Bird
populations responding to climate change
University
of Utah
With puzzling variability, vast numbers of birds from Canada’s boreal forests migrate hundreds or thousands of miles south from their usual winter range. These so-called irruptions were first noticed by birdwatchers decades ago, but the driving factors have never been fully explained.
Now scientists have pinpointed
the climate pattern that likely sets the stage for irruptions – a discovery
that could make it possible to predict the events more than a year in advance.
The
researchers found that persistent shifts in rainfall and temperature drive
boom-and-bust cycles in forest seed production, which in turn drive the mass
migrations of pine siskins, the most widespread and visible of the irruptive
migrants. “It’s a chain reaction from climate to seeds to birds,” says
atmospheric scientist Court Strong, an assistant professor at the
University of Utah and lead author of the study.
Many seed-eating boreal species are subject to irruptions, including Bohemian and cedar waxwings, boreal chickadees, red and white-winged crossbills, purple finches, pine and evening grosbeaks, red-breasted nuthatches, and common and hoary redpolls. The authors focused on the pine siskin, a species featured prominently in earlier work on irruptive migrations.
Previous
studies have found evidence that irruptions are triggered by food shortages
caused by the large-scale collapse of seed production in northern pine, spruce
and fir forests.
“We’ve
known for a long time that weather was probably important, but prior analyses
by ecologists have been unable to identify exactly what role weather was
playing in this phenomenon,” says ecologist Walt Koenig, a senior scientist at
the Cornell Lab of Ornithology and co-author of the new study incorporating climate
science. “It’s a good example of the value of interdisciplinary work,” Koenig
says.
To
resolve the question, the scientists turned to a remarkable trove of data
gathered by backyard birders as part of Project FeederWatch, a citizen science
initiative run by the Cornell Lab of Ornithology.
FeederWatcher volunteers
systematically record bird sightings from November through early April and
they gave the scientists more than two million observations of pine siskins
since 1989. The crowd-sourced data makes it possible to track the movement of
bird populations at a continent-wide scale.
Read
more at University of
Utah.