How Does Captivity Affect Wild Animals?
Most experts agree it depends on the species, but much evidence shows large mammals
suffer under even the best human care.
By Cody Cottier, Discover Magazine, Aug 7, 2021 10:00 PM
For much of the past year and a half, many of us felt like captives. Confined mostly within
monotonous walls, unable to act out our full range of natural behavior, we suffered from
stress and anxiety on a massive scale. In other words, says Bob Jacobs, a neuroscientist at
Colorado College, the pandemic gave us a brief taste of life as lived by many animals.
Though anthropomorphism is always suspect, Jacobs observes that “some humans were
quite frustrated by all that.” This is no surprise — we understand the strain of captivity as
we experience it. But how do animals fare under the same circumstances? Putting aside the
billions of domesticated livestock around the world, some 800,000 wild or captive-born
animals reside in accredited American zoos and aquariums alone. Many people cherish
these institutions, many abhor them. All want to know: Are the creatures inside happy?
Signs of Stress
Happiness is hard to judge empirically, but scientists do attempt to quantify welfare by
measuring chronic stress, which can arise as a result of restricted movement, contact with
humans and many other factors. The condition reveals itself through high concentrations of
stress hormones in an animal's blood. These hormones, called glucocorticoids, have been
correlated with everything from hair loss in polar bears to reproductive failure in black
rhinos.
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That said, it’s difficult to say what a normal level of stress is for any given animal. An obvious
baseline is the captive’s wild counterpart (which surely has its own troubles, from predation
to starvation). But the problem, says Michael Romero, a biologist at Tufts University, “is that
there’s just not enough data.” Given the challenge of measuring a wild animal’s stress — the
requisite capture isn’t exactly calming — few such studies have been undertaken, especially
on large animals.
Besides, hormones may be an imperfect gauge of how agitated an animal really feels.
“Stress is so complicated,” Romero says. “It’s not as well characterized as people think.” So
researchers can also look for its more visible side effects. Chronic stress weakens the
immune system, for example, leading to higher disease rates in many animals. Opportunistic
fungal infections are the leading cause of death in captive Humboldt penguins, and perhaps
40 percent of captive African elephants suffer from obesity, which in turn increases their
risk of heart disease and arthritis.
Another sign of stress is decline in reproduction, which explains why it’s often difficult to get
animals to breed in captivity. Libido and fertility plummet in cheetahs and white rhinos, to
name two. (A related phenomenon may exist in humans, Romero notes: Some research
suggests that stress, even when breeding does succeed, high infant mortality rates plague
some species, and many animals that reach adulthood die far younger than they would in
the wild. The trend is especially poignant in orcas — according to one study, they survive
just 12 years on average in American zoos; males in the wild typically live 30 years, and
females 50.
Big Brains, Big Needs
Our wild charges don’t all suffer so greatly. Even in the above species there seems to be
some variability among individuals, and others seem quite comfortable in human custody.
“Captive animals are often healthier, longer-lived and more fecund,” writes Georgia Mason,
a behavioral biologist at the University of Ontario. “But for some species the opposite is
true.” anxiety and depression can reduce fertility.)
Romero emphasized the same point in a 2019 paper: the effect of captivity is, ultimately,
“highly species-specific.” In many ways it depends on the complexity of each species’ brain
and social structure. One decent rule of thumb is that the larger the animal, the worse it will
adjust to captivity. Thus the elephant and the cetacean (whales, dolphins and porpoises)
have become the poster children of the welfare movement for zoo animals.
Jacobs, who studies the brains of elephants, cetaceans and other large mammals, has
described the caging of these creatures as a form of “neural cruelty.” He admits they are
“not the easiest to study at the neural level” — you can’t cram a pachyderm into an MRI
machine. But he isn’t bothered by this dearth of data. In its absence, he holds up
evolutionary continuity: the idea that humans share certain basic features, to some degree,
with all living organisms. “We accept that there’s a parallel between a dolphin’s flipper and
the human hand, or the elephant’s foot and a primate’s foot,” Jacobs says.
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Likewise, if the brain structures that control stress in humans bear a deep resemblance to
the same structures in zoo chimps — or elephants, or dolphins — then it stands to reason
that the neurological response to captivity in those animals will be somewhat the same as
our own. That, Jacobs says, is borne out by a half century of research into how impoverished
environments alter the brains of species as varied as rats and primates.
Abnormal Behavior
Not all forms of captivity are equally impoverished, of course. Zookeepers often talk about
“enrichment.” Besides meeting an animal’s basic material needs, they strive to make its
enclosure engaging, to give it the space it needs to carry out its natural routines. Today’s
American zoos generally represent a vast improvement over those of yesteryear. But animal
advocates contend they will always fall short of at least the large animals’ needs. “No matter
what zoos do,” Jacobs says, “they can’t provide them with an adequate, stimulating natural
environment.”
If there is any doubt as to a captive animal’s wellbeing, even the uninformed zoogoer can
detect what are perhaps the best clues: stereotypies. These repetitive, purposeless
movements and sounds are the hallmark of a stressed animal. Elephants sway from side to
side, orcas grind their teeth to pulp against concrete walls. Big cats and bears pace back and
forth along the boundaries of their enclosures. One survey found that 80 percent of giraffes
and okapis exhibit at least one stereotypic behavior. “Stress might be hard to measure,”
Jacobs says, “but stereotypies are not hard to measure.”
Proponents are quick to point out that zoos convert people into conservationists, and
occasionally reintroduce endangered species to the wild (though critics question how
effective they truly are on these fronts). Considering their potential to bolster the broader
conservation movement, Romero suggests an ethical calculation might be in order. “Maybe
sacrificing a few animals’ health is worth it,” he says.
Wherever these moral arguments lead, Jacobs argues that “the evidence is becoming
overwhelming” — large mammals, or at least many of them, cannot prosper in
confinement. The environmental writer Emma Marris concludes the same in Wild Souls:
Freedom and Flourishing in the Non-Human World. “In many modern zoos, animals are well
cared for, healthy and probably, for many species, content,” she writes, adding that
zookeepers are not “mustache-twirling villains.” Nevertheless, by endlessly rocking and
bobbing, by gnawing on bars and pulling their hair, “many animals clearly show us that they
do not enjoy captivity.”
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