Life at the Zoo

by Phillip T. Robinson

  One of the best ways to bring home this message about animal microenvironments is to actually put oneself in the animals’ places. Spend the night where the bears sleep and see if you can get a good night’s rest on a cement floor. I once suggested that to a keeper who resisted the use of straw bedding and to an administrator who resisted supplementary heat. Many people would be surprised at how intolerably cold and miserably uncomfortable it is to camp out on bare concrete without other heat sources, and how quickly a chill sets in as the sun moves away from an exhibit, leaving animals in involuntary shade. You or I would move a few yards into the sun if we were sitting in a city park, or we would slip on a sweater or jacket.

  Each zoo has its own unique set of microclimates, and all animals fare appreciably better if given effective protection from the prevailing wind, particularly in combination with a substrate that conserves body heat and pads them from hard surfaces. The effects of these seemingly trivial matters of husbandry are always underestimated and underutilized, perhaps even more so in milder climates than places where there is a strong annual cycle that profoundly reminds humans of seasonal changes. Keepers sometimes referred to me, discreetly, as “Dr. Bedding” because of my nagging insistence that animals be provided with softer, warmer surfaces to rest on in their enclosures. I always took this as a compliment rather than as an insult. One of the simplest, most immediate, ways to provide warmth is to offer dry straw or wood shavings as an option to dirt or concrete. We gave the great apes burlap sacks to make nests with, and some proceeded to decorate themselves Sadie Hawkins–style by fashioning their own versions of burlap hats and shawls.

  When safely installed, useful heat-producing devices include infrared heat lamps, gas radiant heaters, electrically heated rocks, and warm resting platforms. There is no mistaking how animals appreciate these small appliances, huddling on or near them during inclement weather. The older or younger the animal, the more beneficial supplemental heat is. The zoo’s red kangaroos and wallabies, which lived on a slope with unfavorable sun and draft exposures, responded dramatically to the addition of heat lamps, bedding areas, and windbreaks. Before we made these simple improvements, many marsupials had chronic problems with weight loss and foot and tail infections, and they often lost their pouch babies because of the cascade of problems induced by the stress of cold and dampness. The numbers of ill and infirm animals dropped dramatically in some groups with just several simple heat-conserving changes to their husbandry.

  For semiaquatic and aquatic species, water temperature affects behavior greatly, and some animals avoid water altogether when temperatures are allowed to drop too low. Hippos, in particular, dislike frigid water and spend more time languishing outside their pools, even though they prefer to be in water most of the day. Hippo births were also more successful when the babies got the extra help of just a few degrees rise in water temperature, since they are born directly in the water. They have to make the shocking transition from 100° F inside the mother’s uterus to the chill of a water pool. They emerge like a basketball that has been released by a submarine and pop to the surface, dragging their umbilical cords like rope tethers. Pygmy hippos simply stay out of cold water altogether, and, unlike their larger relatives, give birth on land.

  Social interactions between animals should be monitored continuously in exhibits, for not all animals appreciate company, and some become extremely aggressive when they encounter strange cagemates. Bringing new individuals into existing social groups is a common cause of trauma in zoos. Zoo veterinarians expend a disproportionate amount of time in the case of primates, which are particularly prone to social discord of this type. Carelessly planned and executed introductions to one another greatly increase the likelihood of serious injury. In order to avoid aggression and excess competition for resources, it is often necessary to provide for redundancy in cage furniture, resting places, feeding stations, and water supplies. Sight barriers that permit an animal to retreat from the stares of edgy companions can lower tensions and avoid antagonism and trauma. The adage “out of sight, out of mind” works in many introduction strategies.

  Most newly arrived zoo animals undergo a period of quarantine in the zoo in a location separate from the exhibit area. During this two- to four-week period, physical examinations, medical observation, tuberculosis testing, blood studies, and parasite screening establish known baselines before the animals take up zoo residency. Social contact with their new group is seldom possible during this period. Primates are among the most sensitive species in this adaptation process. Since the new arrival is at a social disadvantage to the resident inhabitants, special care must be taken to introduce the new animals to established ones gradually. Placing the new arrival in visual, auditory, and olfactory range of its new companions while keeping it physically separated is typically the first step. This is followed by allowing the new animal a solo adventure into the new exhibit to explore and learn the novel territory. A third phase may permit limited physical contact of the newcomer with more benign members of the group, and then full contact with selected individuals in attempts to establish a mentor or buddy system. The final step is the integration of the entire group, often by adding the most volatile member last, when the newcomer is already functioning in the exhibit area. By contrast, “cold turkey” (“hard”) kinds of introductions are done out of ignorance, impatience, or carelessness and frequently causes injuries or even deaths. The temporary removal of an individual for hospital treatment may disrupt social relationships enough to require a careful reintroduction protocol in some cases.

  Sequential (“soft”) introduction techniques provide the best prospects for success in most zoo animals. This often employs the psychology of “home court” advantage, similar to the strategy used by lion and tiger trainers in circuses. The trainer always enters the cage first, establishing a psychological territorial advantage over the lions and tigers, which are then funneled into the show cage for the performance. Similarly, depriving the established alpha monkey of such leverage in a zoo exhibit tends to reduce the impact of this first physical encounter with a newly introduced animal and allows more social latitude for the integration of the newcomer. On the fateful day of direct contact, other techniques, such as overprovisioning with foods or unfamiliar furnishings (for example, straw or hay bedding) can provide useful diversions and lessen the possibilities of conflict.

  Despite extensive introductory efforts, a pair of giant pandas in the San Diego Zoo was never able to get along compatibly enough to breed, which led to the program for artificial insemination that succeeded in producing a baby in the year 1999. Some species do not tolerate the ongoing presence of more than one male without conflict. This is the way of life for the endangered California desert tortoise. Male tortoises relentlessly pursue one another and attempt to turn their opponents upside down. There is little hope of them ever living compatibly together. The two male desert tortoises I have in my care at home live proximate but entirely isolated existences, despite all of the well-wishing sentiments that we have in caring for them. They hibernate for months in adjacent boxes in our bedroom closet, only inches apart, but live entirely apart the rest of the year when awake.

  Like people, animals get bored, which can lead to destructive and undesirable behaviors. The animals that exhibit this to the greatest degree are the primates. Most animals become bored because they are unemployed from the time that they arrive at the zoo. In the wild, most of their waking hours are spent in foraging, predator avoidance, and social engagement. In captivity, all the groceries are provided, usually in forms that require little investigation, preparation, or manipulation prior to consumption; zoo animals were eating fast-food meals long before most of their human counterparts were. Husbandry programs that make efforts to provide animals with occupational therapy are rewarded by the reduction in negative behaviors of boredom, and also create richer visitor experiences.

  Because of boredom, animals may carry out many undesirable activities, such as st
ereotyped locomotion, overgrooming, stool-eating, self-stimulation, exhibit destruction, regurgitating and reingestion, fecal flinging, and aggression. Our baboon groups at the zoo experienced noticeably reduced social tension and boredom when items such as uncooked rice and millet seeds were scattered through their exhibit several times daily. They spent large amounts of time finding and gathering up these bits of food. Animals that might ordinarily pick on others seemed to have an occupational release by walking around and methodically gathering up tiny food morsels, one grain at a time.

  Many zoos use puzzles or other devices that require animals to search for some of their foods and solve simple problems to acquire their daily rations. Chimpanzees have been conditioned to insert small sticks into artificial termite mounds to extract small sticky treats—often spaghetti sauce or oatmeal—similar to the termite-feeding behavior of chimps that has been documented in the wild. Some animals are challenged to discover concealed raisins, nuts, mealworms, and sundry nutritional tidbits, in the spirit of a daily Easter egg hunt. Animal groups are often fed multiple times daily in smaller allotments to reduce hoarding and improve the equitable distribution of foodstuffs.

  Because of the close confinement of animals, sanitation can be a significant problem. However, some of the traditions concerning cleaning zoo exhibits have been questioned. The most common cleaning practices involve lots of soap, water, and bleach to remove soil left by feces and food. It is not known how this hypercleansing affects animals’ natural behaviors related to scent-marking in their territory, or what social consequences result from this practice—a consideration for additional behavioral work in zoos.

  Husbandry research with primates has revealed some innovative alternatives to cleaning traditions. One such approach involved housing primates with a technique called “deep-litter bedding”—a composting technique. No group of zoo animals experiences more cases of diarrhea than zoo monkeys, and their care for such problems has always consumed much veterinary effort. The typical list of “rule-outs”—the likely causes of the problem that must be systematically eliminated—involve diet, parasites, infection, and stress. (In fact, it seems that several of these factors often interact to give rise to the problems.) The floors were covered deeply with wood chips or straw, and when they became soiled a fresh layer was added to the top. Layer by layer the floor litter was built up. Only periodically was the entire decomposing substrate replaced. The results of utilizing this compost-bedding technique were convincing from both behavioral and disease standpoints. Normal husbandry practices employed the frequent hosing away of wastes, which produces floors that are wet and contaminated, as well as frequent animal contact with aerosolized feces. With the deep-litter approach, animals spent more time on the ground foraging for their food, and the incidence of gastrointestinal disease diminished significantly; they also experienced fewer cases of aggression, injury, and abnormal behavior. As the bedding accumulated and aged, it actually inhibited the growth of bacteria as urine was absorbed and decomposed along with the feces.

  The constant addition of the litter substrate provided new opportunities to replicate normal feeding behaviors of monkeys by requiring greater exploratory efforts in acquiring food. In the wild, some primates are estimated to spend as much as 70 percent of their active times finding their food, during which significant social interaction takes place. For species that spend large periods of time ground in their natural environments, this sort of novel approach is the type of innovation that zoos need more of. The monkeys were no longer unemployed, but their keepers periodically had a big shoveling project to remove the accumulated litter, which is a laborious down side to the practice. The use of the deep-litter method has been limited by both practical concerns about the attractive nuisance that it provides for rodents and insects and aesthetic concerns for visitors. Judging by the state of my teenage son’s room, though, I am convinced that primates of all kinds take naturally to deep litter, and I continue to be intrigued by this approach.

  Health staff observing a gorilla at the San Diego Zoo

  8. WHAT’S THIS THING?

  Searching for the Normal

  Only thirty years ago, there were no textbooks, no classes, and few training programs in zoo animal medicine. Every practitioner had to start from scratch to learn what was even normal. At one time or another in their career, each zoo veterinarian has probed, prodded, biopsied, or at least puzzled over structures that turned out to be normal for that species. For example, the first time that you observe spider monkeys climbing around in a tree you can’t help but assume that the ones with the little dangling appendage on their rear ends (the size of a finger) are the males, although it turns out they are the females. The external genitalia of male spider monkeys, while respectable by monkey standards, is surprisingly more obvious than that of a four-hundred-pound gorilla, which can hardly be seen except when it is sedated.

  When I first examined a male koala as a zoo intern, I noticed that he had a discharge coming from a swelling in the middle of his chest, and I suspected a draining tumor or cyst. This was the only male koala in the world outside Australia at the time, and the chests of the only two females looked normal by comparison. Fortunately, my concern was delayed long enough to find out from a biology book that male koalas have a scent gland in that location, which they use to mark trees in their territories. Happily, I avoided a surgical blunder by leaving his alone.

  Zoo veterinarians routinely rely on changes in an animal’s typical individual behavior as indicators of illness. In many cases, observation, rather than leaping to hands-on diagnostics, may be the best method of understanding a problem. Elephants, for example, ordinarily lie down to sleep for a period of time each night, even though it may last for only three to four hours. Ill elephants, however, have been known to remain standing for months at a time. Like horses and cows, rhinos and other large herbivorous species, such as elephants, can doze for short periods of time while standing up, but all of the large herbivores in zoos, including the giraffe, should lie down to sleep at night. Failure to follow such a routine is a cause to suspect illness.

  Veterinarians are trained to recognize disease by classical clinical “signs.” A good example of this principle is the use of so-called textbook pictures. Imagine yourself as the author of a medical book or article, or giving a lecture to veterinary students. You want to illustrate a particular disease, but, as we all know, photographs seldom do reliable justice to the subject. Therefore, more extreme, obvious cases are chosen that have progressed to the stage where even the near-blind could not miss the visual presentation. These cases often come from situations of neglect, where the owner or attendant ignored the problem far past its initial signs and let it become a textbook case. Most veterinarians are not consistently presented with the classical images of a disease; rather, we often see diseases in their formative stages. If you observe embryos throughout their development, it is remarkable how similar a human, pig, dog, and cat are in the earlier stages. It is only after many important developmental steps that they each begin to gradually emerge as recognizable species. Such is the case with diseases—they share many general characteristics, such as fever, lack of appetite, lethargy, and discomfort. They all have to start at some point and progress to a recognizable stage. The first challenge is for owners or keepers to recognize that something is abnormal to decipher the emerging problem at the earliest point possible.

  Not all of the listed symptoms or signs described for a disease may be present. Textbooks enumerate the most common manifestations of a disease, but that seldom means that they all will express themselves in each case, even if left untreated. Not all animal hosts are created equal, each having their own unique characteristics, such as age, environment, genetic background, nutritional status, and immune competency. The effects of a disease are expressed through these backgrounds and ultimately determine their severity, significance, and clinical portrayal in an individual.

  In fact, technically speaking, animal
s do not have “symptoms” at all, since this term is defined as the “subjective” observations of a human patient (pain, numbness, confusion, depression), rather than objective (observable or measurable) conditions, which are referred to as “signs,” such as fever, skin rash, lameness, and swelling. Few things are more frustrating to the veterinary student or new practitioner than to be presented with sick animals whose signs of illness are vague and “incomplete.” Most of those signs don’t look like they do in the textbooks, but show more gradual and changing indications of disease. The overwhelming dilemma for a new clinician is that the list of possibilities of what can go wrong is huge, but lack of experience prevents one from tempering this list with the insights about what is likely to be going wrong in a particular case.

  Learning the normal anatomy of the animals in the zoo is a formidable undertaking and can never be adequately accomplished. Every animal that died in the San Diego Zoo was examined by a pathologist, creating many hands-on learning opportunities. Gradually, as zoo veterinarians have pursued their own favored groups of animals, they have integrated a broad knowledge of anatomy, pathology, and clinical disease. There are now veterinary subspecialties in avian, reptile, amphibian, marine mammal, wildlife, and primate medicine.

  In contrast to a zoo clinician, about the only fatal mistake that a zoo pathologist can make is doing a necropsy on a live animal, which has happened a few times in reptiles. Over the years, the San Diego Zoo reptile department brought several animals for postmortem examinations that were (it was later determined) still living. Declared dead by the keepers, they had been temporarily placed in holding coolers. Several snakes and tortoises, disconcertingly, later came back to life. One poisonous snake had been placed on the necropsy table by a pathologist to warm up for several hours prior to dissection, and it turned up missing when the pathologist returned to the necropsy room. He went around the hospital in search of the snake, suspecting a prank. When no one confessed, he returned to find the snake alive and coiled on the floor next to the leg of the necropsy table. It was returned alive to the exhibit collection. After that episode it was mandated that all poisonous snakes have their heads removed prior to necropsy. The clinical veterinarians, however, had no such luxuries of safety and always had to work on the poisonous snakes with their heads on. Perhaps this is another good reason to be a pathologist instead of a clinician.