A Bird's-Eye View of Climate Change
Computer modeling predicts dramatic shifts in species' ranges
Chickadees, song sparrows, robins
and other common bird species are among the familiar sights and sounds
of Maine and much of the eastern United States, but in a world affected
by a changing climate, they may not always be around.
"Both climate and landscape are important to birds," says Steve
Matthews, who, for his master's degree in wildlife ecology at the
University of Maine, studied how bird species might respond to a warmer
world.
Matthews worked with UMaine Professor Raymond O'Connor on a computer
model using current information about climate and the eastern U.S.
landscape to show where bird species occur. Bird density is hard to
measure directly; the researchers used incidence, a measure of how
reliably a species can be found at a location.
O'Connor's research focuses on the consequences of changing landscapes
and agricultural practices on birds and other wildlife in Great Britain
and North America.
Using current data about climate, vegetation and elevation, the
researchers found that their model faithfully reproduced the known
ranges of 150 bird species. But the model wasn't perfect, says Matthews,
a native of Charlottesville, Va. For most of 36 other species, the model
did a poor job of reflecting current knowledge. Nevertheless, success
with a large number of species meant the computer model had accurately
captured factors critical to those species.
Matthews and O'Connor then turned to the future. One of the aces in
their hand was a recent study of how eastern forests might change in a
world made warmer by increasing greenhouse gases in the atmosphere. That
work by two U.S. Forest Service scientists, Louis Iverson and Anantha
Prasad of the Northeastern Research Station, paved the way for Matthews
and O'Connor to look at the consequences for birds.
Using the 150 bird species for which
they had reliable information, the UMaine scientists built the forest
data into their own models. They also used two climate change scenarios,
one from the Hadley Centre for Climate Prediction and Research in
England, and one from the Canadian Centre for Climate Modelling and
Analysis (CCCma). When they ran their model for each of the 150 species,
the results surprised Matthews, who had worked on ornithology research
projects in the mid-Atlantic states and the South before he came to New
England.
"More than half the species were projected to lose at least 25 percent
of their current abundance in the eastern U.S. That's a lot; a big
surprise. It doesn't mean that they would go extinct. Many would
probably increase their range in Canada, but we'll lose them in large
parts of the U.S.," Matthews says.
The most significant changes occurred in the southern portions of birds'
ranges. In some cases, the model suggested that certain birds would
disappear altogether from that portion of their current range. In other
cases, a species might change from being abundant in an area to being
rare. The results also showed that a small number of species would
increase their ranges.
"Many bird species are limited in their distribution by climatic
constraints and by their habitat, such as where a particular type of
forest is located," says O'Connor. "We were able to work out where and
in what numbers each bird species would survive for the eastern U.S. — a
first in climate change studies. Previous work considered only the
climate envelope, not the joint effects of shifting habitat (forest) and
shifting climate."
Among the species projected to become less abundant across the East are
Maine's state bird, the black-capped chickadee (Parus atricapillus), the
song sparrow (Melospiza melodia) and the American robin (Turdus
migratorius). In Maine itself, the model estimates that black-capped
chickadees and robins are likely to see little change, while song
sparrows could decline significantly.
Predicting the future, even with the most up-to-date information, is
always tricky. Whether bird species actually shift their ranges in the
future as the UMaine model suggests depends on climate and biology. If
climate changes as the Hadley and Canadian climate models suggest, and
if the birds maintain their present relationship to climate and habitat,
then the UMaine model results may come to pass.
"The uncertainty is about the exact pattern of climate change (Hadley
and CCCma are extremes) and whether the birds might adapt to change in
ways they do not now display, such as by changing their temperature
tolerances or by turning to other new (habitat) types in which to nest,"
says O'Connor.
The Forest Service has published the research on trees by Iverson and
Prasad and posted it on the Web.
http://www.fs.fed.us/ne/delaware/atlas/index.html
In October, the Forest Service also
published UMaine's bird species maps in Atlas of Climate Change Effects
on Common Birds in the Eastern United States. Funding for the atlas
included support from UMaine's Office of the Vice President for Research
and the College of Natural Sciences, Forestry, and Agriculture.
Matthews' research received financial support from the Forest Service
and the Department of Wildlife Ecology at UMaine. He is now a Ph.D.
student at Ohio State University studying the ecology of migration in
birds.
by Nick Houtman
January-February, 2005
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