However, not only did the results check out, they were an example of a phenomenon well known in humans. Psychologist Martin Seligman called learned taste aversion “Sauce Béarnaise Syndrome,” commemorating an occasion when he went to a restaurant, selected the steak with sauce béarnaise, and got dreadfully sick later that night. Despite learning that a strain of stomach flu that was sweeping his department had undoubtedly caused his illness, Seligman now found sauce béarnaise disgusting. It was 10 years before the visceral association between the sauce and the illness wore off. Most people can rant bitterly about some random food that they once ate before they got sick, and which they plan to avoid until the day they die.
Learned taste aversion is now well accepted and studied in creatures as simply laid-out as slugs. There is obvious survival value in not taking a long time to learn what foods make you sick. The price is that you learn some false associations along the way, but it’s worth it.
Despite the widespread occurrence of learned taste aversions, there are occasional exceptions. Researchers preparing golden lion tamarins for release tried to expose them to things they might meet in the wild. One day they put a large toad in the enclosure. The tamarins approached the toad cautiously and then like lightning two of them bit the toad squarely on its poisonous parotid glands. The shocked researchers snatched the toad, prizing it from the grip of a third, enthusiastic tamarin who also wished to bite the toad. Meanwhile the two that had gotten a taste began to foam at the mouth, vomit, and wail. One went into convulsions for hours. Their loved ones watched with interest. The next day, to test their assumption that the tamarins had learned a valuable Lesson About Toads, the researchers offered the toad again, in a glass jar. The tamarins were delighted to see a nice toad, and eager to get at it. For comparison, the researchers tried them with another glass jar full of their favorite grasshoppers. The tamarins, both those that had suffered toad poisoning and those that had merely witnessed toad poisoning, seemed exactly as wishful to get at the toad as the grasshoppers. The dismayed researchers suggested that maybe if the glass jar hadn’t prevented them from smelling the toad, the tamarins might have acted more appropriately. Nevertheless, noting that tamarins tried and sometimes caught and ate snakes, but that one of the released tamarins had probably died of snakebite, they wrote, “It appears that neither the affected nor the observing animals learned much from this near-fatal encounter. We must entertain the nonadaptionist hypothesis that captive and wild tamarins learn little about reptiles and amphibians: They try to eat the small ones, and if they are unlucky they may die.” Such examples of nonlearning show how valuable the ability to learn really is.
Learned taste aversion and uncertainty about what is good to eat can be exploited by humans, if they’re clever enough. Ingenious wildlife biologists in San Diego wanted to protect a colony of endangered least terns. These sporty little crested birds lay their eggs in open scrapes on flat coastal land. In other words, they nest just where you might want to lay your beach towel, and that’s one reason they’re endangered. This colony didn’t have that problem because they nested at a U.S. Marine Corps base, but they were losing a lot of eggs to ravens who nest in the coastal bluffs. Shooting ravens had not proved a successful strategy, since new ravens promptly moved in to the vacant raven territory and ate tern eggs.
The biologists took quail eggs, which look like tern eggs, made a little hole in each, and injected methiocarb, a chemical that makes birds feel extremely unwell. They sealed the hole with a bit of glue. The biologists then made fake tern nests on the bluffs near the ravens and put the nauseating eggs in them. The ravens promptly robbed the nests, but within a few days noticed that these eggs were ghastly, and stopped taking them. Learning to avoid nasty eggs at one site didn’t cause ravens to stop taking eggs from other places, however.
So the biologists tried setting up an elaborate fake tern colony, complete with protective fencing festooned with electrified wires and Keep Out signs. They made 20 fake nest scrapes and put bad eggs in half of them and untreated, perfectly good quail eggs in the other half. Ravens dropped in to eat eggs. The ravens quickly learned that some eggs were good and some were bad, and learned to tell them apart by handling them for about 25 seconds, abandoning the treated ones and eating the good ones. If ravens from elsewhere came by to check out the fake colony, the resident ravens chased them away.
The fact that the ravens could learn to tell good eggs from bad was discouraging. That meant you couldn’t just put bad eggs around the edges of a genuine colony with genuine tasty eggs in it.
But the following year, the biologists put out bad, treated eggs exclusively, planting them around the outskirts of genuine tern colonies—and they did this before the terns started laying eggs. The ravens speedily learned that all the eggs there were bad and stopped going there and taking eggs. By the time the terns began laying tasty tern eggs, the ravens had given up on foraging for eggs at the colonies. They still kept other ravens (who would not have learned about nauseating eggs) out of their territory. The result was that not a single tern egg was taken by ravens that year, and not a single raven was shot by predator control officers.
That wasn’t so bad
The opposite of learned taste aversion—learning to hate the taste of things that make you feel bad—is learning to like the taste of things that make you feel good. Alcohol owes our continued support to this form of learning. So, perhaps, does zoopharmacognosy, the practice by animals of treating their own ailments with medically active plants.
Chimpanzees seek out the leaves of certain plants and swallow them whole instead of chewing them. It’s hypothesized that in some cases they’re doing this to scour out intestinal parasites such as tapeworms and nodule worms. Whether this is learned behavior is unclear. No one has seen a mother chimp administering leaves to her infant. No one has to teach dogs and cats to eat grass blades, a behavior which is speculated to have a therapeutic effect on occasion. But animals have been seen to eat quite a variety of apparently medicinal plants—it’s hard to believe that they are such walking Merck Manuals that they have the innate ability to recognize them all.
But infant chimpanzees intently watch everything their mothers do. Two-year-olds put the same leaves in their mouths, chew, and spit them out. Not until seven years old are they seen to swallow them like adults.
In Venezuela, a troop of wedge-capped capuchin monkeys rub themselves with millipedes. Millipedes secrete powerful benzoquinones, which discourage predators from eating them. So powerful are the toxins that the monkeys who rub themselves with millipedes get enough on their fur to repel mosquitoes and parasitic bot flies, which can dangerously debilitate a monkey. The worse the bugs are, the more the capuchins anoint themselves. Sometimes the monkeys put the millipedes in their mouths for a moment to moisten them before they start rubbing, but they are never foolish enough to eat them. The benzoquinones are stronger than any mosquito repellents available for human use. One millipede may protect many capuchins, since one monkey passes it along to the next when the first one has completed the application of product. If they run out of millipede, monkeys rub against each other in an apparent attempt to get some protection.
Andy, a tame capuchin living with biologist Kathleen Gibson, is given an inch of cigar daily. Andy likes to rub himself with tobacco, orange rinds, onions, or garlic, as do many other capuchins. Gibson suspects that this self-anointing is good for Andy’s skin. “Andy is particularly prone to necrotic infections,” Gibson writes. “Since I began giving him tobacco on a prophylactic basis, he has had no skin infections.”
It’s not hard to imagine young animals learning to eat a plant that their elders often eat, and that makes them feel better, or to rub themselves with such a plant. How animals might learn to consume medicinal plants that are used only rarely is less clear. It is reported that zoologist Holly Dublin, observing elephants in Kenya, saw an elephant in an advanced state of pregnancy leave her normal range hurriedly, followed by her daughters. Sev
eral miles away she stopped at a tree and ate most of its foliage as her daughters watched. The elephant gave birth the next day. Dublin showed leaves from the tree to women in a nearby Masai village, and was told that they were sometimes used to induce labor. Did the elephant’s daughters understand what she was doing, and would they remember if they felt the same need? If so, that’s impressive.
Human medicine is full of examples of quack treatments and placebos. Most diseases go away, and if we happen to have taken a certain food or pill, or a certain treatment, right before we get better, we often believe that we were cured by the yogurt, or the ear-candling, or the magic spell to rid us of warts, when there was no connection. It seems possibly that animals would be just as likely to make this mistake as we are.
The junkyard bird
One culinary strategy is trying to eat everything you see. The keas of New Zealand have been dropping by the dump outside Arthur’s Pass National Park every day for 40 years to see what’s on the menu.
Things young keas have been seen taste-testing at the dump, according to biologists Judy Diamond and Alan Bond, include “rubber bands, string, masking tape, flashlight batteries, and foam rubber, among other unsuitable or dangerous materials. When trash was being burned, we even saw them attempt to bite the flames.”
This if-it-exists-try-to-eat-it behavior is appropriate for a scavenger. Bond and Diamond theorize that keas evolved in a harsh environment that was inhabited by moas (flightless birds that came in a range of sizes), who left nourishing carcasses when they died. When the Maoris arrived in New Zealand, they wiped out the moas, and perhaps this created even harsher times for keas. When Europeans arrived, their naturalists categorized keas as feeders on fruit and nectar, but maybe this was only because they could no longer find dead moas lying around. Europeans did not confine themselves to studying wildlife, and they introduced red deer and sheep. These died at the usual rate, but in the 1960s, because the deer had become wildly destructive, vast numbers were killed, and their carcasses dumped. Bond and Diamond speculate that this may have provided short-term bonanzas for keas.
Keas also scavenge dead sheep. They enjoy landing on living sheep and going for a ride. If the sheep has an open wound, they pick at it. This is bad for the sheep, who often die of infections in the wounds, and it has led to hair-raising stories of killer keas attacking sheep and eating them alive or carrying them off in their talons. (This is slightly more likely than me leaping out of this book and carrying you off in my talons.)
One can thus speculate that keas used to snack on moa carcasses in addition to plant foods, went through a difficult period where it was even harder than usual to find anything to eat, and then started snacking on deer carcasses, sheep carcasses, and garbage.
Favorite foods
Some animals learn a good thing to look for and make it a specialty. Sea otters in Monterey Bay, California, are under close observation by researchers, who have listed 33 types of prey the species eats. No otter eats them all. Marine mammal biologist Marianne Riedman lists the whims of otters she’s observed: Nosebuster ate almost nothing but turban snails, pounds and pounds of them. He’d swim into the kelp and wriggle violently, knocking snails loose “like ripe fruit shaken from a tree.” Female 508 liked the wily octopus, which she was very good at locating. The Ab Queen ate crabs and sea urchins, but mostly abalone. Another otter stole squid from the bait bucket kept on the stern of a boat in the harbor. One male caught and ate seabirds, whom he seized by the feet from underwater.
By watching otters over years, Riedman and colleagues were able to confirm that sea otters learn some food preferences from their mothers. (Obviously some sea otter has to invent stealing squid out of the bucket, once buckets appear on the scene.) Thus Female 184 ate kelp crabs, mussels, and turban snails, most of which she collected in shallow water, and her daughter Female 535 ate kelp crabs, mussels, and turban snails collected in shallow water. Both had an unusual feeding technique which researchers called the “surf grass salad bar”: they’d pull a clump of surf grass from the ocean floor, swim to the surface, and pick through the strands, finding and eating tiny crabs hiding there.
The refreshing beverage with tentacles
As early as the 1970s, at least one otter in Monterey Harbor had learned that soda and beer cans dotting the floor of the bay, tossed into the water by carefree litterbugs, often become starter homes for small octopuses. In a quarter of an hour, this otter was seen surfacing eight times, each time clutching a different can. Six had octopuses in them, and the otter bit open the side of the can, ate the octopus, and dived in search of another. Intrigued, researchers went down in scuba gear, looking for cans. They brought up 22 cans, 8 of which had already been ripped open, apparently by otter teeth. Of the remaining 14 cans, 7 had an octopus inside, and 2 contained onespot fringeheads, a fish which can be found lurking in tires, bottles, and shoes, if these things are lying at the bottom of a bay or slough.*
Maybe that’s what other tigers eat
Wild Siberian tigers are forced to compete with increasingly efficient human beings for their principal, but dwindling prey, elk. As a result some desperate tigers have developed unusual specialties. One tiger specialized in horses. Horses are big and fierce, and one horse kicked the tiger hard enough to break two teeth and a bone in its jaw. The tiger went right on hunting horses. Another Siberian tiger specialized in eating bears. It’s hard to believe that even a large tiger could get away with this for long.
A tigress in Malaya specialized in dogs, and killed and ate as many as three in one night. She ate them on the hill behind the police station, in a brushy spot littered with dog collars. She was shot by a dog-loving lieutenant colonel who enticed her using another dog as bait—after spending 10 days building a special cage for the bait dog that would keep it from being harmed by the tiger.
Becoming a specialist can be risky. Dingoes often consume a wide variety of prey, and the list of species they are known to hunt comes to 177, from magpie geese to wombats. But sometimes dingoes focus. On Australia’s Barkly Plateau, there are periodic population booms of the long-haired rat. In the early 1970s there was a long boom, and several generations of dingoes grew up feasting on long-haired rats. When the rat population crashed, many dingoes seem to have been unprepared to switch, and some starved to death in the midst of abundant prey such as pipits, songlarks, and other birds nesting on the ground. Growing up in the heyday of the long-haired rat may have produced young dingoes with an insufficiently broad education.
Dingoes who were accustomed to hunting kangaroos took a long time to learn that sheep are edible (something many people would prefer they never discover). Dingoes that grew up near sheep paddocks were skilled at hunting sheep and inept when they encountered kangaroos.
It is speculated that if dingo pups grow up hunting a wider variety of prey, they will be better able to learn to hunt new prey than dingoes that grew up as specialists. On the edge of the Simpson Desert, a population of dingoes hunted a variety of small vertebrates. When these became scarce, they switched to eating big flightless grasshoppers—and survived.
Where do you keep the food around here?
Once you know what’s good to eat, you have to find it, and food will sometimes hide from you. Extensive experiments, mostly with birds, have been done to clarify the concept of the search image, a mental picture of what a creature is searching for.
In classic experiments with stick caterpillars, which look deceptively like twigs instead of like fabulous little packets of nutrition, captive-reared European jays were put in aviaries containing stick caterpillars and actual sticks. These young jays had never seen stick caterpillars before, although they had been given a session with sticks so that they wouldn’t be alarmed by them. They were put in an aviary with the real and the fake sticks. Completely fooled, they had no idea there were caterpillars around. Eventually a jay would accidentally find a caterpillar, generally by stepping on it. (In the wild the caterpillar would be less apt to be
in a place where it would be stepped on, and it would probably be sticking out from another stick, exactly like a little dead branch, but the experimental caterpillars were dead and so could not employ these arts.) After this some jays would start grabbing every stick they could find. Others, now that they knew that a caterpillar could look like a stick, seemed to know at once how to tell mere plant matter from mimics, and would jump around the aviary snapping up caterpillars.
The Bornean orangutans, or “brilliant botanists,” studied by Biruté Galdikas and her colleagues eat more than 400 wild foods, which Galdikas summarizes as “a highly diversified mix of fruit, leaves, bark, sap, insects, shoots and stems, honey, and funguses.” They seem to learn that if one tree, say a durian, is bearing fruit, then other durian trees are also likely to be fruiting. Since trees in the rain forest are scattered, rather than growing in convenient groves, orangutans need to remember where they have seen other durians. They appear to have mental maps that allow them to travel directly to the places they remember.
Young California condors who grow up in the wild can follow their parents to food once they’ve fledged. Then they learn to scan for other scavengers and fly over to see what they’ve found. In their habitat, the first creatures to arrive at a carcass are likely to be turkey vultures, which have the advantage of a fine sense of smell. Ravens and golden eagles and sometimes even bald eagles are also promising indicators that food is available.
Janis Carter taught her chimpanzee charges how to rob nests. Having gotten them used to eating eggs, she sneaked out and tied old nests in absurdly obvious spots along the trail she would lead them along in the morning, and loaded the nests with eggs. From robbing these phony nests, they learned to watch for the sight of nests, and eventually became proficient egg-hunters.
Becoming a Tiger: The Education of an Animal Child Page 19