Life at the Zoo

by Phillip T. Robinson

  Some species are poorly represented in zoos because of failures in converting animals from wild to captive-diet substitutes. Concentration camp inmates of the World War II era sometimes succumbed to the well-intentioned efforts of their liberators, through the overwhelming stress caused by acute ingestion of nutritious foods. Similarly, providing unlimited amounts of certain foods to debilitated animals may overtax their ability to cope. Sudden dietary prosperity often causes indigestion, bloating, and death. Reversing serious malnutrition should be approached in a manner similar to that used to restore normal body temperatures in hypothermic patients—gradually.

  The North American moose has been notoriously difficult to keep healthy in captivity and, for perhaps both nutritional and behavioral reasons, moose have never adapted well in zoos. Those that survive are often sorry-looking specimens. Despite efforts to develop diets that duplicate the composition of natural moose foodstuffs, it seems that moose are not yet destined to become a common zoo exhibit animal. Some years ago, a motion picture director and his Canadian animal trainer telephoned me from their woodsy filming location in Oregon. Both were in a panic about the concluding scenes of their movie and had been working overtime to finish it. Among the crucial animal stars in the final scenes of this drama were two tame moose, “Bullwinkle” and “Rocky,” that had had diarrhea for the past five days. We discussed the history of these two creatures in detail—how well they were trained, the extremes that the trainers had gone through to condition them to riding in a truck, waiting calmly for a scene, tolerating lighting effects, and moving in and out of camera views as needed. After suffering through this lengthy history, we finally reached the current problem: persistent watery stools. Things had nearly come to a halt on the movie because neither moose could complete a scene without acting as though it was about to go relieve itself.

  Not suspecting some infectious plague of moose, and fresh out of intelligent medical questions, I finally asked, “How do you teach the moose to do all of these things anyways?” The Canadian trainer said, “Aye, they will do anything for bananas and that’s what we give the buggers.” I said, “You mean you have to give them bananas to do everything.” “Aye, just about, yes, we do,” he said. “But they never get tired of them no matter what because we’ve been filming for seven days in a row now and they still like ’em.” Cringing a little in anticipation of the answer, I asked, “And how many of these bananas do you suppose they have been eating every day for the past week?” “Oh,” he replied, “I guess that would be between aboot fifteen and twenty pounds each per day, but yesterday they had more—we worked late, you know. Aye, do you think that might be the problem?” For a few moments I was speechless.

  Many of the recipes for feeding animals that can keep them alive have been derived from uncontrolled experimentation, personal preference, food availability, and practical experience. The following is such a recipe for a baby elephant formula that we used in the San Diego Children’s Zoo. Like many zoo diets, its origin is a mystery, but the elephants did well on it. There are now, however, diets for baby elephants that are somewhat more scientifically formulated.

  Baby Elephant Diet

  1 cup cooked rice

  1 cup cooked barley

  3cans evaporated milk

  1 tablespoon of calcium tribasic

  4 tablespoons of honey (optional)

  Mix ingredients and add sufficient water to equal 1 gallon.

  Feed three times daily if animal is over 1 year of age and is eating other supplements. If younger, feed every 2–3 hours.

  Continuous shaking of the bottle while feeding is necessary to prevent rice and barley from settling to the bottom.

  Supplement this with Sudan hay and cut-up vegetables and fruits.

  Feeding animals in groups poses additional challenges to proper zoo nutrition, for individuals vary in their nutritional requirements by age, sex, and reproductive status. This often makes it necessary to feed all animals in a group at a level meeting the nutritional requirements of the most demanding individuals present, such as the young and lactating females. Group social issues also add complexity to mixed species and age exhibits. At the San Diego Zoo, we experienced a series of deaths in one of the large walk-through aviaries, which housed dozens of bird species in a forest-like setting. The principal findings on postmortem examination were “malnutrition” or “starvation,” but there was also evidence of trauma, as seen in bruises to the skin and underlying tissues. Several of the bird keepers took offense at these diagnostic labels because they consistently fed a substantial quantity and variety of quality foods and were far from neglectful. But the pathologists stuck to their guns. When activities in the large walk-through aviaries and at the feeding stations were observed closely, everyone, including the keepers, finally agreed that the problem lay with some birds aggressively defending their feeding sites. They simply prevented more passive species from eating and harassed those that tried. “Starvation” was probably an apt description after all. As soon as the numbers of feeder stations were increased and placed at different heights and locations, the mortalities dropped dramatically. The total amount of food fed was aboutthe same.

  In the wild, herbivorous animals spend large amounts of time foraging for plant foods, and it is desirable to parallel this behavior in captivity. However, few zoos are able to provide naturalistic exhibits with the variety of living food choices found in the wild. When cafeteria offerings of domesticated food items are provided, some individuals will monopolize favored feedstuffs, such as grains and protein supplements, at the expense of other animals in the exhibit. To overcome this problem, many zoos began feeding nutritionally complete pelleted diets along with hays, making it more difficult for dominant animals to overindulge on preferred feeds. As with the birds, multiple feeder stations also help to provide more equitable distribution of food. Nourishment of young, socially subordinate herbivores may be accomplished with “creep” feeders, which are designed to allow smaller animals physical access to more nutrient-dense food while excluding adults with less demanding nutritional needs.

  Even animals with comparatively simple dietary habits, such as wild carnivores, have had their share of nutritional problems in captivity. Failing to take into account the nutritional contribution of all parts of a whole animal that would normally be consumed by a predator, many zoos have attempted to raise and maintain carnivores exclusively on muscle and fat. Meat alone has a low calcium concentration and an imbalance of the minerals calcium and phosphorus, which is ordinarily compensated for by consuming the non-muscle parts of prey. I once received a radiotelephone call from a South American ranch, where the owner’s family was hand-raising several ocelots, small spotted felines from the region’s forests. After bottle feeding and weaning, the cats had grown rapidly into beautiful little creatures with glossy hair coats. But they were becoming lame and having difficulty walking, all due to their unbalanced, all-meat diet. The owners readily accepted recommendations for adding calcium to the diet, and the ocelots made rapid progress in subsequent weeks and became quite normal.

  In similar nutritional scenarios, dietary imbalances have been commonly identified in meat-eating birds, reptiles, and amphibians. The zoo carnivores that have experienced fewest problems are the ones consuming whole prey, such as hawks, owls, crocodiles, lizards, seals, and sea lions. This assumes, however, that if these carnivores are fed colony-reared rodent and avian prey or farm-raised fish, the diets of the prey species must be optimized with respect to their content of essential vitamins and minerals.

  Other parallel pitfalls have been noted in reptiles and amphibians fed diets of crickets, mealworms, or wax moth larvae, which tend to be low in calcium as compared to phosphorus. The techniques of nutritionally adjusting the composition of these insect creatures to make them more suitable as a balanced food are now well known. They were dusted with supplement powders in the past, but these supplements are commonly lost as the insects move or groom themselves. Much m
ore successful is the provision of a customized insect food that leaves a high-calcium, nutrient-rich residue in the insect’s gastrointestinal tract. So when they are consumed by an insectivorous predator, the insect plus its gut contents comprise a nutritionally balanced meal. Calcium metabolism is also dependent upon the presence of vitamin D in the diet, or access to the sun or an appropriate artificial source of ultraviolet B (UVB) irradiation. Historical efforts to keep these animals healthy in captive environments were often compromised by a lack of understanding of these crucial factors.

  Apes and most monkeys have nutritional requirements generally similar to those of humans, including mandatory requirements for vitamins C and D. Deficiency of the first will cause scurvy, and, of the second, rickets or osteomalacia. In climates where ample natural sunlight is available, captive primates can produce their own vitamin D from metabolic precursors. Many of the cases of rickets in zoo primates are in multiseason, temperate climates where indoor housing and the absence of proper amounts of direct sunlight are limiting factors. Window glass filters out the wavelengths of light that are required for vitamin D synthesis, and young animals with rapidly developing skeletons are more vulnerable to deficiencies than adults. For many years the cause of bone deformations in captive monkeys was not understood. Some interpreted the problem as being caused by confinement in small cages and called it “cage paralysis.” The typical findings included bowed and thickened bones and collapsing vertebrae. Animals became crippled and immobile and were unable, or reluctant, to move about, even to obtain food that was placed in their cage. These invalids would often lie around their cage bottoms, losing use of their arms and legs, and their muscles wasted away for lack of use. Finally, in the 1930s, two vitamin D forms were isolated and their structures determined, and the role of this nutrient and sunlight in cases of cage paralysis eventually became known and incorporated into primate husbandry routines.

  Two forms of vitamin D are found in foods: vitamin D2 in plant and fungal tissues and vitamin D3 in animal tissues. Although vitamin D3 is most biologically active in the monkey species that have been studied, Old World macaques seem to use either vitamin D2 or vitamin D3 quite well, whereas New World capuchin monkeys, spider monkeys, howler monkeys, and tamarins seem to be significantly more responsive to vitamin D3. Contemporary commercial primate diets now scrupulously include the D3 form of this vitamin (and vitamin C), but baby monkeys kept indoors and that depend on their mother’s milk (and little other food) for an extended period can still fall victim to rickets.

  Zoo primates can be resourceful in supplementing their diets with the local bird fauna, and I observed this on a number of occasions in the San Diego Zoo. One small group of gibbons, long-armed and highly arboreal monkeys, lived on a small island exhibit and waited patiently on their elevated bamboo perches for birds. It was impressive to observe a gibbon stab its arm overhead into the air, snatch a surprised bird in mid-flight, and eat it. A male Barbary macaque monkey in the zoo was much more premeditated about his quest for sparrows and grackles around the monkey yard. Birds played an important role in his daily life. He was most successful when the public was in the zoo and birds were lulled into a false sense of security. Sitting by the wire front of his cage, he would place several small, carefully spaced morsels of monkey biscuits within his reach on the ground outside. Calculating and patient, he waited with his feet propped on the cage wire and his arm strategically placed within striking distance. Nonchalantly, he anticipated the arrival of his prey. As small birds hopped innocently toward his bait between him and the visitors, he grabbed them with lightning speed. To the shock of the visitors, he stuffed them into his mouth, and then fastidiously plucked out the larger tail feathers and discarded them on the floor. One horrified child, who I observed witnessing this microcarnage, recoiled from the sight and exclaimed, “Ooh, gross, mom!” In contrast, San Diego’s first two gorillas, Mbongo and Ngagi, acquired as youngsters in the 1930s, were reported by Belle Benchley in her book My Life in a Man-Made Jungle to be observed gently holding a live chicken that made a habit of straying into their cage, making no attempts to harm or devour the bird. On the other hand, a keeper observed them playing with a feral rat by picking it up and dangling it by its tail. When the rat finally bit one of them, they tired of the game. The dangling rodent was dropped into their water pool, where they closely observed it until its demise. It alternately swam and sank until it finally came up no more. Mbongo then retrieved the body from the water and laid it out on a shelf near the keeper.

  Animals sometimes survive in captivity even if they do not eat the food we offer them. The keepers at the zoo hospital were concerned because a small African carnivore, an aardwolf, had not eaten since her arrival. We weighed the animal to compare with her arrival weight, and to everyone’s surprise she had actually gained a few ounces. One night when I came in to the hospital to tend to a sick animal, I walked quietly through the back animal ward, and in the subdued light I witnessed our little aardwolf chasing cockroaches and swallowing them like bits of popcorn.

  The red and pink feather pigmentation of some birds, such as flamingos and roseate spoonbills, results from regular ingestion of natural carotenoid pigments that are present in their wild diets of crustaceans, insects, and algae. Early captive diets for flamingos often produced disappointing losses of plumage coloration. This problem can now be solved by providing diets containing somewhat costly synthetic or natural pigment products, such as the pigment roxanthin, found in red or dried powdered shrimp shells and carrot oils.

  In addition to the inadvertent omission of important nutrients in zoo animal diets, the manner in which foods are processed and stored may also lead to malnutrition. Some of the fish species commonly fed to marine birds and mammals may be altered in nutritionally significant ways when they are frozen and stored—a common historical practice. Thawing frozen fish with running water results in loss of some water-soluble nutrients. Thawing in a refrigerator avoids this problem and inhibits microbial growth that might occur when thawing at room temperature. Of course, this approach, because it is slower, requires advance planning to ensure that thawed fish are available when needed. Another common fish storage problem has important implications for the supply of the B vitamin, thiamin, a dietary nutrient essential for health. Thiamin is present in generous supply in whole prey, such as fish, and is obtained through normal digestion and absorption. Freezing, storing and thawing fish, especially herring, smelt, and mackerel, may allow the enzyme thiaminase in fish liver to destroy thiamin, causing a deficiency in fish-eating zoo animals, such as seals, sea lions, and sea birds. Thiamin shortage can lead to neuromuscular weakness and cardiac problems. This can be avoided by placing thiamin tablets in the gills or mouths of fish or injecting them with thiamin solutions before feeding them.

  Kenton “K.C.” Lint, an elder statesman of bird curating at the San Diego Zoo, was a great lover of bird feeding recipes and anecdotal husbandry advice. In recounting some of the idiosyncrasies of living a lifetime with a bird nut, his wife, Marie, once complained to me about all of the strange things that she regularly found in his pockets before laundering his shirts and pants. These ranged from sunflower seeds to wriggling mealworms, crumbled crickets, and live anolis lizards. K.C.’s habit was to feed his favorite specimens as he toured his bird collection in the zoo. Years before, he had impressed his zoo curator peers by repeatedly breeding some rare macaw parrots for the first time. The “secrets” that were touted as the defining factors of his success were the nesting box that he provided in which these parrots reared their young—a used wooden whiskey barrel—and a diet that included fresh corn on the cob. For years, many zoos with this parrot species tried to emulate his accomplishment; whiskey barrels became common zoo parrot domiciles around the world. Keepers and curators from other zoos and private collections used to contact the zoo to be sure they were getting the correct barrel size and were using the same diameter opening through which the birds could enter. Some even wanted to
know the brand of whiskey and the time elapsed since the barrel had contained liquor. Despite this passion for detail, nearly everyone else failed to replicate this breeding success, while these original birds continued to produce babies in their whiskey keg.

  Such is the nature of popular recipes for success, whether they are birdhouses or diets. Transport those same successful birds and their whiskey barrel and corncobs to another zoo, however, and they might stop breeding altogether. However diligent our search for optimal ways of feeding animals, some in the zoo profession will undoubtedly continue to use a blend of folklore, witchcraft, and science, and there will be strongly held preferences, just as there are with the feeding of our most common household animals, our domestic dogs and cats. I can only hope, with our developing knowledge in comparative nutrition, that the rational application of science to the feeding of zoo animals will prevail.

  While the longevity of zoo animals has steadily improved with better housing, management, disease control, and nutrition, the current nutritional trend is toward obesity in Americans. Contrary to the zoo experience, some experts are predicting that today’s human children may be the first generation to have a life expectancy shorter than their parents.

  Chimp with pneumonia at the New York Zoological Park, c. 1905

  12. GETTING CLOSER TO ANIMALS

  Judas Goats and Alpaca Coats

  Leave it to veterinarians to try to help animals only to have their good deeds backfire. Our single alpaca in the zoo had accumulated an enormous thick hair coat. These South American hoofed relatives of the llama are adapted to cold climates in the Andes Mountains at altitudes of fifteen thousand feet, where they have been domesticated for hundreds of years for fiber and food. When summer came, I started worrying about our heavily frocked alpaca, who I was sure would suffer under the hot San Diego sun. Alpaca wool, which is as soft as mohair, is often called the “fiber of the gods” and is one of the most luxurious in the world. Its superior insulating and working properties make it prized by wool fanciers. During the annual visit of our sheep shaver to shear the Children’s Zoo sheep for the summer, we offered him the rare opportunity to groom an alpaca—something he could proudly talk to his children about, or at least within the social circles frequented by sheepshearers. He jumped at the chance.