We are what we eat in more ways than one. All animals use food to fuel their engines and ultimately build and rebuild body tissues, organs, and countless other spare parts. What an animal eats, therefore, winds up in each and every cell. Its diet also dictates how it will find its food and, ultimately, how it will live its life—whether it will be sedentary, roving, social, or solitary.
MEAT-EATERS Meat-eaters can find food in one of two ways. Predators kill other animals, called prey. Although you can’t see the actual chase and capture at the zoo, you can imagine which role an animal plays in the wild by studying its behavior and its body. The hunter and the hunted are locked in a biological cat-and-mouse game that’s been going on for millions of years. Each time the predator evolves a faster, surer, more clever way of finding and overcoming its prey, the prey evolves a countermeasure; just as the stalking lion’s movements become quieter, the zebra’s ears become more attuned to slight noises. This spiral dance of adaptations is a beautiful example of how natural selection constantly tinkers with its original designs.
Finding, subduing, or preparing prey to be eaten costs an animal both time and energy. Animals that specialize in prey many times smaller than themselves must contend with the problem of collecting enough to make a meal. Filter-feeders solve this problem by sucking in water that is clouded with small organisms and then straining out the good stuff. Baleen whales use their giant filtering mouth to trap shrimplike krill, and flamingos use their upside-down smile to dredge organisms from the mud. Insect-eaters, such as anteaters, shrews, and bats, are also handily equipped to gather enough of their tiny prey to satisfy their hunger.
Some meat-eaters, such as vultures, eagles, and hyenas, let other animals do the work. These scavengers eat the leftovers from other animals’ hunts or simply take advantage of animals that die of old age, injury, or illness. Their keen sense of smell allows them to ferret out decaying flesh no matter where it has fallen.
Although they don’t worry about getting attacked (corpses don’t fight back), scavengers do risk a certain amount of disease. To compensate, natural selection has provided them with a tolerance to foods that would make other animals sick.
Many scavengers, such as the bald eagle, can also hunt live prey if need be.
The way an animal gathers and eats its food in the wild can influence how it will be exhibited at the zoo. For instance, if an animal is used to defending a feeding territory, it may not take too well to having other animals in its enclosure. The urge to guard its food and the space around it is just too great.
Species that hunt alone, such as forest-dwelling leopards, are also more comfortable on their own or, at most, in pairs. Lions, on the other hand, crave company in captivity, perhaps because in the wild they depend on other lions to help them raise young and kill large, fleet-footed prey.
How specialized an animal is may also affect its comfort level in captivity.
For instance, some animals, such as eagles, snakes, and large cats, are extremely adept hunters. Their accuracy rate is so good and their prey is so filling that they need to spend only a fraction of their time hunting, allowing them to laze away the rest. In the zoo, these are the animals you’ll see sleeping or just gazing from a branch or hiding spot. This behavior is completely normal, true to what they would do in the wild.
Animals that don’t have a feeding specialty are called opportunistic feeders, and they have quite a different lifestyle in the wild. Instead of zeroing in on one type of food, they spend much of their time searching for anything edible, devouring it as fast as they find it. In sterile quarters, these opportunists tend to go stir-crazy because their natural tendency is to search and sniff, explore and check out their world. To keep these animals healthy, exhibit designers must build environments that continually challenge them.
EVOLUTION. Predators like this horseshoe bat are in a biological cat-and-mouse game with their prey. As bats hone their echolocation skills, moths develop better ways to escape. Some moths have evolved listening
membranes to detect bat calls, whereas others produce calls of their own that jam the bat’s sonar system.
PLANT-EATERS Even plant-eaters can be specialists, adapted for a particular feeding niche. You can recognize grazers, such as zebras, white rhinos, and buffaloes, because they spend most of their time with their head down, cropping grasses like giant lawn mowers. Since the grass they eat is not very nutritious, they must eat large quantities and pass it through their digestive tract quickly (look for lots of manure). This makes grazers the dryland counterparts of filter feeders; their digestive tract filters nutrients from the grasses, then flushes the remains through to make room for more.
Browsers look for hardier fare; they eat the twigs, buds, and leaves of woody plants. Koalas, sloths, and leaf-eating monkeys spend their lives in the branches, literally surrounded by food. Giraffes, elephants, and gerenuk antelopes use their
anatomical stepladders (necks, trunks, and long hind legs) to transport them to the canopy layer. Shrubs and trees in their zoo exhibits are usually pruned to the highest spot they can reach.
Fruit-eaters concentrate on the juicy seed containers that plants produce.
These are typically rich in water, carbohydrates, vitamin C, and sometimes oil.
The more animals that fruit-bearing plants can attract, the better their chances of having their seeds sprout next spring. The seeds eaten with the fruit travel through the animal’s digestive tract, often losing their hard shell so they are ready to germinate when deposited (conveniently) in a pile of fertilizing manure.
Flower-feeders have adapted ingenious ways to exploit the sweet, energy-rich nectar hidden deep in blossoms. As the long-billed hummingbird hovers at the mouth of a flower, its wings beat 50 to 80 times a second, up to a million times without pause. To fuel this stunt, the tiny birds must visit as many as 60 blossoms a day, consuming half their body weight in nectar. In a complementary adaptation, the flowers use the birds as a kind of pollinating service. They attract them with bright red petals and then bribe them with sugary nectar. Each hummingbird that dips its bill to drink brushes the flower with pollen from the last stop or picks up new pollen to bring to the next flower.
Seed-eaters, such as mice, chipmunks, and finches, have homed in on a truly nutritious and abundant source of food. Seeds are packed with fat, carbohydrates, and protein, and they usually keep well when stashed away in larders. As a result, seed-eating rodents and birds have prospered, becoming two of the world’s most numerous and widely distributed classes.
FOOD STORAGE Whenever there is a surplus of food, some zoo animals look as if they are playing with their dinner. A wolf that gets a bone for a treat, for instance, may eat some now, then bury the rest for later. Your own dog may try the same trick, digging fruitlessly into your living room carpet, trying to store the bone for a rainy day. In the wild, jackals, coyotes, foxes, bears, wolverines, mink, martens, and weasels have all been known to stash away what they can’t eat right now (a wild version of doggy bags).
Other animals hoard food by scattering it throughout their territory or piling it in one safe spot. Burrowing rodents cache their food in underground chambers so they can eat in peace, away from predators’ prying eyes. Animals that must
contend with winter, such as Arctic foxes, squirrels, pikas, beavers, and acorn woodpeckers, diligently stockpile food to get them through inclement times. To find out if a zoo animal is a food hoarder, watch for it tucking bits of food in the nooks and crannies of its enclosure.
FOOD HOARDERS. Acorn woodpeckers bore hundreds of small holes in a dead tree to store acorns for the winter.