Animal Communication
Animal Communication
Only through communication can one animal influence the behavior of another. Compared with the enormous communicative potential of human speech, however, nonhuman communication is severely restricted. Animals may communicate by sounds, scents, touch, and movement. Indeed any sensory channel may be used, and in this sense animal communication has richness and variety.
Unlike our language, which is composed of words with definite meanings that may be rearranged to generate an almost infinite array of new meanings and images, communication of other animals consists of a limited repertoire of signals. Typically, each signal conveys one and only one message. These messages cannot be divided or rearranged to construct new kinds of information. A single message from a sender may, however, contain several bits of relevant information for a receiver.
The song of a cricket announces to an unfertilized female the species of the sender (males of different species have different songs), his sex (only males sing), his location (source of the song), and social status (only a male able to defend the area around his burrow sings from one location). This information is crucial to the female and accomplishes a biological function. But there is no way for the male to alter his song to provide additional information concerning food, predators, or habitat, which might improve his mate’s chances of survival and thus enhance his own fitness.
Chemical Sex Attraction in Moths
Mate attraction in silkworm moths illustrates an extreme case of stereotyped, single message communication that has evolved to serve a
single biological
function: mating. Virgin female
silkworm moths have special glands
that produce a chemical sex attractant
to which males are sensitive. Adult
males smell with their large bushy
antennae, covered with thousands of
sensory hairs that function as receptors
(Figure 38-22). Most of these receptors
are sensitive to the chemical attractant bombykol (a complex alcohol named
after the silkworm Bombyx mori) and
to nothing else.
To attract males, females merely sit quietly and emit a minute amount of bombykol, which is carried downwind. When a few molecules reach a male’s antennae, he is stimulated to fly upwind in search of the female. His search is at first random, but, when by chance he approaches within a few hundred yards of the female, he encounters a concentration gradient of the attractant. Guided by the gradient, he flies toward the female, finds her, and copulates with her.
In this example of chemical communication the attractant bombykol, a pheromone, serves as a signal to bring the sexes together. Its effectiveness is ensured because natural selection favors the evolution of males with antennal receptors sensitive enough to detect the attractant at great distances (several miles). Males with a genotype that produces a less sensitive sensory system fail to locate a female and thus are reproductively eliminated from the population.
Language of Honey Bees One of the most sophisticated and complex of all nonhuman communication systems is the symbolic language of bees. Honey bees are able to communicate the location of food resources when these sources are too distant to be located easily by individual bees. They communicate by dances, which are mainly of two forms. The form having the most informational richness is the waggle dance (Figure 38-23). Bees most commonly execute these dances when a forager has returned from a rich source, carrying either nectar in her stomach or pollen grains packed in basketlike spaces formed by hairs on her legs. The waggle dance is roughly in the pattern of a figure-eight made against the vertical surface on the comb inside the hive. One cycle of the dance consists of three components: (1) a circle with a diameter about three times the length of the bee, (2) a straight run while waggling the abdomen from side to side and emitting a pulsed, lowfrequency sound, and (3) another circle, turning in the opposite direction from the first. This dance is repeated many times with the circling alternating clockwise and counterclockwise.
The significance of the bee dances was discovered in 1943 by German zoologist Karl von Frisch, one of the recipients of the 1973 Nobel Prize. Despite detailed and extensive experiments by von Frisch and others that supported his original interpretations of the honey bee dances, the experiments have been criticized, especially by American biologist Adrian Wenner, who suggests that the correlation between dance symbolism and food location is accidental. He argued that foraging bees bring back odors characteristic of the food source, and that recruits are stimulated by dance to search for flowers bearing those odors. Wenner, with P. H. Wells, has reviewed his studies as a scientific autobiography and polemic (Anatomy of a controversy: the question of a language among bees, 1990, Columbia University Press). Wenner and Wells’ assertions have generated strong controversy and have stimulated more rigorously controlled research on the bee dances. Recently, researchers have constructed a robot bee that can be moved through the waggle dance while producing the dance song with vibrating metal “wings.” When operated in a hive, the computer-directed robot successfully recruited attending bees to visit preselected food dishes outside the hive that had never been visited previously. These experiments provide convincing evidence that the bee dances do communicate both direction and distance information to foraging bees.
The straight, waggle run is the important informational component of the dance. Waggle dances are performed almost always in clear weather, and the direction of the straight run is related to the position of the sun. If the forager has located food directly toward the sun, she will make her waggle run straight upward over the vertical surface of the comb. If food was located 60 degrees to the right of the sun, her waggle run is 60 degrees to the right of vertical. We see then that the waggle run points at the same angle relative to the vertical as the food is located relative to the sun.
Distance of the food source is also coded into bee dances. If the food is close to the hive (less than 50 m), the forager employs a simpler dance called the round dance. The forager simply turns a complete clockwise circle, then turns, and completes a counterclockwise circle, a performance that is repeated many times. Other workers cluster around the scout and become stimulated by the dance as well as by the odor of nectar and pollen grains from flowers she has visited. The recruits then fly out and search in all directions but do not stray far. The round dance carries the message that food is to be found in the vicinity of the hive.
If the food source is farther away, round dances become waggle dances, which provide both distance and directional information. The tempo of the waggle dance is related inversely to the food’s distance. If the food is about 100 m away, each figure-eight cycle lasts about 1.25 seconds; if 1000 m away, it lasts about 3 seconds; and if about 8 km (5 miles) away, it lasts 8 seconds. When food is plentiful, the bees may not dance at all. But when food is scarce, the dancing becomes intense, and other workers cluster around the returning scouts and follow them through the dance patterns.
Communication by Displays
A display is a kind of behavior or series of behaviors that serves a communicative purpose. The release of sex attractant by the female moth and the dances of bees just described are examples of displays; so are alarm calls of herring gulls, songs of the whitecrowned sparrow, courtship dances of the sage grouse, and “eyespots” on the hind wings of certain moths that are exposed quickly to startle potential predators.
The elaborate pair-bonding displays of blue-footed boobies (Figure 38-24) are performed with maximum intensity when the birds come together after a period of separation. The male at right in the illustration is sky pointing: the head and tail are pointed skyward and the wings are swiveled forward in a seemingly impossible position to display their glossy upper surfaces to the female. This display is accompanied by a highpiping whistle. The female at left, for her part, is parading. She steps with exaggerated slow deliberation, lifting each brilliant blue foot in turn, as though holding it aloft momentarily for the male to admire. Such highly personalized displays, performed with droll solemnity, appear comical, even inane to the observer. Indeed the boobies, whose name is derived from the Spanish word “bobo” meaning clown, presumably were so designated for their amusing antics.
The exaggerated nature of the displays ensures that the message is not missed or misunderstood. Such displays are essential to establish and maintain a strong pair bond between male and female. This requirement also explains the repetitious nature of displays that follow one another throughout courtship and until laying of eggs. Redundancy of displays maintains a state of mutual stimulation between male and female, ensuring the degree of cooperation necessary for copulation and subsequent incubation and care of the young. A sexually aroused male has little success with an indifferent female.
Communication between Humans and Other Animals
One uncertainty in studies of animal communication is understanding what sensory channel an animal is using. The signals may be visual displays, odors, vocalizations, tactile vibrations, or electrical currents (as, for example, among certain fishes). Even more difficult is establishing two-way communication between humans and other animals since the investigator must translate meanings into symbols that the animal can understand. Furthermore, people are poor social partners for most other animals.
Animal Cognition
One of the most fascinating subjects in animal behavior deals with animal intelligence and awareness. Animal cognition is a general term for mental function, including perception, thinking, and memory. Many biologists believe that mental processes of animals may be similar to those of humans. Recent studies on animal cognition with nonhuman primates and African Grey parrots have yielded fascinating results.
In the late 1960s Beatrix and Allen Gardner of the University of Nevada in Reno began using American Sign Language (ASL) to train a chimpanzee named Washoe to communicate with her hands the same way that deaf people do. By age five Washoe could sign 132 words, which she could put into strings forming sentences and phrases. She could answer questions, make suggestions, and convey moods. In one session, when asked what a swan was, Washoe answered “water bird.” Washoe also taught signs to other chimpanzees. At first, signs were used as play but soon the chimpanzees used them to make spontaneous requests to trainers such as “drink,” “tickle,” and “hug.” Similar work has been done with other primates including gorillas, orangutans, and pygmy chimpanzees.
Irene Pepperberg of the University of Arizona has worked for years with an African Grey parrot named Alex. Because parrots can vocalize like humans, Pepperberg was able to communicate with Alex using human vocal language. Over the years Alex learned a number of attributes including colors, shapes, and materials for more than 100 objects. Alex not only can identify objects by colors and shape, but can also distinguish the difference between two objects. Thus, if Alex is given two objects of the same color but one larger than the other, he could state that the difference between them was “size.” Alex can also count and relate to the trainer how many objects of each particular category are present.
Conscious awareness is also part of cognition. Donald Griffin wrote two books suggesting that many animals are capable of self-awareness and can think and reason. The ability of apes, parrots, and other animals to use language-related skills is significant because it tells us about their cognitive abilities and we can begin to communicate with them. The possibility that animals may have thinking processes similar to humans and that they have a conscious awareness has shed new light on animal behavior studies and added new significance to our studies of animals in general. Studies of animal cognition remain highly controversial.
The animal behaviorist Irven DeVore reported how choosing the proper channel for dialogue can have more than academic interest:*
One day on the savanna I was away from my truck watching a baboon troop when a young juvenile came and picked up my binoculars. I knew if the glasses disappeared into the troop they’d be lost, so I grabbed them back. The juvenile screamed. Immediately every adult male in the troop rushed at me—I realized what a cornered leopard must feel like. The truck was 30 or 40 feet away. I had to face the males. I started smacking my lips very loudly, a gesture that says as strongly as a baboon can, “I mean you no harm.” The males came charging up, growling, snarling, showing their teeth. Right in front of me they halted, cocked their heads to one side—and started lip-smacking back to me. They lip-smacked. I lip-smacked, “I mean you no harm.” “I mean you no harm.” It was, in retrospect, a marvelous conversation. But while my lips talked baboon, my feet edged toward the truck until I could leap inside and close the door.
The study of animal communication has made great strides in recent years, buoyed by the assimilation of a wealth of facts and information about communication in many species. The animal world is filled with communication. In recognizing that reasoning and insight are not required for effective, highly organized behavior, we should not conclude that other animals are, as Descartes proclaimed in the seventeenth century, nothing more than machines.
Only through communication can one animal influence the behavior of another. Compared with the enormous communicative potential of human speech, however, nonhuman communication is severely restricted. Animals may communicate by sounds, scents, touch, and movement. Indeed any sensory channel may be used, and in this sense animal communication has richness and variety.
Unlike our language, which is composed of words with definite meanings that may be rearranged to generate an almost infinite array of new meanings and images, communication of other animals consists of a limited repertoire of signals. Typically, each signal conveys one and only one message. These messages cannot be divided or rearranged to construct new kinds of information. A single message from a sender may, however, contain several bits of relevant information for a receiver.
The song of a cricket announces to an unfertilized female the species of the sender (males of different species have different songs), his sex (only males sing), his location (source of the song), and social status (only a male able to defend the area around his burrow sings from one location). This information is crucial to the female and accomplishes a biological function. But there is no way for the male to alter his song to provide additional information concerning food, predators, or habitat, which might improve his mate’s chances of survival and thus enhance his own fitness.
Chemical Sex Attraction in Moths
Mate attraction in silkworm moths illustrates an extreme case of stereotyped, single message communication that has evolved to serve a
 |
| Figure 38-22 Large antennae of a male silk worm moth Bombyx mori; these are especially sensitive tothe sex attractant (pheromone) released by the female moth. |
To attract males, females merely sit quietly and emit a minute amount of bombykol, which is carried downwind. When a few molecules reach a male’s antennae, he is stimulated to fly upwind in search of the female. His search is at first random, but, when by chance he approaches within a few hundred yards of the female, he encounters a concentration gradient of the attractant. Guided by the gradient, he flies toward the female, finds her, and copulates with her.
In this example of chemical communication the attractant bombykol, a pheromone, serves as a signal to bring the sexes together. Its effectiveness is ensured because natural selection favors the evolution of males with antennal receptors sensitive enough to detect the attractant at great distances (several miles). Males with a genotype that produces a less sensitive sensory system fail to locate a female and thus are reproductively eliminated from the population.
Language of Honey Bees One of the most sophisticated and complex of all nonhuman communication systems is the symbolic language of bees. Honey bees are able to communicate the location of food resources when these sources are too distant to be located easily by individual bees. They communicate by dances, which are mainly of two forms. The form having the most informational richness is the waggle dance (Figure 38-23). Bees most commonly execute these dances when a forager has returned from a rich source, carrying either nectar in her stomach or pollen grains packed in basketlike spaces formed by hairs on her legs. The waggle dance is roughly in the pattern of a figure-eight made against the vertical surface on the comb inside the hive. One cycle of the dance consists of three components: (1) a circle with a diameter about three times the length of the bee, (2) a straight run while waggling the abdomen from side to side and emitting a pulsed, lowfrequency sound, and (3) another circle, turning in the opposite direction from the first. This dance is repeated many times with the circling alternating clockwise and counterclockwise.
 |
| Figure 38-23 Waggle dance of the honey bee used to communicate both the direction and distance of a food source. The straight run of the waggle dance indicates direction according to the position of the sun (angles X and Y). |
The significance of the bee dances was discovered in 1943 by German zoologist Karl von Frisch, one of the recipients of the 1973 Nobel Prize. Despite detailed and extensive experiments by von Frisch and others that supported his original interpretations of the honey bee dances, the experiments have been criticized, especially by American biologist Adrian Wenner, who suggests that the correlation between dance symbolism and food location is accidental. He argued that foraging bees bring back odors characteristic of the food source, and that recruits are stimulated by dance to search for flowers bearing those odors. Wenner, with P. H. Wells, has reviewed his studies as a scientific autobiography and polemic (Anatomy of a controversy: the question of a language among bees, 1990, Columbia University Press). Wenner and Wells’ assertions have generated strong controversy and have stimulated more rigorously controlled research on the bee dances. Recently, researchers have constructed a robot bee that can be moved through the waggle dance while producing the dance song with vibrating metal “wings.” When operated in a hive, the computer-directed robot successfully recruited attending bees to visit preselected food dishes outside the hive that had never been visited previously. These experiments provide convincing evidence that the bee dances do communicate both direction and distance information to foraging bees.
The straight, waggle run is the important informational component of the dance. Waggle dances are performed almost always in clear weather, and the direction of the straight run is related to the position of the sun. If the forager has located food directly toward the sun, she will make her waggle run straight upward over the vertical surface of the comb. If food was located 60 degrees to the right of the sun, her waggle run is 60 degrees to the right of vertical. We see then that the waggle run points at the same angle relative to the vertical as the food is located relative to the sun.
Distance of the food source is also coded into bee dances. If the food is close to the hive (less than 50 m), the forager employs a simpler dance called the round dance. The forager simply turns a complete clockwise circle, then turns, and completes a counterclockwise circle, a performance that is repeated many times. Other workers cluster around the scout and become stimulated by the dance as well as by the odor of nectar and pollen grains from flowers she has visited. The recruits then fly out and search in all directions but do not stray far. The round dance carries the message that food is to be found in the vicinity of the hive.
If the food source is farther away, round dances become waggle dances, which provide both distance and directional information. The tempo of the waggle dance is related inversely to the food’s distance. If the food is about 100 m away, each figure-eight cycle lasts about 1.25 seconds; if 1000 m away, it lasts about 3 seconds; and if about 8 km (5 miles) away, it lasts 8 seconds. When food is plentiful, the bees may not dance at all. But when food is scarce, the dancing becomes intense, and other workers cluster around the returning scouts and follow them through the dance patterns.
Communication by Displays
A display is a kind of behavior or series of behaviors that serves a communicative purpose. The release of sex attractant by the female moth and the dances of bees just described are examples of displays; so are alarm calls of herring gulls, songs of the whitecrowned sparrow, courtship dances of the sage grouse, and “eyespots” on the hind wings of certain moths that are exposed quickly to startle potential predators.
The elaborate pair-bonding displays of blue-footed boobies (Figure 38-24) are performed with maximum intensity when the birds come together after a period of separation. The male at right in the illustration is sky pointing: the head and tail are pointed skyward and the wings are swiveled forward in a seemingly impossible position to display their glossy upper surfaces to the female. This display is accompanied by a highpiping whistle. The female at left, for her part, is parading. She steps with exaggerated slow deliberation, lifting each brilliant blue foot in turn, as though holding it aloft momentarily for the male to admire. Such highly personalized displays, performed with droll solemnity, appear comical, even inane to the observer. Indeed the boobies, whose name is derived from the Spanish word “bobo” meaning clown, presumably were so designated for their amusing antics.
 |
| Figure 38-24 A pair of Galápagos blue-footed boobies, Sula nebouxii, display to each other. The male (right) is sky pointing; the female (left) is parading. Such vivid, stereotyped, communicative displays serve to maintain reciprocal stimulation and cooperative behavior during courtship, mating, nesting, and care of the young. |
The exaggerated nature of the displays ensures that the message is not missed or misunderstood. Such displays are essential to establish and maintain a strong pair bond between male and female. This requirement also explains the repetitious nature of displays that follow one another throughout courtship and until laying of eggs. Redundancy of displays maintains a state of mutual stimulation between male and female, ensuring the degree of cooperation necessary for copulation and subsequent incubation and care of the young. A sexually aroused male has little success with an indifferent female.
Communication between Humans and Other Animals
One uncertainty in studies of animal communication is understanding what sensory channel an animal is using. The signals may be visual displays, odors, vocalizations, tactile vibrations, or electrical currents (as, for example, among certain fishes). Even more difficult is establishing two-way communication between humans and other animals since the investigator must translate meanings into symbols that the animal can understand. Furthermore, people are poor social partners for most other animals.
Animal Cognition
One of the most fascinating subjects in animal behavior deals with animal intelligence and awareness. Animal cognition is a general term for mental function, including perception, thinking, and memory. Many biologists believe that mental processes of animals may be similar to those of humans. Recent studies on animal cognition with nonhuman primates and African Grey parrots have yielded fascinating results.
In the late 1960s Beatrix and Allen Gardner of the University of Nevada in Reno began using American Sign Language (ASL) to train a chimpanzee named Washoe to communicate with her hands the same way that deaf people do. By age five Washoe could sign 132 words, which she could put into strings forming sentences and phrases. She could answer questions, make suggestions, and convey moods. In one session, when asked what a swan was, Washoe answered “water bird.” Washoe also taught signs to other chimpanzees. At first, signs were used as play but soon the chimpanzees used them to make spontaneous requests to trainers such as “drink,” “tickle,” and “hug.” Similar work has been done with other primates including gorillas, orangutans, and pygmy chimpanzees.
Irene Pepperberg of the University of Arizona has worked for years with an African Grey parrot named Alex. Because parrots can vocalize like humans, Pepperberg was able to communicate with Alex using human vocal language. Over the years Alex learned a number of attributes including colors, shapes, and materials for more than 100 objects. Alex not only can identify objects by colors and shape, but can also distinguish the difference between two objects. Thus, if Alex is given two objects of the same color but one larger than the other, he could state that the difference between them was “size.” Alex can also count and relate to the trainer how many objects of each particular category are present.
Conscious awareness is also part of cognition. Donald Griffin wrote two books suggesting that many animals are capable of self-awareness and can think and reason. The ability of apes, parrots, and other animals to use language-related skills is significant because it tells us about their cognitive abilities and we can begin to communicate with them. The possibility that animals may have thinking processes similar to humans and that they have a conscious awareness has shed new light on animal behavior studies and added new significance to our studies of animals in general. Studies of animal cognition remain highly controversial.
The animal behaviorist Irven DeVore reported how choosing the proper channel for dialogue can have more than academic interest:*
One day on the savanna I was away from my truck watching a baboon troop when a young juvenile came and picked up my binoculars. I knew if the glasses disappeared into the troop they’d be lost, so I grabbed them back. The juvenile screamed. Immediately every adult male in the troop rushed at me—I realized what a cornered leopard must feel like. The truck was 30 or 40 feet away. I had to face the males. I started smacking my lips very loudly, a gesture that says as strongly as a baboon can, “I mean you no harm.” The males came charging up, growling, snarling, showing their teeth. Right in front of me they halted, cocked their heads to one side—and started lip-smacking back to me. They lip-smacked. I lip-smacked, “I mean you no harm.” “I mean you no harm.” It was, in retrospect, a marvelous conversation. But while my lips talked baboon, my feet edged toward the truck until I could leap inside and close the door.
The study of animal communication has made great strides in recent years, buoyed by the assimilation of a wealth of facts and information about communication in many species. The animal world is filled with communication. In recognizing that reasoning and insight are not required for effective, highly organized behavior, we should not conclude that other animals are, as Descartes proclaimed in the seventeenth century, nothing more than machines.
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