hen federal researchers
fitted a gray wolf in Oregon
with a radio-tracking collar,
they intended to report only
on the wolf ’s movements. A
little more than a month after
tracking began in the state’s
Mount Hood region, the signal went still. No one
can say for sure why the wolf died. It had not been
shot or poisoned. A necropsy done by the Oregon
State University Veterinary Diagnostic Lab found
no evidence of foul play. According to U.S. Fish and
Wildlife Service biologist John Stephenson, while
several things could have gone wrong for the wolf,
such as a paw injury that could have prevented it
from finding food, capture-related stress from the
radio-tracking collaring cannot be ruled out as the
possible killer. Capture myopathy is a condition of
animals in which overworked skeletal muscles (the
ones that fuel the fight-or-flight response to being
caught) start to break down and release a protein
that, in large amounts, can result in death.
In this context, stress is generally defined as the
physiological response to a stimulus (environmental
or psychological) that an individual (or animal) per-
ceives to be a threat. The stress response involves the
buildup of cortisol hormones and adrenaline, which
increases heart rate and blood pressure and even sup-
presses the immune system. When it’s chronic, stress
can be lethal, but stress also keeps animals safe.
“The stress response is about preparing the body
for a major expenditure of energy,” wrote Robert M.
Sapolsky, a neuroendocrinologist at Stanford Uni-
versity, in his seminal text Why Zebras Don’t Get Ul-
cers: The Acclaimed Guide to Stress, Stress- Related
Diseases, and Coping. Sapolsky argued that all an-
imals have essentially the same stress-response
mechanism, grounded in “fight-or-flight syndrome.”
Simply put, in the presence of danger, you have only
two choices: strike back or flee. From a physiologi-
cal perspective, regardless of which choice is acti-
vated, masses of energy are delivered to your mus-
cles. When a threat is perceived, the brain sends
signals through the autonomic nerves to the adre-
nal glands, which respond by pumping the hormone
epinephrine (adrenaline) into the bloodstream. The
heart begins to beat faster, blood rushes to the mus-
cles and other organs, and breathing becomes more
rapid. After the initial adrenaline surge subsides,
the adrenal glands begin to release cortisol until
the threat passes, at which point the nervous sys-
tem pumps the brakes on the stress response. In
humans, though, our awareness adds another level
of threat perception. Fear of danger can still linger;
therefore, the stress response can continue long after
the threat is eliminated. Animals, however, can turn
those thoughts off. “Zebras and lions may see trouble
coming in the next minute and mobilize a stress re-
sponse in anticipation,” Sapolsky writes. “But they
can’t get stressed about events far in the future.”THE GOOD, THE BAD AND THE FURBALLS
as researchers examine stress in the ani-
mal kingdom, they’re further clarifying the differ-
ences between short-term and long-term stress.
According to Aliza le Roux, a behavioral ecologist
conducting research on carnivores and primates in
South Africa, some experiments have shown posi-
tive effects of stress on lab rats. “Brief, acute stress
can actually lead to an increase in neurons in rats’
brains,” le Roux wrote in “What Animals Can Teach
Us About Stress” for The Conversation, an academic-
backed website that covers global issues. “And rats
who were stressed out as teenagers become more im-
pulsive as adults, which can make them more effec-
tive foragers, especially under high-risk conditions.”
We can all relate to a short-lived pressure boost-
ing our performance, but what about constant stress-
ors? According to le Roux, researchers are beginning
to uncover that data. “Studies on wild animals ap-
pear to confirm the idea that long-term, chronic
stressors can truly decrease your mental acuity,” she
wrote, pointing to a 2015 study that found that wild
guppies living in a stressful, polluted environment
made significantly more mistakes in cognitive chal-
lenges than guppies used to a more relaxed habitat.
Beyond cognitive deficiencies, long-term stress
and trauma can result in compulsiveness in ani-
mals. While disorders such as OCD and anxiety
are well documented in animals—such as Gus, the
neurotic polar bear who made headlines for com-
pulsively swimming figure eights in his pool (for
up to 12 hours) in New York’s Central Park Zoo—in
some cases the tic can evaporate once the stressor
is treated. Marinell Harriman, a rabbit rescuer and
rehabilitator and the author of House Rabbit Hand-
book: How to Live with an Urban Rabbit, has worked
with hundreds of the creatures over three decades.
“In caring for quite a few ‘sanctuary’ rabbits with
long- and short-term illnesses,” she writes, “we have