less mobile organisms that cannot move as fast may be suffering.

For these organisms — like small mammals, insects and plants — the warming temperatures could have serious implications that are not immediately apparent, he said.

SINDYA N. BHANOO