Projected increases in the
frequency, intensity and duration of heatwaves in the desert of the
southwestern United States are putting songbirds at greater risk for death by
dehydration and mass die-offs, according to a new study.
Researchers used hourly temperature
maps and other data produced by the North American Land Data Assimilation
System (NLDAS) -- a land-surface modeling effort maintained by NASA and other
organizations -- a long with physiological data to investigate how rates of
evaporative water loss in response to high temperatures varied among five bird
species with differing body masses. Using this data, they were able to map the
potential effects of current and future heat waves on lethal dehydration risk
for songbirds in the Southwest and how rapidly dehydration can occur in each
species.
Researchers homed in on five
songbird species commonly found in the desert southwest: Lesser Goldfinch,
House Finch, Cactus Wren, Abert's Towhee and the Curve-billed Thrasher.
Under projected conditions where
temperatures increase by 4 degrees Celsius (7 degrees Fahrenheit), which is in
line with some scenarios for summer warming by the end of the century,
heatwaves will occur more often, become hotter, and expand in geographic range
to the point where all five species will be at greater risk for lethal
dehydration.
Birds are susceptible to heat
stress in two ways, said co-author Blair Wolf, a professor of biology at the
University of New Mexico. With funding from the National Science Foundation,
Wolf investigated heat tolerance for each of the five species in the study as
well as for other bird species in Australia and South Africa. "When it's
really hot, they simply can't evaporate enough water to stay cool, so they
overheat and die of heat stroke," he said. "In other cases, the high
rates of evaporative water loss needed to stay cool deplete their body water
pools to lethal levels and birds die of dehydration. This is the stressor we
focused on in this study."
What happens is at about 40
degrees Celsius [104 degrees Fahrenheit], these songbirds start panting, which
increases the rate of water loss very rapidly, explained co-author Alexander
Gerson, an assistant professor of biology at the University of
Massachusetts-Amherst. At the time of the study, he worked with Wolf as a
postdoctoral researcher at the University of New Mexico. He added, "Most
animals can only tolerate water losses that result in 15 or 20 percent loss of
body mass before they die. So an animal experiencing peak temperatures during a
hot summer day, with no access to water, isn't going to make it more than a few
hours."
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