Life at the Zoo

by Phillip T. Robinson

  The physical examination of a patient traditionally begins as a hands-off exercise, observing first from a distance. Assessing the patient’s condition before it gets disturbed or excited is essential, whether it is a horse, a rhino, or a parrot, because clinical signs often quickly conceal themselves when an animal’s suspicions are aroused. In nature, the observer and judge is often a predator. Lameness mysteriously disappears and depression may be stoked with adrenalin, obscuring precious clues. The heightened awareness in a sick animal may be mistaken for normal vigilance. In our human experiences with doctors, the simple act of putting on a paper exam gown and removing our shoes and socks in the doctor’s office can make us puzzle about exactly where that pain was just ten minutes ago. When animals realize they are being watched, their antipredator radar switches on and camouflages many indicators that may be important clues to a problem. It may be necessary to revisit a patient several times and under different circumstances to obtain an unbiased impression of how an animal is acting. In the case of creatures that are particularly sensitive to strangers, entire reliance may have to be placed on the information of the animal keeper or video surveillance. An astute keeper is often the best judge of subtle changes that indicate illness—minute variations from the norm, such as diminished socialization, eye contact, mobility, appetite, or responsiveness.

  Most of the diseases of zoo animals are diseases caused by captivity, although many people expect exotic plagues from faraway places to be the norm. Several reviews of animal pathology cases involving thousands of zoo animal mortalities refute this notion and affirm that most diseases of zoo animals are relatively mundane. The annual medical report for the San Diego Zoo hospital in 1934 concluded: “The majority of our fatalities are preventable . . . [and] can be directly traced to poor sanitation and improper food handling.” Some thirty years ago, Chicago’s Brookfield Zoo veterinarian Dr. Joel Wallach determined that about 30–40 percent of zoo deaths were from diseases caused by bacteria, parasites, and viruses, and that the remaining 60–70 percent could be attributed to poor animal management and husbandry. The actual numbers are probably even worse, however, since infections often have their origins in stresses of various forms, which magnify the effects and opportunities for infectious and parasitic agents.

  Parasitism is widespread among nearly all forms of the world’s animal life, ranging from pesky skin infestations to microscopic malarial organisms that infect blood cells, and a mind-boggling variety of worms that migrate through body tissues, destroying cells and siphoning off protein and other nutrients from their hosts. A good parasite, like a good houseguest, is one that does not seriously trouble its host, at least not consistently. In other words, on a population basis, while the damage to the host does not ordinarily affect its survival as a species, it may occasionally have mortal consequences for individuals. This moderation is not because of benevolence on the part of parasites, but simply an evolutionary game in which the parasites that survive to reproduce tend not to destroy their primary domiciles, their animal hosts.

  The impact of parasitism within the confinement of the zoo depends on the organisms’ life cycles, as well as factors relating to sanitation. Most tapeworms, for example, require an intermediate host, such as an arthropod insect, to complete their life cycles; in the absence of arthropods in the zoo, the tapeworms’ cycle is short-circuited. I once received a call from an agitated curator who learned through the grapevine that I intended to release a bear from quarantine that was still testing positive for tapeworms. He was annoyed, fearing that this problem would become transmitted to the other bears that inhabited nearby enclosures. When I explained the parasite’s life cycle in detail and how transmission was not possible due to the lack of intermediate hosts, he realized that eating a bucket of tapeworms could not transmit the parasites.

  Parasites with more complex life cycles or with available co-conspirators can thrive in zoos under the proper conditions—the lungworm of sheep and goats is a good example. Snails, which are abundant in Southern California, are ideal intermediate hosts for the lungworm, Mulleria, which can cause chronic verminous pneumonia in its victims. Control of this parasite in exotic zoo goats has been achieved with specially medicated feeds and the control of its abundant intermediate hosts, common snails, with nontoxic, bubblegum-like sprays that glue the snails’ mouth parts shut when they feed on the treated vegetation, again short-circuiting the parasite’s life cycle.

  Parasites with direct life cycles require no third-party transaction for transmission, or even a transition stage in the environment prior to reinfestation. These have a propensity to produce heavy parasite burdens in confined animals because the eggs passed into the environment can cause reinfestation with adult worms in the absence of an intermediate host organism. Regular worming programs may be important in confined animals to prevent parasite damage to hosts tissues and the loss of nutrients that result. Small parrots in the zoo are particularly prone to roundworm infections of this type from Ascaridia and require regular monitoring, deworming, and husbandry measures that reduce fecal contamination of their feed. (Don’t put their feed pans under their perches!)

  In one major zoo, a tragic parasite problem occurred when gorillas and South American bush dogs alternately shared a grassy exercise area. Unbeknownst to the medical staff, these carnivores were infested with a type of tapeworm that produces destructive parasitic cysts in the major internal organs of some species. The gorillas became contaminated with the infective tapeworm forms by playing on the bush dog–soiled grass, and they developed massive parasite cysts in their livers and abdominal cavities. Unfortunately, no effective treatment was available, and an entire group of valuable breeding animals perished from the infestations.

  Tapeworm life cycle in a zoo bear

  Wild animals frequently recover from a wide variety of infections and injuries during their lifetimes, although any serious injury can make an individual much more vulnerable to death from predation. Some insightful studies have been done by the examination the skeletons of wildlife that have been collected for museums in various parts of the world, revealing a wide range of dental and skeletal diseases that animals must have experienced for extended periods of time. Primates in one study had arthritis and healed fractures of arms, legs, fingers, and toes. Of all the primates examined, the group with an astonishingly high rate of healed fractures of arms was the gibbons, which are highly arboreal in habit, swinging dramatically between tree branches. Fortunately for early zoo veterinarians, many animals healed from their injuries despite their lack of medical treatment. Dental disease, such as tooth abscesses and fractures, has also been found to occur in many primate species, but more particularly in wild apes, especially older individuals. Not surprisingly, comparisons with zoo apes revealed that dental decay is much more common in captive animals than in their wild counterparts, suggesting shortcomings in diet, behavior, or environment.

  As animals age in the wild, the loss of dental competency limits their lifespan. Wild Weddell seals, for example, live under large ice packs in the Antarctic and survive far from open water by maintaining open breathing holes through the ice, gnawing them clear with their teeth. A study on the longevity of this species revealed that aging Weddell seals whose teeth had worn down could no longer perform this task, so the durability of their teeth ultimately determined how long they lived before they suffocated under the ice.

  Wild elephants also have their life spans limited by their teeth, which give out after around sixty-five years, should they survive other life challenges. As with human statistics, most animal longevity records far exceed the average lifespan; the maximum recorded for a captive elephant is around seventy years. Over an elephant’s lifespan it has six sets of molar-like teeth (premolars and molars), which erupt, one by one, in single file, from the rear of the jaw and migrate forward in a line as they wear over the years. No more than two molar-like teeth are ordinarily present in each dental quadrant at any given time, and they appear so
mewhat like glued together stacks of poker chips lying on their sides. Gradually, they break apart in flakes at the front of the jaws and are shed in fragments, as if they were dropping off the end of a conveyor belt. When the last molar is expended and food can no longer be chewed, elephants rapidly start to lose body condition from malnutrition. In captivity, aging elephants can be fed special diets if chewing food becomes a limiting factor.

  In general, animals in captivity live significantly longer than their wild counterparts. The reasons include the absence of several major mortality denominators, such as predation and food supply, not to mention the availability of veterinary care.

  There is a millionfold difference in the weight of a pygmy shrew (2–3 grams) vs. a 5,000 kilogram elephant. The energy costs of being small are huge, particularly when we view the problem in terms of “metabolic body size,” which correlates metabolism to body surface area rather than weight. Smaller animals have larger surface areas in relationship to weight than do larger ones, causing more rapid energy losses by the radiation of body heat. Other factors, however, including behavior, climate, food gathering costs, and the energy costs of locomotion, factor into the energy economy of a free-living animal. In the zoo, small animals have narrowed options for energy conservation and less ability to select high energy foods. The negative consequences of small body size make them particularly vulnerable in confinement, while larger animals generally allow greater margins for error in captivity. Shrews can live twice as long in captivity as in nature with competent husbandry, although in the wild they rarely live longer than a year. Imagine the pressure that this puts on a species to complete its entire existence on earth in less than 365 days. By then they have been parents and grandparents, racing through life like hairy little comets (their normal body temperature is a toasty 105° F). Short childhoods and gestations, serial mates and pregnancies, and early senescence—before a human can even have a memorable thought, a shrew is history.

  Several years ago a New York Times article concluded that “as animals get bigger, from the tiny shrew to huge blue whale, pulse rates slow down and life spans stretch out longer, conspiring so that the number of heartbeats during a stay on Earth tends to be roughly the same—around a billion.” If this is truly the case, we should all do everything possible to use our (and our zoo animals’) heartbeats in an economical fashion and avoid unnecessary stresses that raise heart rate, especially those that provide little pleasure. More philosophically, comedian George Carlin once observed: “Life is not measured by the number of breaths we take, but by the moments that take our breath away.” If we are going to splurge and consume this limited resource, perhaps it might better be spent downhill skiing, surfing, riding a motorcycle, or doing conservation research in a war zone instead of worrying about trivial things in life over which we have little control. We all probably know people who live their entire lives by this philosophy. My dog figured this out a long time ago.

  Philosophers like George Carlin consider longevity in relative terms where qualitative rather than quantitative measures are employed. Whenever a person dies prematurely, there is usually a particularly acute sense of loss, and a feeling that the deceased was cheated out of his or her fair share of life’s temporal entitlements. Those left behind often rationalize this circumstance by pointing out the “quality” of the decedent’s life. This probably helps the survivors to cope with the injustice and the inexplicability of their own mortal existences. Life, like zoo medical practice, seems meant to be experienced looking forward and understood looking backward, which is why most medical textbooks tend to be constructed by analyzing our failed experiences with the dead and dying.

  Livestock businesses, professional sports, and many corporate enterprises define longevity in terms of productivity. Nature, however, operates exclusively within the productivity model of longevity—scientists usually call it “natural selection.” Agriculturalists have made a quantitative science of productivity in the poultry, livestock, and milk industries. With dairy cows, it is referred to as the “Duration of Productive Life” or “DPL”—the ability of a cow to remain in a herd based on her capacity to produce profitable quantities of milk. The public expectations of zoos, however, differ radically from agricultural and nature models: zoos are now often expected to provide for their animals from cradle to grave without regard to DPL. In many zoos, the productive life of an animal has been defined by how long it is suitable for public exhibition or breeding. Where do all of the surplus babies go? What becomes of the tiger that no longer fits into the group, or is not presentable for exhibition? In response to part of this problem—unplanned parenthood—the Contraception Advisory Group, comprising zoo curators, veterinarians, and reproductive physiologists, was formed in 1989. In 1999, the American Zoo and Aquarium Association established the Contraception Center at the St. Louis Zoo, where the CAG is now based. It currently provides advice on thirty different birth control methods, in addition to the oldest and most reliable method of all—abstention.

  Zoo veterinarians probably have the ultimate form of house call practices. This yesteryear style of medicine provided chances to see patients undisturbed in their home environments. Farmers and horse owners have long benefited from this ambulatory sort of veterinary practice, although it is now gaining ground in small animal veterinary medicine as well. In some respects, the old-fashioned human house call was on the cutting edge, but now it has been replaced by impersonal managed care systems. Human medical practices (and veterinary practices too) seem to have forgotten the value of making good, clean, firsthand observations, but instead require their patients to run the gauntlet of the waiting room and the nurse long before making that first eye contact with their physician. By the time you reach the doctor’s office and the blood pressure cuff goes on your arm, what are they measuring—your vital signs, or the stress of traffic and the doctor’s office? When, and if, they check your blood pressure at both the beginning and the end of your office visit, the second measurement is almost invariably lower. Doctors call this scenario “white coat hypertension.” Medical offices, human and animal, don’t always bring out the best in either the doctor or the patient. There is an inherent confusion that springs from ringing phones, multitasking, and concerns about insurance copayments.

  Our domestic dogs and cats take bumpy rides in the family car before being presented for veterinary treatment. The mere act of bringing out the pet carrier at home is enough to send some pets into hiding under the nearest piece of furniture. Some pets go with enthusiasm for a ride in the car but panic at the sight or smell of the animal clinic. In an ideal world, human patients should be seen as they live daily on their own turf and without the side effects of traveling through miles of hectic traffic, scrambling in from the parking garage and whooshing up six floors in an elevator to a place that smells like a doctor’s office. Zoo doctors still make house calls.

  Field biologists who research and observe animal behavior continually strive to devise methods of keeping their presence from affecting their observations of animals. An observer is seldom invisible or totally unobtrusive, and some of the study methods have to be a bit contrived. One always has to question the effect of an observer’s physical presence on the behavior of the observed—including that of the late Diane Fossey, sprawled in a patch of nettles with her Gorillas in the Mist, and of Jane Goodall, camped out in Gombe Stream Reserve in her Life with the Chimpanzees.

  Dr. Goodall—who, like Fossey, seems to prefer socializing with animals than with her fellow humans—pioneered her techniques in chimps by allowing them to habituate to her presence. Slowly and patiently, she made contact with the chimps in the forest, hoping that they would begin to accept her as they would a harmless bird on a branch. One day she allowed herself to touch a chimp, and the rest is history that you can read about in National Geographic. Like a news reporter covering breaking events in volatile parts of the world, the effects of the participant-observer on real events is always a lingering questio
n. Goodall’s work took enormous commitment and patience, and she probably thinks of herself, in many ways, as more akin to chimps than to humans, a conclusion her students would not dispute.

  Some years ago, I was invited to a small meeting with Dr. Goodall at the National Geographic Society headquarters in Washington to discuss a proposed plan for a West African chimpanzee reserve where retired research subjects could live out the rest of their lives in semicaptivity. Because she is an enormous icon in the animal world, people treat Dr. Goodall with great courtesy and reverence. When, in the course of our discussions about chimpanzees, I innocently referred to them as “animals,” her face flushed, and she admonished me: “They are chimpanzees, not animals! I prefer to refer to them as ‘chimp beings,’ just like we call people ‘human beings.’” I then realized just how passionately she identified with them, and while verbally groping to acknowledge her sincerity, I inadvertently used the “A” word again. My African friend sitting next to me radiated a horrified look as if I had accidentally dropped a soiled handkerchief into Dr. Jane’s soup bowl and implored, in a whisper, “She doesn’t like it when you call them animals!”

  I don’t think that Dr. Goodall is naive enough to believe that the presence of people does not interfere in some manner with the behavior of her chimpanzees, and, after all, many astonishing things have been learned from her studies that forever changed the way that the world views chimpanzees. Presuming to be to be an unobtrusive observer would be a bit of an exaggeration, however, since she did offer bananas as bribes to gain their ongoing trust and cooperation. Jane became a sort of banana goddess who brought fruit to their forest—fruit, in fact, that wasn’t even African, but had originated in South America. Behaviorists call this study method “provisioning,” a sort of icebreaking and sustaining technique for narrowing the human/animal distance. Some have quietly criticized the advantage that she took of the chimps’ weakness for bananas and privately call her Gombe study site in Tanzania her “Banana Republic.” This Third World reference is somewhat deserved, inasmuch as competition for the bananas apparently became abusive and undemocratic at times. Some chimps even traded bananas for sexual favors, while others simply hoarded them. Rarely did the “chimp beings” exhibit more high-minded communal benevolence when it came to their food. In the end, it is difficult to know what effect this method had on their normal behavior. If nothing else, their actions bolster Dr. Jane’s contentions that chimpanzees are, indeed, very much like people—complete with such unpleasant characteristics as greed.