[Maine-birds] Black-capped and Carolina Chickadees shift their ranges north - longish

This from Cornell

Chickadees in poleward range shift

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Cornell University

PUBLIC RELEASE DATE:

6-Mar-2014

Contact: Joe Schwartz

Joe.Schwartz@cornell.edu

607-254-6235

 

Warming temperatures are pushing 2 chickadee

species -- and their hybrids -- northward

 

DNA sleuthing confirms chickadee 'hybrid zone'

marching northward as climate warms

 

The zone of overlap between two popular, closely

related backyard birds is moving northward at a

rate that matches warming winter temperatures,

according to a study by researchers from the

Cornell Lab of Ornithology, Villanova University,

and Cornell University. The research will be

published online in Current Biology on Thursday,

March 6, 2014.

In a narrow strip that runs across the eastern

U.S., Carolina Chickadees from the south meet and

interbreed with Black-capped Chickadees from the

north. The new study finds that this hybrid zone

has moved northward at a rate of 0.7 mile per

year over the last decade. That's fast enough

that the researchers had to add an extra study

site partway through their project in order to

keep up.

 

"A lot of the time climate change doesn't really

seem tangible," said lead author Scott Taylor, a

postdoctoral researcher at the Cornell Lab of

Ornithology. "But here are these common little

backyard birds we all grew up with, and we're

seeing them moving northward on relatively short

time scales."

 

In Pennsylvania, where the study was conducted,

the hybrid zone is just 21 miles across on

average. Hybrid chickadees have lower breeding

success and survival than either of the pure

species. This keeps the contact zone small and

well defined, making it a convenient reference

point for scientists aiming to track

environmental changes.

 

"Hybridization is kind of a brick wall between

these two species," said Robert Curry, a

professor of biology at Villanova University, who

led the field component of the study. "Carolina

Chickadees can't blithely disperse north without

running into black-caps and creating hybrids.

That makes it possible to keep an eye on the

hybrid zone and see exactly how the ranges are

shifting."

 

The researchers drew on field studies, genetic

analyses, and crowd sourced bird sightings. First,

detailed observations and banding data from sites

arrayed across the hybrid zone provided a basic

record of how quickly the zone moved. Next,

genetic analyses revealed in unprecedented detail

the degree to which hybrids shared the DNA of

both parent species. And then crowd sourced data

drawn from eBird, a citizen-science project run

by the Cornell Lab, allowed the researchers to

expand the scale of the study and match bird

observations with winter temperatures.

 

The researchers analyzed blood samples from 167

chickadees-83 collected in 2000-2002 and 84 in

2010-2012. Using next-generation genetic

sequencing, they looked at more than 1,400

fragments of the birds' genomes to see how much

was Black-capped Chickadee DNA and how much was

Carolina.

 

The site that had been in the middle of the

hybrid zone at the start of the study was almost

pure Carolina Chickadees by the end. The next

site to the north, which Curry and his students

had originally picked as a stronghold of

Black-capped Chickadees, had become dominated by

hybrids.

 

Female Carolina Chickadees seem to be leading the

charge, Curry said. Field observations show that

females move on average about 0.6 mile between

where they're born and where they settle down.

That's about twice as far as males and almost

exactly as fast as the hybrid zone is moving.

 

As a final step, the researchers overlaid

temperature records on eBird sightings of hybrid

chickadees. They found a very close match:

hybrids occurred only in areas where the average

winter low temperature was between 14 and 20

degrees Fahrenheit. They also used eBird records

to estimate where the hybrid zone had been a

decade earlier, and found the same relationship

with temperature existed then, too. The only

difference was that those temperatures had

shifted to the north by about seven miles since

2000.

 

Chickadees-there are seven species in North

America-are fixtures in most of the backyards of

the continent. These tiny, fluffy birds with bold

black-and-white faces are favorite year-round

visitors to bird feeders, somehow surviving cold

winters despite weighing less than half an ounce.

 

To the untrained eye the Carolina Chickadee of

the southeastern U.S. is almost identical to the

more northern Black-capped Chickadee-although the

Carolina has a shorter tail, less white on its

shoulders, and a song of four notes instead of

two notes. Genetic research indicates the two

have been distinct species for at least 2.5

million years.

 

"The rapidity with which these changes are

happening is a big deal," Taylor said. "If we can

see it happening with chickadees, which are

pretty mobile, we should think more closely about

what's happening to other species. Small mammals,

insects, and definitely plants are probably

feeling these same pressures-they're just not as

able to move in response."