Why Cockatoos Are Left-footed
And other new explanations for some of the animal kingdoms's more puzzling behaviors
- Doug Stewart
- Oct 01, 1996
Animal-behavior scientists are no longer content simply to describe what animals do and where and when they do it. The main question now is why: Why do spiders commit suicide? Why do puppies bow? As researchers look more closely at the elaborate dances of prey and predator, brother and sister, seducer and seduced, they are finding a world of complexity rarely suspected by old-school naturalists. The modern investigators' tools, of course, come from the six-decade-old science of ethology--which emphasizes observation of animal behavior under the most natural conditions possible. With each new revelation, the gulf between the clever, unpredictable behavior of humans and the supposedly routine, almost mechanical actions of other animals seems to shrink just a bit. Take, for example, any one of the items in the following roundup of new research.
Bow to Your Partner
Ever wonder if half-grown puppies nipping and snarling at each other were playing or fighting? Puppies evidently wonder the same thing. Cognitive ethologist Marc Bekoff of the University of Colorado has found that to keep roughhousing from being misinterpreted, young dogs, wolves and coyotes extend their front legs beseechingly for a second or two, shoulders low, hind quarters high, before bounding back into action. The gesture appears for all the world to be a bow. It signals, "Oops, sorry about that. Can we keep playing?"
"Bowing can be used to initiate play-- I want to play with you'--and it can maintain play-- Despite what I just did, I still want to play with you,'" Bekoff says. The animals bow most often, he has found, either just before or just after they bite their partners. A little nip is playful; a bigger chomp is serious business. An immature canine may bite down harder than it intended--hence the bow, says Bekoff. He believes bowing is part of a suite of behaviors that an animal learns. "Play is a way to exercise, to socialize, to learn what it's like to be a dog or a wolf or a coyote," he says, "but it's also a way to learn specific communication skills."
The Case Of the Left-Footed Cockatoos
About 90 percent of humans are right-handed, and until recently, scientists thought our species alone had such a pronounced preference for one side over the other. But recent studies have turned up evidence of "handedness" in some other species. And now University of Michigan biologist John W. Pepper reports that a species of cockatoo, a kind of parrot, appears to be 100-percent left-footed.
Pepper studied an endangered population of glossy black cockatoos on Australia's Kangaroo Island. The birds perch in casuarina trees, where they spend most of their waking hours feeding on small seed cones. "They always hold the seed cone with the left foot while standing on their right foot and ripping the cone apart with their bill," says Pepper. His research team observed 27 cockatoos devour 1,382 seed cones over several months. Only once did a bird handle a cone with its right foot. "That particular bird was young," Pepper says. "She may just have been goofy."
Biologists have speculated that the human preference for one side or the other is linked to our brain's specialization for either speech or fine motor ability, if not both. And wouldn't you know it: Cockatoos are skillful vocal mimics, and they are remarkably adroit, so to speak, with those big left feet.
Roaring in Harmony
The roar of a mother lion guarding newborn cubs may be a bone-chilling sound to most other animals, but to an unattached male lion, oddly enough, it can sound like a come-on. Single males passing through a territory often kill a female's cubs, the better to force her back into the pool of available mates. "Females will fight to the death with males to protect their cubs," says biologist Jon Grinnell of Ohio's College of Wooster. But a chorus of female roars, he and Karen McComb of the University of Sussex have found, can make all the difference.
Working in Tanzania's Serengeti National Park, Grinnell and McComb made tape recordings of female lions in groups of one, two and three. They then hid their loudspeaker in a tree and played back various roars at dusk at levels as high as 100 decibels. Males in the vicinity apparently paid close attention to what they heard.
"If a single male hears three females roaring, he's the least likely to approach. If a group of males hears one female, they won't be deterred at all; in some cases, they will literally run toward the sound." An additional factor is age. "Young males approach more quickly," Grinnell says. "They're more foolhardy, you might say."
By roaring in unison, Grinnell and McComb concluded, mother lions get the benefits of fighting without the costs. For long-distance deterrence, harmony makes all the difference.
Baby-sitting skills don't spring to mind as important survival tools. But among cotton-top tamarins, how capably a juvenile cares for a baby brother or sister may distinguish those most likely to succeed from the also-rans.
Gretchen Achenbach recently studied the behavior of families of captive tamarins at the University of Wisconsin, where she is a doctoral candidate in psychology. Unlike most other primates, cotton-top tamarins, squirrel-sized monkeys native to Colombia, live in family groups led by a monogamous breeding pair. The arrival of a newborn immediately puts an end to the family harmony, but tamarin siblings don't act up out of jealousy, Achenbach says. They just want to help. "The mothers nearly always give birth to twins, which together can be 20 percent of their mother's weight at birth," she explains. For the mother, carrying around the fast-growing twins day and night is quickly out of the question. The youngsters need someone else to cling to for safety and warmth, so other family members, including older siblings, offer their fur.
The volunteers are not simply being goody-goodies. Self-interest plays a role. "Tamarins that have not had experience in the family group usually fail as parents," Achenbach says. An inexperienced parent can easily drop an infant during a hand-off (a disaster when you live in a tree). "If it's important for tamarins to learn how to care for infants, it may be in their own best interests to care for their younger siblings."
This desire to help out with newborns is what leads to familial friction, Achenbach has concluded. "On the day of the birth, the juveniles are touching the babies, tugging at the parents, following them around," she says. "There's a rise in conflict with the parents right away." Though tamarins rarely fight, adults will take a swat at meddlesome juveniles. As for sibling rivalry, most of what Achenbach observed seemed to be not over who got mom's attention but rather over who got to carry junior.
Don't Eat Me! Eat Each Other!
When a minnow is attacked, a chemical called an alarm pheromone leaks into the water from its punctured skin, warning nearby minnows to take off and hide. Now a research team led by biologist R.J.F. Smith at the University of Saskatchewan has proved that the chemical alarm of a fathead minnow attracts more predators, and quickly. Smith believes this is a case of the minnow making the best of a bad situation. One of the fish's few options, Smith says, "is calling in another predator that may interfere with its capture and let it get away."
Although other minnows react instinctively to a peer's alarm, they evidently learn only from experience to link the alarm to whatever threat tripped it. (Northern pike and beetles are among the usual culprits.) Some minnows live in streams with no predatory fish and haven't learned to be afraid of them. "But if one time they smell their own alarm pheromone at the same time that they see or smell a pike," says Smith, "they're scared of pike for months afterward."
The chemical can persist long after its creator has been consumed. "The pheromone goes right through juvenile pike and comes out in its droppings," Smith says. "Minnows will sense the pheromones in the droppings and learn to avoid pike." In tank tests, he reports, pike took to defecating at one end and lurking in wait at the other for unsuspecting minnow prey.
When Love Is All-Consuming
In pursuit of a mate, males of many species make sacrifices. The Australian red-backed spider, a kind of black widow, sometimes makes the ultimate sacrifice. "What's amazing is that he appears to do it voluntarily," says Darryl Gwynne, a biologist at the University of Toronto. "During the last throes of copulation, he does a little somersault straight into the female's jaws." The two start out facing in the same direction, the male on top of the female. Once they are attached (the relevant parts are in her abdomen and next to his jaws), the male executes a headstand and flops over to place his stomach near her mouth. With admirable resolve, he keeps copulating as the female consumes him.
There are good reasons for this behavior--in Darwinian terms, at any rate. In an experiment, graduate student Maydianne Andrade, now at Cornell University, let female spiders in Gwynne's lab mate with two males in sequence. She then checked the paternity of the fertilized eggs. "I found that the longer a male copulated, relative to his rival, the more eggs he fertilized," she says. Males that are consumed copulate longer than other males--and sire more offspring than their still-breathing rivals. All the males mate only once anyway, whether or not they survive.
More common than the males that give their all to love are those that let their mates nibble on nonessential body parts. The male sagebrush cricket, for example, lets the female munch on a pair of vestigial hind wings. In such cases, courtship feeding is largely a ruse to occupy a female while the male does his thing. In other cases, mate-feeding may nourish the male's future offspring.
One species of male katydid secretes a big, gelatinous wad of jelly. Attached to it is a small packet of sperm. During copulation, the male inserts one end of the sperm packet into the female. She then reaches around to feed on the jelly (without it, she would yank out the sperm packet and feed on that instead). "We found that the food contributes to bigger eggs and to offspring that survive longer," Gwynne reports. "It's really a form of parental care. It enables the male to make better babies--his babies."
When Mockingbirds Say "Hew"
Probably only a scientist could be fascinated by mockingbirds' use of the call "hew." After all, not only are the birds able to imitate the songs of dozens of other bird species, they also can mimic noises ranging from barking to the squeaking of a wheelbarrow. But plain old "hew"--a sound of aggression that the birds do not use in their songs--grabbed the attention of psychologist Cheryl Logan of the University of North Carolina. She noticed that members of mated pairs often hew to one another. "It clued me in to the fact that there was a lot of sexual conflict among pairs," she says.
Observing the birds in the wild, Logan discovered in recent years that a drop in hew exchange was strongly associated with the onset of renesting. In other words, when a pair was ready to renest, the birds stopped squabbling.
Now comes a new set of related findings. To appreciate them, one has to know that mockingbirds are what scientists call "socially monogamous." The birds pair up, but then both male and female sometimes seek other partners too. Logan recently found that when a male mockingbird wants a second mate--usually during the incubation period of his first nest--he sometimes sings up a storm to attract new females. His first mate, meanwhile, may have ways of thwarting the new courtship, including using her own hewing. "We think that even before the second mate shows up, the first mate tries to stop his singing," says Logan. Not only that, a male that sings a lot while his mate incubates also sometimes attacks her while she is off the nest. Why? "That's still a puzzle," says Logan. The attacks may be his preemptive attempt to stop his first mate from interfering with singing aimed at attracting a new mate. Just the sort of enigma that could one day shed light on our own human behavior.
Massachusetts journalist Doug Stewart wrote about new discoveries in animal flight for the February/March issue.