2019-07-01_Discover

56 DISCOVERMAGAZINE.COM

STRESS

EVERYTHING

WORTH

KNOWING

As with people,

excess stress can

cause pathological

disorders in animals

— even pampered

pets. In a recent survey

of over 4,000 dog owners,

stress symptoms were reported

in almost half the canines. “It’s the

most common reason for dogs to act

out,” explains study leader Nicholas

Dodman, a veterinary behaviorist

at the Center for Canine Behavior

Studies in Salisbury, Connecticut.

Canines show stress overtly —

whimpering, quivering, escape

attempts — and internally

through increases in blood

pressure, heart rate and cortisol

levels. The symptoms may be

acute, triggered by particular events like vet visits, and alleviated after-

ward. But other causes are more pernicious. Some dogs, for example,

experience separation anxiety when left home alone. While roughly

15 percent make their distress known with howls, torn-up sofas and

accidents, studies using hidden cameras and hormone monitoring

suggest many more are afflicted. “They just

shrink into themselves and kind of enter a

state almost bordering on depression that

lasts as long as the separation,” says Dodman.

Zoo animals can experience stress, too.

Although they’re well-fed and safe from

predators, captivity can cause chronic stress

that negatively impacts growth, immunity

and reproduction. And many perform

seemingly pointless, repetitive actions that

sometimes result in self-harm. For example,

walruses rub their tusks against concrete

pool edges, parrots pluck out feathers, and

bears pace compulsively. The behaviors

exaggerate what animals would do in nature,

including hunting and roaming over vast ter-

ritories. Analyzing 23 species, a 2016 Animal Behavior paper showed

the farther wild carnivores travel on a daily basis, the more time their

captive counterparts — “in an unnatural situation of confinement

and stress and boredom,” says Dodman — spent performing these

potentially harmful behaviors.

Stress

Across

Species

Physicists and engineers often define stress as force

acting on a certain area. Too much makes an object

budge, bend or break. The result could be as trivial as

a snapped pencil or as catastrophic as a bridge collapse.

Directly observing stress is tricky — in most cases,

researchers end up measuring it in the aftermath.

But we’d prefer to know how much stress a struc-

ture can withstand before it succumbs to it — or is

even built. Zoomed out, things may seem stable,

while at a finer scale there are “all these places where

stresses are accumulating,” says Emanuela Del Gado,

a physicist at Georgetown University. It’s “a magic

combination of stresses acting in different directions

that cancel each other.” But when an outside force

comes along, say a strong wind or heavy load, “that

magic combination can be lost,” she says, and the

structure will fail. To prevent this, Del Gado and oth-

ers study how materials handle stress using computer

simulations and mathematical models.

Engineering

and Design

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