This article appeared in the most recent Cornell Labortory of Ornithology
newsletter. Seems to fit well with some recent posts.
Warming Temperatures Are Pushing Two Chickadee Species—and Their
By victoriaon Thursday, March 6th, 2014 - 8 Comments
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 was published 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.”
The two chickadee species meet and hybridize in a narrow zone that has shifted
northward 7 miles in the last decade.
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 crowdsourced 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 crowdsourced 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
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 a map of the
region of overlap between the two species, created from eBird sightings. They
found a very close match: the zone of overlap 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 overlap 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.
On Saturday, March 22, 2014 10:46:52 AM, colin trainor <>
The Supplementary material with bird lists is available here:
Most of the species are resident/sedentary birds with small territories - some
of the frugivores and nectarivores/raptors are capable of moving widely.
Seasonality - the study area is very close to the Equator (4-6 degrees South),
I suspect that there is zero seasonal climate diffs (ie no season/aseasonal)
and very limited rainfall seasonality (ie everwet, or close to).
> Date: Sat, 22 Mar 2014 18:55:03 +1100
> Subject: Re: [Birding-Aus] Rapid upslope shifts in New Guinean birds
> illustrate strong distributional responses of tropical montane species to
> global warming
> The study does not appear to consider seasonal changes that are more
> likely than small distribution movements due to climate shifts.
> colin trainor wrote:
> >An interesting recent study that re-samples sites first surveyed by Jared
> >Diamond 40+yrs ago.... to look at changes in elevation use by montane birds
> >in New Guinea region..
> >Temperate-zone species have responded to warming temperatures by
> >shifting their distributions poleward and upslope. Thermal
> > tolerance data suggests that tropical
> >species may respond to warming temperatures even more strongly than
> >temperate-zone species,
> > but this prediction has yet to be tested.
> >We addressed this data gap by conducting resurveys to measure
> >distributional responses
> > to temperature increases in the
> >elevational limits of the avifaunas of two geographically and faunally
> >independent New Guinean
> > mountains, Mt. Karimui and Karkar Island,
> >47 and 44 y after they were originally surveyed. Although species
> >richness is roughly
> > five times greater on mainland Mt. Karimui
> > than oceanic Karkar Island, distributional shifts at both sites were
> >similar: upslope
> > shifts averaged 113 m (Mt. Karimui) and
> >152 m (Karkar Island) for upper limits and 95 m (Mt. Karimui) and 123 m
> >(Karkar Island)
> > for lower limits. We incorporated these
> >results into a metaanalysis to compare distributional responses of
> >tropical species
> > with those of temperate-zone species,
> >finding that average upslope shifts in tropical montane species match
> >local temperature
> > increases significantly more closely than
> >in temperate-zone montane species. That tropical species appear to be
> >strong responders
> > has global conservation implications and
> >provides empirical support to hitherto untested models that predict
> >widespread extinctions
> > in upper-elevation tropical endemics with
> >small ranges.
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