Saw the following on MDBirding but thought many of you would find it
fascinating. It was originally from Cornell but was posted on Maine Birds
Joe Coleman
From: Peter Vickery <petervickery@xxxxxxxxxxxxxx>
Subject: [Maine-birds] Black-capped and Carolina Chickadees shift their
ranges north - longish
Date: March 7, 2014 4:32:28 PM EST
To: Maine Birds <maine-birds@xxxxxxxxxxxxxxxx>
This from Cornell
Chickadees in poleward range shift
----------------------
Cornell University
PUBLIC RELEASE DATE:
6-Mar-2014
Contact: Joe Schwartz
Joe.Schwartz@xxxxxxxxxxx
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."
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