Predation skills
For many young animals, the question of how you get your paws on the food once you spot it is a serious matter. The issue is particularly acute for species that need to catch living prey. Yet even picking food up is difficult for some babies. According to Marc Hauser, the young yellow-eyed junco (a dapper species of sparrow) is “perhaps one of the most inept foragers” among birds. It can scarcely pick up a mealworm without dropping it. Eating it is harder still. Adults are sometimes seen to hop over to a juvenile and rearrange the worm in its beak, so that it’s in a position in which the young bird can actually swallow it.
Wait, won’t you stay for dinner?
The difficulty of picking up food that lies still is nothing compared to the difficulty of getting your beak or paws on food that runs, swims, or flies away. While teenaged great blue herons foraging in the Gaspereau River in Nova Scotia paced along the shore or through the shallows at the same rate as adults and struck at prey items just as often, they caught prey on only 33 percent of their strikes, as compared with 62 percent for the adults. (You can tell when a heron catches something, because swallowing is so visible on their long skinny necks.)
The researchers criticized the striking technique of the juvenile herons, writing that they lacked adult “finesse.” Sometimes a wildly lunging young heron would submerge its entire head, which adults never did. The young herons practiced on floating objects like sticks or clumps of algae, repeatedly striking, seizing, and then dropping the object. “Pow! Watch this! Pow!” Grown-up herons never did this.
Young herons got better fast, however. When the scientists observed 10-week-old birds, they got something to eat on only 18 percent of their strikes. A week later, in similar weather conditions, 11-week-old herons caught prey 55 percent of the time, not far behind the rate of adults.
Adult Sandwich terns fishing on the coast of Sierra Leone were more competent than teenaged terns. Zoologist Euan Dunn noted that young terns sometimes caught a fish and then dropped it, but the adults never dropped one. Young terns caught fish on fewer of their dives. Adults caught 14 fish an hour, and the kids could only manage 10 an hour. They did about as well as adults when fish were close to the surface, but less well when the fish were deeper. The deeper the fish, the harder it may be for terns to judge where it is and exactly where to dive to nab it.
After weaning, eight orphaned red bats were placed in an outdoor aviary equipped with lights to attract insects. Once they had worked on their flying skills, the little bats noticed the moths and midges and would fly into a swarm and out the other side without chasing any one moth. In the mornings their bellies would be concave until rehabilitator Barbara French gave them their morning feedings. As the days passed, the bats began darting and jinking after their prey, and within a few weeks they had bulging bellies in the mornings. One bat was self-sufficient in a week, but three of them took six weeks.
Crumbs are for babies
Dippers are elegant little passerine birds who live by streams and make most of their living wading in streams eating insects and occasionally small fish. Often dippers dive beneath the surface of the water and forage on the bottom of the stream, keeping themselves in place with their wings in what may be a significant torrent. It’s hard, skilled work. Sonja Yoerg, observing young dippers in Wales, found that there is a juvenile strategy for gathering food, which involves picking a lot of tiny blackfly larvae—or “crumbs”—off rocks in shallow water. Crumbs don’t try to get away, which is handy for young birds, who are clumsy. Yoerg frequently saw them pick up larger food items ineptly and drop them or be unable to keep them from struggling free.
Sometimes a juvenile’s foraging netted a caddis fly larva. Caddis larvae, to protect their succulent bodies, build themselves craftsman-like tubular cases out of materials they find in the streambed, such as tiny pebbles, twigs, or pine needles. An adult dipper shucks the case off and eats the larva within, but Yoerg saw many instances of juveniles eating larvae, cases and all. “Consumption of caddis with its case may be a consequence of poor handling skills,” Yoerg writes.
Juveniles also caught fish at a low rate and were as likely to drop them as to swallow them. One 19-day-old bird caught a fish by the tail and took it over to its mother, who was foraging nearby. Gripping the thrashing fish in its bill, the juvenile made begging motions. Its mother grabbed the fish and ate it herself.
The trade-off between subsisting on parental bounty and doing the work oneself has been investigated in other species, and a major factor is just how long parents will cooperate. N. B. Davies looked at the transition from begging to independent feeding in wild spotted flycatcher fledglings in an Oxford garden. At first the little birds perched on a branch and called “Tsi,” which seems to mean “Feed me!” And at first the parents brought large tasty insects until the tsiing stopped. In this sated condition, the young birds looked around, pecked at things, and explored. Then it was back to Tsi! Tsi! With passing days the young fly-catchers began chasing their parents with their demands, instead of calling for their parents to come to them. They began grabbing insects away from their parents and banging the bugs against a branch. (This kills a bug, so it doesn’t wiggle going down, and perhaps makes it more flexible.) If they couldn’t swallow it after this, the adult bird would take the insect, bash it more thoroughly, and return it to the young bird.
It became harder and harder for the young birds to wheedle food out of their parents as they grew older, but at the same time they were getting better at feeding themselves. At first the young birds tried “stand catching,” in which you stand on a branch and wait for an insect to fly by in easy grabbing distance. Such insects are sadly infrequent, and by their third week young birds have more or less given this up. As they became better at flying, they attempted the skill for which they are named, fly catching, in which you spot a flying insect, fly over, and snatch it out of the air. It took the young birds about 8 to 10 days from fledging to reach a skill level at which they could catch three-quarters of the insects they went after.
As the parents became less generous to their demanding children, the young birds continued to beg for a while. They begged not only from their parents but from each other, “and sometimes briefly begged with quivering wings toward a fly as it passed them, before they flew out and caught it.”
These are birds that are independent of their parents in a few weeks. It’s not such a quick process for the hardworking white-winged chough.* These Australian birds laboriously sift through eucalyptus leaf litter, seeking the elusive arthropod. They live in cooperative breeding groups of 10 to 20, and all pitch in to build the nest, sit on the eggs, and raise the babies. The more choughs in a group, the better chance of survival the young ones have—a pair won’t succeed in keeping their young alive without help. When they have young, group members spend “virtually all” their waking time foraging for the chicks and themselves, whereas out of the breeding season, they need spend only 80 percent of their time toiling. The babies take more than six months to achieve independence. They continue to improve their skills over a four-year adolescence. But for the first 40 days they get almost everything through incessant begging. They can’t fly well yet, and so they walk along behind the foraging group, screaming for food.
Good caterpillars, bad caterpillars, and complicated caterpillars
Among the primates, squirrel monkeys, who mature quickly, need to learn foraging skills in a hurry. Once baby squirrel monkeys become mobile, they don’t stick closely to adults, minimizing their chances to observe or imitate. Researchers observing wild squirrel monkeys in a Costa Rican national park noted that most things squirrel monkeys eat are small, and that adults, even mothers, do not share these dinky food items with babies.
When they were just a month old, baby monkeys stuck everything in their mouths—twigs, leaves, pieces of bark. But soon they became focused on things they could actually eat. Before they were two months old, baby monkeys were seen tearing apart curled leaves
to find and eat caterpillars, and pulling leaves through their teeth to scrape off bugs.
The baby monkeys didn’t initially have great motor skills—they were seen fumbling katydids, dropping cicadas, missing grasshoppers, and letting frogs kick free. They had to learn techniques as well as simply acquiring strength and physical fluency.
One of the more complex skills squirrel monkeys learn is that of handling caterpillars with irritating or stinging spines. When grown squirrel monkeys pick up nasty caterpillars, they hold the tufty tip of their long furry tail in their hand so that it protects their hand like an oven mitt. Then, still using their tail tuft, they rub the spines off the caterpillar before eating. Researchers Boinski and Fragaszy describe seeing a baby monkey (106 days old) eating caterpillars without using the tail technique, and then spending several minutes rubbing its hands, as if trying to wipe away the sting. The next day they saw the same little monkey eating caterpillars, this time rubbing each one with its tail first.
The one example seen of adults helping baby squirrel monkeys learn foraging skills took the form of warnings about poisonous (not merely spiny) caterpillars. One June day, for example, the troop was crossing a forest gap along a branch. An enormous black caterpillar, apparently not as delightful to eat as it looked, was lying temptingly in view on a leaf next to the branch. Adults paused to look at the caterpillar and passed on, but when four babies stopped to examine it, an adult male came back, barked a warning, and stood between the babies and the caterpillar. They gave the creature a careful stare and moved on. Adults also barked and steered babies away from opossums, snakes, and owls.
Polar bear cubs stay with their mothers for two years, and their hunting prowess gradually improves. Ian Stirling, watching wild bears in the Arctic, found that one-year-olds spent only 4 percent of their time hunting. Two-year-olds hunted 7 percent of the time. Meanwhile, the average mother, hunting for the whole family, spent 35 to 50 percent of her time hunting. A mother might catch a seal every 4 or 5 days, but a yearling would catch one only every 22 days. The next year they might catch one every 5 or 6 days. But a one-year-old follows its mother closely, watching her, and sniffing everything she touches. When she starts to stalk prey, the cub lies down to watch and wait. Occasionally Stirling saw one get impatient and approach its mother too soon, whereupon she’d usually make a threatening charge at the cub or belt it with a forepaw. Then the cub would lie down again and wait as long as necessary.
Young dolphins observe and work to master parental technique. Dolphins at Monkey Mia in Australia round up schools of fish into a compact space and whack them with their tails, stunning a bunch of fish at once. This is apparently not something you or I could do on the first try, even if we had tails. Biologist Rachel Smolker writes, “It is not easy to smack a fast-moving fish. Once we knew what to look for, on many occasions in the shallows of Monkey Mia, we saw youngsters practicing, swiping their flukes at tiny fish, which they usually missed.”
There’s a special trick to eating these
When foraging techniques are observed in only one or a few areas, that may support the idea that they are learned skills (although environmental factors must first be ruled out—dolphins that live in the deep sea don’t have the option of chasing fish up onto mud banks, even if they think about it all the time). Hans Fricke has observed coral reef fish, including triggerfish, for decades. At one place, Fricke found five triggerfish who each used an unusual technique for eating sea urchins: they’d bite off the spines, which allowed them to grab it and carry it to the surface, where they’d let go and take bites from the unprotected underside as the urchin slowly tumbled to the bottom. Other triggerfish eat urchins, but do so by blowing water on them in an attempt to tip them over to get to the underside. The five triggerfish with the unusual technique are thought to have learned it from each other. (Presumably one particularly ingenious triggerfish, whom I refuse to call a “triggerfish Einstein,” developed the technique first.)
How to kill a gemsbok and live
Lions in the Kalahari Desert are said to use a special technique on gemsbok, antelopes with genuinely dangerous horns. F. C. Eloff reports that a gemsbok was seen going about its business with a decomposed leopard on its back: apparently the leopard pounced on the gemsbok’s back and the gemsbok stabbed the leopard to death with its horns. Then, faced with the dilemma of what to do when you have a dead leopard impaled on your horns, it had no answer. Eloff also reports a hyena stabbed to death by a gemsbok, a gemsbok found with its horns stuck in a dead lion, and two gemsboks found dead with dead lions they had stabbed.
Kalahari lions still file gemsboks under Large and Tasty, but instead of biting them on the throat, they often leap onto their hindquarters and break their backs, thus staying farther from the horns. Wardens in Etosha National Park told Eloff that the lions there never broke the backs of prey, suggesting that this is a regional variation. In Etosha there are more prey species, so it may be that the Kalahari lions, who have few other options than gemsbok, have had to come up with a technique.
Eloff observed small lion prides in the Kalahari, and the pride he named S2, which consisted of a pair of young lions whose skills were not yet honed, “provided us with a lot of amusement.” Extracts from the log show the bumbling duo chasing a gemsbok calf but not catching it. (Can you blame them?) Later that night they chased an aardvark. It went into its hole and they tried to dig it out. This did not work. The next day they chased a bat-eared fox into its hole and tried to dig it out. No luck. Two days later they spotted and chased an aardvark and, what do you know, it went into its hole and they were unable to dig it out. In the next two days they went after another bat-eared fox (no), a pangolin (no), and a porcupine (no). It’s the kind of record that forces a lion to take another look at the Gemsbok Diet.
In South Africa, entrepreneur John Varty and cat handler Dave Salmoni introduced two seven-month-old tiger cubs, Ron and Julie, to the task of hunting prey in a fenced preserve.* As shown in a Discovery Channel Quest show, Ron and Julie, although large and impressive, would never have survived without human protection. Initially, all they could think of to do with prey animals was to chase them, which is admittedly fun. When they found a dead zebra, they were thrilled and leapt on it and bit it in all the right places, but never thought of eating it.
By hanging dead antelopes from the back of a truck and driving away, Varty and Salmoni got the cubs to leap on the antelope and try to bring it down. That meant that they were teaching the tigers to chase trucks with mayhem in mind, so they switched to suspending antelopes from wires between trees.
The first prey the tigers caught was a porcupine, and if Dave hadn’t pulled the quills out of Ron’s face, chest, and paw, they might have worked their way in to create potentially deadly infected wounds.
They fearlessly approached Cape buffalo, who ran them off. Ron fearlessly chased a rhino, who fortunately decided to run, perhaps because he’d never seen such a creature before. Ron fearlessly attacked a herd of domestic cattle, and a cow gave him a serious kicking. But when Varty introduced a flock of tasty ostrich into their 150-acre hunting enclosure, Ron and Julie were terrified and hid for a week. Ron and Julie were given a dead ostrich to chew on, which caused them to realize that ostriches can be eaten. Shortly thereafter they killed one for themselves.
They could be seen becoming better hunters. The first warthog they chased vanished down a burrow, and they groaned in frustration. The next time they chased a warthog, Ron cut off its retreat and beat it to the burrow. The preserve provided so little cover in the form of trees and bushes that the humans had to show the tigers how to sneak along a sunken riverbed to ambush prey. The first time they killed a blesbok, Julie cleverly cut it off in a thicket, but her suffocating bite was ineptly administered. But after three years, the tigers were deemed “stalking machines”—fit to hunt for themselves.
With catlike tread upon our prey we steal
Cats have a great deal of innate technique to draw upon w
hen hunting for their prey, as anyone knows who has seen a kitten sneak up on an unsuspecting sock, pounce on it, seize it with jaws and fearsomely clawed forefeet, and disembowel it with mighty strokes of the hind feet. Yet despite the masterful way an inexperienced kitten handles hosiery, cats and great cats do have things to learn about hunting.
Tigers, lions, leopards, and cheetahs raised by humans and then reintroduced into the wild are pretty good at adapting to the habitat, whether it be jungle, forest, or savannah, and have little problem meeting, recognizing, and mating with other cats; and the females make fine mothers. But learning to catch and kill enough prey to keep alive (and to support cubs, if any) is more difficult. They practice pouncing on their playmates, but they seem to need to learn that they can also pounce on strangers. Then they need to learn to kill edible strangers, which can be quite difficult. They need to distinguish edible strangers who can fight back and should be left alone from edible strangers who can safely be attacked. They need to refine their lying-in-wait and stalking techniques if they are to find enough prey. They also need to learn how to eat a dead animal, as “opening” a carcass turns out to be surprisingly difficult.
Mother cats of many species do not teach kittens or cubs what to do, but diligently provide perfect learning situations. Often a mother cat starts by bringing prey, safely dead, and the kittens learn what their food looks like. Then some mother cats bring prey that is living, but injured, and the kittens witness how it is killed and try to kill it themselves. Then she brings them living, uninjured prey, and they learn to chase and catch it themselves. Thus, in a preserve in northern India, the tigress Noon caught a chital fawn and gave it to her cubs, who were not quite two years old. Overjoyed, they played with it as thoughtlessly as a kitten plays with a ball of paper, but couldn’t resist killing it before very long.
Becoming a Tiger: The Education of an Animal Child Page 20