Read an Excerpt
The Language of Animals
By Stephen Hart
Henry Holt and CompanyCopyright © 1996 Robert Ubell Associates, Inc.
All rights reserved.
"Me Tarzan, you Jane." If the male cuttlefish could speak, this might be his opening line. Although cuttlefish rarely use sound to communicate, the male still has an opening line, and it might translate to the longer, but conceptually simpler, "Me Tarzan. You Tarzan? No? Must be Jane." Cuttlefish and squid communicate using their remarkable ability to control the pigment in their skin. They flash messages in colorful spots, splotches and background color. Cuttlefish add to their unique visual communication certain swimming postures and gestures of their ten tentacles. Along with octopuses, cuttlefish and squid belong to the class Cephalopoda, molluscs like snails, slugs and clams. Cephalopods, mental giants of the mollusc world, manipulate objects with tentacles, swim with jet propulsion, eat with beaks and see with eyes as complex as ours.
Direct connections from the brains of cephalopods to special muscles allow split-second change in skin color by relaxing or contracting chromatophores. These skin-surface cells, filled with red, yellow and black pigments, can change from being spread out to being tightly contracted in a few thousandths of a second. Under the surface layer, white pigment cells and even deeper green cells reflect light when unmasked by contracted chromatophores. Cephalopods can also change their skin texture to enhance communication, raising or smoothing warty-looking bumps. Even though cephalopods appear unable to see colors, they seem to match their surroundings remarkably well.
When not fading into the background, some squid and cuttlefish can create dramatic patterns covering either their whole bodies or only parts of it. In some species, observers have catalogued 31 full-body patterns and calculated a potential repertoire of nearly 300 combinations of full-body patterns, partial-body patterns, skin texture and body posture.
Octopuses remain solitary except when mating, and researchers have so far seen little they would call complex communication among them. But like squids and cuttlefish, octopuses do exhibit color changes based on internal physiological states. Males of some octopus species sport enlarged suckers, used in a "sucker display," presumably designed to communicate their sex. Females of one species develop luminescent cells, circling their beaks like green lipstick, that may attract males.
Jane cuttlefish — like females of any species — won't be satisfied with just any male. She wants a healthy, vigorous Tarzan whose sperm will carry genes that enhance her offspring's chance to survive, mature, and breed again. So she looks for a number of attributes. Size signifies health, of course, but in addition, cuttlefish and squid who swim with their arms erect and their skins flashing apparently look healthy to females.
Cuttlefish and squid make great food — not just as sushi, but to several oceanic predators — so they normally blend into the background with a mottled, cryptic color scheme. But for the male cuttlefish, when it comes to mating, the chance of passing on his genes outweighs the risk of becoming a meal.
Stretching his arms forward, bunched together or arched into a ten-stranded basket, he flashes a striking zebra pattern, signaling his sex. Other cuttlefish nearby get the message. Males return the salute, but females remain mottled. The absence of the male pattern, rather than any distinguishing features of the female's pattern, tells the male her sex. If a male fails to respond with a zebra pattern — perhaps because of illness — other males may mistake him for a female.
All males in a group strut their stuff with a zebra pattern, and most females remain mottled. But if a nearby female changes from her cryptic mottled pattern to a more uniform gray, she's signaling her readiness to mate. Now the competition between males grows intense, in some species escalating into physical contact and biting. Finally, all males but one — usually the largest — literally turn tail and retreat, shifting back to their normal, unisex mottled pattern — behavior that resembles the submissive posture of a dog with its tail between its legs.
After discouraging nearby males with his prowess, the victorious male turns from aggressive to sensitive. He approaches the female and turns from visual communication to tactile, gently stroking her between her eyes and arms. At first, she may indicate her alarm by flashing an acute disruptive pattern. The male calms her by blowing water at her and jetting gently away. He approaches again and again until the female accepts him, literally with open arms. If a boorish rival should attempt to intrude, the mating male again flashes an intense zebra pattern. If he's swimming side by side with the female, he can even display his stripes only on the side of his body facing the intruder. At the same time, he can maintain his sexually suggestive uniform gray on the side facing the female. At last, the pair links arms and begins to mate. Both now adopt the cryptic mottled pattern that attracts least attention.
Squid, which are more social than cuttlefish, also communicate courtship with skin color. They gather in groups of 10 to 30 individuals, but soon break up into courtship parties of one female and two to five males. The largest male attempts to guide the female away from other suitors. The couple engages in precopulatory mutual rocking, jetting gently to and fro together. If the male approaches too closely at this point, the female may streak away. The male follows, and this teasing game can continue for up to an hour at high speed, possibly representing an attempt on the female's part to assess the male's health. Male squid use a zebra stripe not unlike the cuttlefish's to ward off other males. They also exhibit a one-sided smooth silver pattern signifying "keep away." The male only displays this lateral silver pattern to other males, keeping the side facing the female sexually stimulating.
Squid don't embrace to mate. Instead, the male merely tries to attach a small, sticky packet of sperm to the female's body. As he reaches out with the sperm packet, he displays a pulsating pattern of chromatophores. If the packet sticks, the female places it in her seminal receptacle, completing the mating ritual.
The social cephalopods, squids (such as Sepioteuthis sepioidea) and cuttlefish, clearly communicate internal states — readiness to mate, sexual identification and the like. Human equivalents might be blushing, stuttering and shy body postures. Do cephalopods communicate more than sexuality? Some scientists suggest that their full-body patterns also act as nouns and verbs and small spots and patterns as adjectives and adverbs. Posture and movement might add context. "It could be that if Sepioteuthis puts stripe on the side of the body, and then puts golden eyebrows over the top of the eyes, and raises the arms, that it has modified stripe by the golden eyebrows and by the arm raise to mean something more complicated or maybe even different from whatever stripe means by itself," says Jennifer Mather. Mather, a psychologist, studies cephalopod behavior and teaches at the University of Lethbridge, Lethbridge, Alberta. Mather's hypothesis, although intriguing, remains unexplored.
To investigate cephalopod visual communication further, Mather and others would like to "speak" their language. By mimicking the visual cues with a colored model — communicating to the cuttlefish in a sense — researchers could watch for behavior changes and begin to understand their complex communication.
"I would suspect that cephalopods are not going to have a language anything like as complicated as ours by the time we know whether they have a visual language," Mather concludes. "But I suspect we are going to find an interesting communication system when we finally have the time and the energy and the resources to find out."CHAPTER 2
Honeybees provide humans with more than natural sweetener and sayings such as "busy as a bee." They also provide a rare example of an animal communicating information about objects that are not close at hand. Some say that honeybees, as simple as they are, provide the only example of such symbolic communication among nonhuman animals.
While most insects limit their social lives to quick mating, bees and some of their relatives, as well as termites, form societies with division of labor and cooperation. Cooperation in most species requires some kind of communication, and the honeybee dance provides the archetypic example. A single worker bee (all workers are female, by the way) finding a rich source of nectar flies back to the hive. A short time later, dozens of fellow workers make beelines to the nectar site.
How do the recruits find the site? That question has plagued naturalists since Aristotle. In the early 1900s, Austrian biologist Karl von Frisch began to study honeybees in earnest. At first, it appeared to von Frisch that bees merely sought out the odor inadvertently brought back to the hive by scout bees. But he also noted intense activity among returning bees and began watching closely. Those returning from his sugar-water feeding stations near the hive marched in a busy circle on the comb. Those carrying pollen from distant flowers danced a figure eight.
Von Frisch first called these behaviors the nectar dance and the pollen dance. But on further study, he formed a new idea — busy activity of scout bees after returning to the hive communicated more than just excitement or information about food type. By moving his feeding station farther and farther from the hive, he determined that when the station reached 50 to 100 yards from the hive, nectar gatherers began dancing the figure eight pollen dance. This dance, von Frisch concluded, related to distant food sources, not food type.
The bees bustled around in a purposeful manner, buzzing their wings and waggling their abdomens. They would hootchy kootchy in a straight line, then circle back to the beginning — first circling left, then right. Von Frisch observed that the speed of the waggle and the angle of the line communicated both distance and direction to workers crowding around the scout.
On a horizontal hive, a bee can merely crosscut her circle in the direction of the flowers she found so full of nectar. The speed of her waggle and the number of circuits per minute indicate distance from the hive. But most bee hives consist of vertical combs. How does a scout point out the right direction? Instead of indicating direction from the hive, she indicates an angle from the location of the sun. Forty five degrees to the right of vertical means forty five degrees to the right of the sun. Scout bees even manage to account for the apparent movement of the sun throughout the day. One thing bees cannot account for, however, is reorientation of their hive. Bees normally nest in trees, so it makes no sense for them to evolve the ability to account for a rotated hive. But bee researchers can easily rotate a hive in a box so that it opens in a different direction. In that case, the bees become confused and cannot follow the direction information contained in the dance.
Von Frisch's suggestion, that bees have a "language," aroused the skepticism of other scientists, some of whom continue to this day to favor von Frisch's earlier idea that scent alone guides bees. Nonetheless, von Frisch shared the 1973 Nobel Prize, indicating wide acceptance for his bee-communication research.
A crucial test for any communication system is to modify it experimentally. Could we communicate with bees, using their dance to indicate distance and direction of a target the bees had never visited? In 1989, a team of European scientists led by Axel Michelsen of Denmark's Odense University did just that. They built a bee of brass and beeswax with a bit of razor blade to represent the wings. Their robot bee could buzz its wings at the requisite 280 cycles per second, waggle its bottom and dance in a circle. It could even deliver drops of sugar water to the dance watchers.
Using a computer to control the robot, researchers set their robobee to dancing, attempting to illuminate the components of the dance. Dancing a normal waggle dance, the mechanical bee, like any robot, was a bit clumsy. But it got the message across. Some recruits used the information to fly to a target Michelsen had set up in a field. On a different day, Michelsen sent the bees in the opposite direction. Bees found new targets, regardless of wind direction, correctly following the robot's message. Robobee could not have communicated with odor, because it never left the hive. Despite its clumsiness, Michelsen says, "In our work with the robot bee, the dancer never visited any of the places advertised, and yet the bees turn up at the places indicated." After years of research with robot bee experiments and other studies with individually numbered bees, all but a few scientists are now convinced that the dance does indeed communicate distance and direction, just as von Frisch suggested.
But how do bees perceive the dance? Since hives are dark, the workers crowding around a dancer cannot see. Michelsen says research has shown that it is unlikely that bees can feel the hectic dance through their feet. Michelsen suspects bees sense air currents set up by the scout's wagging backside and buzzing wings. The robot bee also moves its wings and abdomen fast enough to mimic natural air currents. By modifying the dance, Michelsen highlighted the wagging portion of the dance as the key to conveying direction. Stereotyped semicircles, returning the bee to the starting point, may help to orient surrounding bees to where the next waggle will occur. Communicating distance proved more difficult for robobee. Michelsen thinks his robot lacked subtlety in conveying cues for distance, perhaps even giving conflicting information. Michelsen's present research consists of investigating how air currents generated by dancing bees convey information.
Other researchers have shown that only a small number of bees, who keep their heads very close to the dancing bee, get the message. Workers farther away must wait their turn to move in close enough to read the dance. Further research has strengthened Michelsen's supposition that bees using their antennae "hear" the air vibrations around the dancing bee. Without both antennae intact and functioning, bees could not interpret the distance and direction information conveyed by the remarkable dance.CHAPTER 3
A porch swing on a summer evening: the hinges creak, crickets trill from the field, the wind sighs gently. Gradually, you become conscious of a vaguely annoying sensation. At first, the high-pitched whine barely registers, but it grows louder and closer. Suddenly, the whine appears right in your ear. To you, the sound communicates irritation, like fingernails on a chalkboard. To the male mosquito, it's a beautiful song — the sound of a female mosquito looking for an evening meal of blood.
Male mosquitoes hear and obey the siren call of the female, flying directly toward the sound. "In fact, you can even attract males with a tuning fork of the proper frequency," notes Marc J. Klowden, a mosquito behaviorist at the University of Idaho. Because the sound comes from the female's beating wings — mosquitoes cannot vary their wing-beat frequency at will — it rises in pitch as the air temperature rises. Male mosquitoes detect sound not with ears, but with their antennae, which resonate only at the particular frequency emitted by the female. "The male mosquito antenna is built like a tiny tree sitting on a very small joystick; the branches pick up the vibrations and cause the underlying joystick to move. Movement of the 'joystick,' called Johnston's organ, is translated into nervous impulses by sensory receptors," Klowden explains. The impulses signal the male mosquito's brain, which interprets the sensation as sound.
Fortunately for mosquitoes, the resonant frequency of the male's antennae also rises with temperature, remaining locked in on the pitch of a female of his species. With the mechanical relationship between the female's signal and the male's response, this sexual communication serves its purpose admirably, producing plenty of mosquitoes — many more than we like.
The symphony of cricket trills gracing grassy fields in many parts of the world arises from an all-male orchestra. Each male advertises his presence and prowess by scratching together the bases of his forewings, which are ridged like tiny washboards. Each stroke creates a single chirp, and the cricket's song consists of a series of chirps called a trill. Like the communications of many males, the trill carries two meanings, a come-hither message for females and a go-away message for competing males.
Excerpted from The Language of Animals by Stephen Hart. Copyright © 1996 Robert Ubell Associates, Inc.. Excerpted by permission of Henry Holt and Company.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.