An 18-month-old calf took a branch, snapped off a side branch, and switched flies with it. A 9-month-old calf tried but seemed too uncoordinated to actually succeed in switching flies. The researchers consider these cases of imitation and emulation, and hint strongly that elephants are just as good as primates any day.
Why not just whack it with a tire iron?
In 1974 a paper appeared in the ornithological journal Western Birds titled, “Do Crows Use Automobiles as Nutcrackers?” In 1978 a paper appeared in the ornithological journal The Auk titled, “Crows Use Automobiles as Nutcrackers.” In 1997 a paper appeared in The Auk titled, “Crows Do Not Use Automobiles as Nutcrackers: Putting an Anecdote to the Test.”
The first two papers each described a crow dropping a nut onto a road where it was run over by a car. The crow then hopped over and ate the meat of the nut. The first was a crow in Davis, California, which dropped walnuts on the road, and the second was a crow in Long Beach, California, which dropped a palm fruit on the road.* The third, 1997, paper described extensive observations of crows in Davis, on two roads lined with walnut trees. The authors concluded that the crows were dropping walnuts to crack them on the hard road surface. Cars might sometimes run over the walnuts, but the crows were no more likely to bring walnuts to the road or to drop walnuts on the road when a car was coming than when there were no cars in sight. Moreover, 200 cars passed without running over a walnut. While the researchers could not rule out the possibility that crows ever harnessed the automobile in their culinary endeavors, they wrote that “their putative exploitation of moving cars is not adequately documented and should not be cited as an example of avian intelligence or adaptability.”
More recent reports say that carrion crows in Sendai, in northern Japan, have been seen cracking walnuts under the wheels of cars. They don’t drop the nuts, but place a nut on the road and then hop back until a car runs over it. This is said to be advantageous to younger crows. The idea put forward by researcher Yasuhiro Adachi is that for an adult crow it’s just as easy and more reliable to simply drop the nut, but that inexperienced young crows tend to waste energy by flying too high when they drop nuts.* They save energy by using the car method.
Crows won’t use this method unless they know how, and also have access to a suitable area with plenty of cars, a red light to make the cars stop from time to time, and plenty of nuts nearby. And adult crows have no reason to bother, so it’s logical that the technique isn’t more widespread.
Strange doings in New Caledonia
Crows and their relatives are frequently cited as nonhuman tool wielders. Heroes of this kind are the crows of New Caledonia, who display their prowess in the laboratory and in the wild, even when being filmed by the BBC. They use tools, they make tools, they make standardized tools, and they take their tools with them from place to place. One wild crow was seen arriving at a foraging site in the morning with a tool in its bill. It only remains to find that they hang their tools on walls with painted outlines of the tools to show where each one should go.
They make hooked-twig tools, from which they strip the bark and leaves, and use the hooked end to fish in holes and crevices for insects. They also make stepped-cut tools, which they cut from the edges of pandanus leaves. These are long and pointed and have small barbs on one side.
When foraging for the larvae of longhorn beetles in dead wood, crows make tools out of dry leaf stems, or out of twigs which they find on the ground or snap off nearby trees. The basic concept is that you annoy the larva by poking it, it unwisely grabs the tool in its jaws, and you pull it out and eat it. Sometimes it takes as much as ten minutes to dupe the larva into doing this.
A juvenile crow with this foraging party begged, and was given pieces of larvae by adults. The young crow looked into holes that adults were probing. (Usually this was tolerated, although once an adult shoved the kid away.) Sometimes the young bird picked up a tool that an adult had put down, and probed in the hole where the adult had been working. Twice, young birds tried incompetently to make tools, once using a piece of grass (too flimsy) and once holding the wrong part of a leaf stem it was snipping the leaf from, so the stem fell on the ground. “Adults did not behave like this, suggesting that the juvenile was inexperienced,” writes researcher Gavin Hunt.
Crows who made hooked tools tended to hang on to them, and when Hunt and Russell Gray assembled a collection of 15 hooks, they got most of them by scaring off crows who had set their tools down for a moment. They also got two tools that crows had dropped and two that were left on a feeding table. The hooks are small but useful, and the crows consistently use the hooked end and not the straight end in their foraging (as evidenced by signs of wear).
Gavin Hunt, chronicler of the tool-using exploits of New Caledonian crows, says they appear to be “the only non-human species that manufacture and use hooked instruments.” He goes on to demolish claims that chimpanzees have been seen to use hooked sticks to reach for figs—of those three chimps, only one used a stick with a hooked aspect to it, and half the time he held it by the wrong end! (This is the kind of statement that can only result in the discovery of chimps somewhere using hooks incessantly—to reach fruit, to scratch their backs, to crochet doilies with the motto Crows Are Birdbrains cross-stitched around the rim.)
Throwing the first stone
Two ornithologists were clambering around cliffs in eastern Oregon looking for ravens’ nests. They climbed up to one and examined the six baby ravens they found within. When they exited, they were greeted by angry raven parents, who swooped at them furiously. As the ornithologists descended the cliff, a rock “the size of a golf ball” hurtled past. They thought a raven had accidentally kicked it loose until they looked up and saw a raven on top of the cliff with another rock in its bill. As they watched, the raven tossed it at them. They cowered against the cliff and watched in astonishment as the raven threw six more rocks, hitting an ornithologist on the leg. They returned later in the day, hoping to photograph this behavior, but the ravens were out of rocks and could only throw grit. The next year they came back to the site, but for some reason no ravens had nested in that spot.
The mad genius prisoner
A group of captive bald eagles got in the habit of throwing things, and it wasn’t pretty. They threw a ring at a human, they threw rocks at crickets, they threw rocks at a turtle. I can understand that they might have blamed humans for their situation, and crickets could be edible, but surely the turtle was blameless? One of these eagles gripped a rock in his talons and used it to strike crickets and a scorpion; it also gripped a stick and used it to beat on that poor turtle.
I like eggs, but I don’t know how to fix them
Egyptian vultures have become TV stars because of their habit of breaking open ostrich eggs by throwing stones at them. An Egyptian vulture who finds an unprotected egg in an area where there are no suitable rocks to throw will fly off and fetch one. Other vulture species in the area don’t do this, although they are delighted to eat an ostrich egg that has already been broken.
Researchers kidnapped baby Egyptian vultures and raised them in captivity to find out how they learn to do this, specifically whether they copy other vultures who know how. A previous captive had been offered an ostrich egg, but instead of breaking it, had incubated it, leading to the suggestion that eating them was a cultural tradition. When the young vultures were presented with (fake, fiberglass) ostrich eggs, they were intrigued, but the thought of breaking the eggs or throwing things at the eggs did not occur to them. Researchers began giving them chicken eggs to eat, and these the young vultures liked. They soon figured out that they could pick up and throw these little eggs.
When they were a year old, they were offered fake ostrich eggs again, and they were interested, “suggesting that they were generalizing about shapes.” But they didn’t do much about it, even though there were stones handy. The researchers then gave one of the vultures a hen’s egg cracked into a fake ostrich egg shell. Eureka! The nex
t time the bird was given an ostrich egg, it immediately threw rocks at it. It didn’t manage to hit the egg until its fifth throw, but after seven more tries it scored nine hits in a row.
The researchers concluded that wild vultures learn to break ostrich eggs, but not by copying other vultures. They argue that the critical thing is for the vulture to “experienc[e] an [o]strich egg as food.” Only then will they throw stones at it. Egyptian vultures like to throw things: they throw small eggs to break them (in the wild, pelican and flamingo eggs), and one has been seen throwing stones at a tortoise. From throwing eggs to throwing things at eggs is not a great leap.
Nests, burrows, and dens
Building a place to live would seem to be related to tool use, since lots of object manipulation and material skills are involved. Why would it be tool use if you pick up a rock to throw at an egg, and not if you use it as part of the wall in a chic little two-room bungalow burrow you are building in the sand near a coral reef, like the yellowhead jawfish? But nest and burrow building is so obviously under so much genetic control that it has seldom been considered indicative of intelligence of any kind.
Gorillas, chimpanzees, bonobos, and orangutans all build nests to sleep in at night, and monkeys don’t. (But among the lowly prosimians, bushbabies, mouse lemurs, and aye-ayes build sweet little nests.) Usually any behavior that great apes do and monkeys don’t is considered to be a big deal, but there’s a hitch here. We don’t do it. Or do we—can we compare building beds and even houses with making a nest of branches?
Barbara Fruth and Gottfried Hohmann argue that nest building deserves closer examination. “With some exceptions…. nest construction at night and nest leaving in the morning became more the curfew times of behavioral observation than a topic of research itself.” In other words, when the ape began to build a nest, weary scientists thought with relief of quitting for the day, not of compiling information about nest building.
Fruth and Hohmann studied nest building in chimpanzees and bonobos. They found that nests, which take a few minutes to make, include three elements: a solid frame, a central “mattress,” and a lining made of leaves and twigs. It’s not well understood how young chimpanzees and bonobos develop this behavior. They have an innate urge to make a nest, and hand-raised infants make nests out of blankets, sofa cushions, canvas bags, and whatever comes to hand. Observation of young wild chimpanzees hints that they develop their skills with practice. During the day, young chimpanzees and bonobos make play nests, and their technique is often poor.
Fruth and Hohmann propose the hypothesis that not only should nest building be considered tool use, “but it is also the original tool that led to the mental and physical ability to use the tool we see today.” They postulate that the original ancestors of all great apes (including us) must have been nest builders. Perhaps nest building originated with feeding nests, when apes bend branches to make a convenient sitting place while they pillage a fruiting tree. Groups of nests, when apes build nests close together, might serve as an information center. Fruth and Hohmann also make the touching suggestion that nests may help apes sleep better.
In the Denver Zoo, the gorillas make ground nests. Ernie was a superb craftsman, and his work was much in demand by Bibi, who liked his handiwork so well that she regularly kicked him out and took his nest. Soon, whenever Ernie saw Bibi heading his way with that “I feel like a nap, buster” look in her eye, he would jump out of his nest, pick it up, and carry it to a safer spot.
I think I see what you were getting at
Nests have been referred to as frozen behavior, since they record a sequence of acts and decisions. Most of those acts arise innately, and most of those decisions arise when the animal compares what it is building to an innate template—a vision of the palace it was born to build. Birds raised by humans, birds who have never seen a nest, are for the most part perfectly able to build an excellent nest, given the proper materials. If not, they will improvise, like a peach-faced lovebird of my acquaintance who happily sliced a window blind into useful strips.
Nests are vital to the survival of baby birds. It makes sense that birds need to be born knowing how to perform such a complex, critical task. But learning creeps in. Nicholas and Elsie Collias have performed experiments illuminating the development of nest building in the village weaver.
Male village weavers build excellent nests, employing stitches and fastenings that include the loop tuck, the spiral coil, the alternately reversed winding, the half hitch, the overhand knot, and the slip knot. A nest is ovoid, roofed over, with a bottom entrance, an antechamber, and an egg chamber. It is suspended from a branch. The outside is made of long strips the bird tears from palm fronds or tall grass. Inside he installs a ceiling of short broad strips. The male, a good-looking black-and-orange individual, builds his nest in a day. To attract females, he hangs upside down alluringly from the bottom of his nest, flapping his wings and singing. Females like this. (It is a good bet that a guy who builds a house and hangs by his feet in the doorway singing in an attempt to attract a woman who will settle down with him is not a guy with commitment issues.) If a female likes the nest and the bird enough, she moves in and lines the nest chamber with fine soft materials. At this point the male adds a short hanging entrance tube.
Pulling off a project like this requires practice, and young males are eager to get started. Both female and male village weavers, from the moment they leave the nest, love to pick things up and manipulate them. They particularly love to poke and pull pieces of grass through holes. At about 10 weeks, females lose interest, but males remain obsessed.
Collias and Collias took village weavers from the nest at one week, before their eyes had opened, and raised them in bowls lined with cloth. At no time were they allowed nest-building materials to weave with. But they had each other. “It was not uncommon to see one of these deprived birds hold a protesting cage-mate’s wing under one foot on a perch and attempt to ‘weave’ the wing feathers.” If driven off, the obsessed birds would weave their own tail feathers.
Later, these birds with no experience were offered nest materials in a range of colors. They preferred green, and the more they thought about it the more they liked it. In the wild, this causes them to select fresh flexible grasses over brittle dry grasses that are hard to work with. If they were offered actual grasses when they were a year old, they were delighted, but they had a hard time tearing strips. What works is to perch on the base of the grass, bite through an edge of the grass leaf, and then, gripping the grass, fly away in the direction of the tip of the grass, tearing loose a long strip. The young birds couldn’t tear a single strip on the first day. They’d perch in the wrong place, or they’d just grab the tip of the grass and try to fly off, or they’d tear in the wrong direction. They finally figured it out.
On the other hand, Phineas, a village weaver raised in isolation by Dr. Catherine Jacobs, never learned to tear strips. From the time he was six months old, Jacobs supplied him with pretorn strips, which he handled fairly competently. When, at the age of four, he was put in an aviary with other weavers, an aviary where fresh palm fronds to make into strips were delivered daily, he was still unable to tear strips. But Phineas was canny. He stole enough strips from other birds to make a crude nest, and then hijacked a half-built nest and completed it.
After tearing strips, the next step is to weave them into a sturdy vertical ring. The birds from the deprived background had a terrible time with this. In one experimental group, in the first week that they had access to decent materials, three males did not succeed in weaving a single stitch, while three males who had been allowed to mess with grasses to their heart’s content did a fine job. In the second week the deprived birds started weaving strips into the wire frame of the aviary, neglecting a guava bush highly suitable for nesting.
Over the following winter, they had no chance to practice, but in the spring when they were given materials once more, the deprived birds did just as well as anybody. Except for LL, a dep
rived bird who was also bullied by everyone. Whenever he tore a strip of material, someone stole it before he could play with it. This was so constant that LL never learned to weave, let alone make a nest. He still liked to tear strips, and to play with them if he was permitted. He was transferred to an aviary where he was able to improve his social position and stand up to other males, but at the time of his death at the age of nine he had never built a nest.
In the wild, in their first year, young village weavers build crude sloppy things with loose ends and flapping loops, in little “play colonies” away from the adult colonies. Some nests in the play colonies have roofs but no floors.
What do young birds learn that eventually makes them good nest builders? Collias and Collias say it appears to be “what in subjective terminology one would call ‘judgment.’” They learn to use materials of the right dimensions and flexibility; to hold a strip that they are starting to tear with their foot so it doesn’t slip away; to persist in pulling on a strip until it is in place; when to let go of the strip to pull the next section into the right place; and to leave it alone once they have woven it into the right place. (Young birds are strongly tempted to pull it out and do it again.)
Collias and Collias, for some reason, induced one weaver to build a very long entrance tube on his nest. They did this by threading extra long strips around the entrance. He couldn’t stand the dangling strips, so he wove them into an extra-long tube, 30 centimeters long instead of the usual 5 to 10 centimeters. Even though the researchers kept their hands off, all his subsequent nests had long entrance tubes, some even longer than 30 centimeters. “It would seem that the male develops a mental picture of the sort of nest to build, based on his experience,” they write.
Becoming a Tiger: The Education of an Animal Child Page 29