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Discover fascinating animal behaviors like the ostrich's wing-flapping and the Japanese macaque monkeys' potato washing. Learn how stimuli elicit responses and the role of genetics in behavior evolution.
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Animal Behavior • Male ostriches compete for females by flapping their large wings and making hissing noises
Elements of Behavior • Do you wash your vegetables before you eat them? • If so, you have something in common with a troop of Japanese macaque monkeys that live on the Pacific island of Koshima • Many years ago, biologists in Koshima began leaving sweet potatoes on a sandy beach to entice the resident monkeys into the open • The monkeys ate their potatoes with sand still stuck to them • One day, a young female member of the troop dunked her potato into a nearby pool and scrubbed the sand off it with her hand • The young monkey, apparently preferring to eat a washed potato, repeated this technique each day • Soon, another monkey in the troop started to imitate her • Months later, her mother began to copy her, too • Eventually, all troop members came to wash their potatoes in the pool • To this day, the descendants of the monkeys on the island of Koshima wash their sweet potatoes before eating them
Stimulus and Response • The macaque monkeys you just read about were exhibiting a learned behavior • Biologists define behavior as the way an organism reacts to changes in its internal condition or external environment • A behavior can be simple, such as turning your head in the direction of a noise, or complex, such as washing food • Usually, behaviors are performed when an animal reacts to a stimulus • A stimulus (plural: stimuli) is any kind of signal that carries information and can be detected • If you are hungry, your body is providing you with an internal stimulus that might prompt you to eat • The sound of your phone ringing on a Friday night is an external stimulus that might result in your running to answer it!
Stimulus and Response • A single, specific reaction to a stimulus—such as waking up when you hear an alarm—is called aresponse • A behavior may consist of more than one response • For example, a tiger shark might respond to the movements of a potential prey by swimming toward the stimulus, attacking the source of the movement, and swallowing the prey • What stimuli are you responding to right now?
Types of Stimuli • Animals respond to many types of external stimuli, such as light, sound, odors, and heat • However, not every animal can detect all of these stimuli • Humans perceive the world through many senses—including sight, smell, touch, taste, and hearing • Other animals have different senses and may respond to stimuli that you are not equipped to sense • The Mexican bulldog bat, for instance, uses high-pitched sounds, which humans cannot hear, to detect the ripples made by a fish breaking the surface of a lake • Some birds can detect Earth's magnetic field and use it to navigate over complex terrain
How Animals Respond • Because of the differences in animals' sensory abilities, responses can vary greatly • When an animal responds to a stimulus, body systems—including the sense organs, nervous system, and muscles—interact to produce the resultant behavior • Once an animal's senses have detected an external stimulus, that information is passed along nerve cells to the brain • The brain and other parts of the nervous system process the information and direct the body's response • Animals with very simple nervous systems are capable of only simple behaviors, such as moving toward a stimulus or away from it • For example, an earthworm will move away from bright light • Animals with more complex nervous systems, such as frogs, are better equipped to respond with more complicated and precise behaviors
Wing-Lifting Behavior • Moths of the genus Automerisnormally rest with their front wings over their hind wings • If disturbed, the moth will move its front wings to expose a striking circular pattern on its hind wings • As one scientist has suggested, this behavior may scare off predators when they mistake the moth's hind-wing pattern for the eyes of predatory owls
Behavior and Evolution • Animal behavior is as important to survival and reproduction as any physical characteristic, such as teeth or claws • Recall that physical traits develop according to a specific set of genetic instructions • Many behaviors are also influenced by genes • Therefore, some behaviors can be inherited by an animal's offspring • Behaviors, like physical characteristics, may evolve under the influence of natural selection • A behavior that is directed by genes may help an individual to survive and reproduce • For example, the genes that code for behavior of the moth in the figure may help the moth escape predators • Organisms with an adaptive behavior will survive and reproduce better than organisms that lack the behavior • After natural selection has operated for many generations, most individuals in the population will exhibit the adaptive behavior
Innate Behavior • Why do newly hatched birds beg for food within moments after hatching? • How do spiders know how to build their first web? • These animals are exhibiting an innate behavior, also called an instinct, or inborn behavior • Innate behaviorsappear in fully functional form the first time they are performed, even though the animal may have had no previous experience with the stimuli to which it responds • One of the simplest innate behaviors is the suckling of a newborn mammal • Other innate behaviors, such as the weaving of a spider web or the building of hanging nests by weaver birds, can be quite complex • All innate behaviors depend on internal mechanisms that develop as a result of complex interactions between an animal's genes and its environment • Biologists do not yet fully understand just how these kinds of interactions occur
Web Building • Innate behaviors appear in fully functional form the first time they are performed • Because web building is an innate behavior, a spider weaves a web correctly the first time it performs the behavior
Learned Behavior • Animals often live in unpredictable environments, so their behavior must be flexible enough to deal with uncertainty and change • Many animals can alter their behavior as a result of experience • Such changes are called learning • Acquired behavior is another name for learning, because these behaviors develop over time
Learned Behavior • Many animals have the ability to learn • Organisms with simple nervous systems, such as most invertebrates, may learn only rarely • Among a few invertebrates, and many chordates, learning is common and occurs under a wide range of circumstances • In animals that care for their young, for example, offspring can learn behaviors from their parents or other caretakers • Scientists have identified several different ways of learning: • The four major types of learning are: • Habituation • Classical conditioning • Operant conditioning • Insight learning
Habituation • The simplest type of learning is habituation • Habituationis a process by which an animal decreases or stops its response to a repetitive stimulus that neither rewards nor harms the animal • By ignoring a nonthreatening or unrewarding stimulus, animals can spend their time and energy more efficiently
Habituation • Consider the common shore ragworm • This animal lives in a sandy tube that it leaves only to feed • If a shadow passes overhead, the worm will instantly retreat to the safety of its burrow • Yet, if repeated shadows pass within a short time span, this response quickly subsides • When the worm has learned that the shadow is neither food nor threat, it will stop responding • At this point the worm has habituated to the stimulus
Classical Conditioning • When a dog sees its owner approaching with a leash, it may wag its tail and bark, eager to go for a walk • The dog has learned to associate the sight of the leash with a walk • Any time an animal makes a mental connection between a stimulus and some kind of reward or punishment, it has learned by classical conditioning • In the case of the dog and its owner, the stimulus of the leash is associated with a pleasant reward—a brisk walk • Now, think of what happens if a dog tries to attack a skunk • The skunk sprays the dog with a substance that stings and smells awful • In the future, that dog is likely to avoid skunks, because it associates the stimuli of the sight and scent of the skunk with the punishment of its foul spray
Operant Conditioning • Conditioning is often used to train animals • Operant conditioningoccurs when an animal learns to behave in a certain way through repeated practice, in order to receive a reward or avoid punishment • Operant conditioning is also called trial-and-error learning because it begins with a random behavior that is rewarded in an event called a trial • Most trials result in errors, but occasionally a trial will lead to a reward or punishment
Operant Conditioning • Operant conditioning was first described in the 1940s by the American psychologist B. F. Skinner • Skinner invented a testing procedure that used a certain type of box called a “Skinner box” • A Skinner box contains a colored button or lever that, when pressed, delivers a food reward • After an animal is rewarded several times, it learns that it gets food whenever it presses the button or lever • At this point, the animal has learned by operant conditioning how to obtain food
Insight Learning • The most complicated form of learning is insight learning, or reasoning • Insight learning occurs when an animal applies something it has already learned to a new situation, without a period of trial and error • For instance, if you are given a new math problem on an exam, you may apply principles you have already learned in the class in order to solve the problem • Insight learning is common among humans and other primates • In one experiment, a hungry chimpanzee used insight learning to figure out how to reach a bunch of bananas hanging overhead: it stacked some boxes on top of one another and climbed to the top of the stack • In contrast, if a dog accidentally wraps its leash around a tree, the dog is usually unable to free itself
Instinct and Learning Combined • Most behaviors result from a combination of innate ability and learning • Young white-crowned sparrows, for example, have an innate ability to recognize their own species' song • To sing the complete version, however, the young birds must first hear it sung by the adults
Instinct and Learning Combined • Some very young animals, such as ducks and geese, learn to recognize and follow the first moving object that they see during a critical time early in their lives • Usually, this object is their mother • This process is called imprinting • Imprinting keeps young animals close to their mother, who protects them and leads them to food sources • Once imprinting has occurred, the behavior cannot be changed
Instinct and Learning Combined • Imprinting involves both innate and learned behavior • The young animals have an innate urge to follow the first moving object they see, but they are not born knowing what that object will look like • The young animal must learn from experience what object to follow • In fact, the object on which the young animal imprints does not have to be its mother, or even a living organism
Instinct and Learning Combined • Imprinting can occur through scent as well as sight • Newly hatched salmon, for example, imprint on the odor of the stream in which they hatch • Young salmon then head out to sea • Years later, when they mature, the salmon remember the odor of their home stream and return there to spawn
Patterns of Behavior • At this very moment, somewhere in an African grassland, elephants are calling to one another • Elephants communicate with sounds that they use to locate each other across distances more than 2 kilometers away • When they are not calling long-distance, elephants may spar with each other to test their strength or greet each other by wrapping their trunks together • These behaviors are patterns that have evolved in elephants • In this section, you will investigate some common patterns of animal behavior
Behavioral Cycles • The environment is full of natural cycles • Night follows day, seasons change, the moon has phases, the tides rise and fall • Many animals respond to periodic changes in the environment with daily or seasonal cycles of behavior • For example, several species of reptiles and mammals are active during warm seasons but enter into a sleeplike state, or dormancy, during cold seasons • Dormancy allows an animal to survive periods when food and other resources may not be available
Behavioral Cycles • Another type of behavior that is influenced by changing seasons is migration, the periodic movement from one place to another and then back again • Animals that migrate include species of birds, butterflies, and whales • Migration usually allows animals to take advantage of favorable environmental conditions • For example, when birds fly south for the winter, they go to regions where food is more plentiful than in northern areas
Turtle Migration • Each year, between December and June, green sea turtles migrate from their feeding grounds along the coast of Brazil to mate and nest on Ascension, a tiny island more than 2000 kilometers away • Like many animals, sea turtles migrate in response to seasonal changes in their environment
Behavioral Cycles • Behavioral cycles that occur in daily patterns are called circadian rhythms • The fact that you sleep at night and attend school during the day is an example of a circadian rhythm
Courtship • Animal behavior is geared toward reproduction as well as survival • To pass along its genes to the next generation, any animal that reproduces sexually needs to locate and mate with another member of its species at least once • Courtship behavior is part of an overall reproductive strategy that helps many animals identify healthy mates
Courtship • Incourtship, an individual sends out stimuli—such as sounds, visual displays, or chemicals—in order to attract a member of the opposite sex • For example, fireflies flasha distinct series of light signals to indicate their readiness to mate • The musical trill of a tree frog and the sheeplike bleat of a narrowmouth toad are among the many distinctive breeding calls of amphibians
Courtship • In some species, courtship involves an elaborate series of behaviors called rituals • A ritualis a series of behaviors performed the same way by all members of a population for the purpose of communicating • Most rituals consist of specific signals and individual responses that continue until mating occurs • For example, newly paired cranes engage in intense periods of dancing before they mate
Social Behavior • Whenever animals interact with members of their own species, as in courtship, they are exhibiting social behavior • Many animals go beyond courtship in their social behavior and form societies • An animal societyis a group of related animals of the same species that interact closely and often cooperate with one another • It takes the cooperative work of millions of termites, for example, to build a single termite mound
Social Behavior • For some species, membership in a society offers great survival advantages • Zebras and other grazers, for example, band together when grazing • They are safer from predators when they are part of a group rather than when they are alone • Animal societies also use strength in numbers to improve their ability to hunt, to protect their territory, to guard their young, and to fight with rivals if necessary • In wild African dog packs, for instance, adult females take turns guarding all the pups in the pack, while the other adults hunt together for prey
Social Behavior • Often, members of a society are closely related to one another • Related individuals share a large proportion of each other's genes • Therefore, helping a relative survive increases the chance that the genes an individual shares with that relative will be passed along to offspring • Thus, social behavior that helps a relative survive and reproduce improves an individual's evolutionary fitness
Social Behavior • Primates form some of the most complex animal social groups known • Macaque, baboon, and other primate societies hunt together, travel in search of new territory, and interact with neighboring societies • A great deal of what we know about primate societies comes from the work of Jane Goodall, the animal behaviorist, who spent thousands of hours observing chimps in their natural habitat
Competition and Aggression • Some animals have behaviors that help prevent others from using limited resources • Often, such patterns involve a specific area, orterritory, that is occupied and protected by an animal or group of animals • Territories contain resources, such as food, water, nesting sites, shelter, and potential mates, that are necessary for an animal's survival and reproduction • By claiming a territory, an animal keeps others at a distance • If a rival enters a territory, the “owner” of the territory may attack the rival and drive it away • Algae-eating damselfishare notorious for making such attacks • An algae-eating damselfish can distinguish other algae-feeding species from species that do not eat algae • The damselfish chases the other algae-eaters away, but ignores the fish that do not eat algae
Competition and Aggression • When two or more animals try to claim limited resources, such as a territory or food, competition occurs • Many animals, such as the giraffes, use rituals and displays when they compete • During competition, animals may also show aggression, a threatening behavior that one animal uses to gain control over another • For instance, before a pride of lions settles down to eat, individuals may snap, claw, and snarl at one another • The most aggressive members will get to eat their fill of prey • The less aggressive lions will have to wait for their chance to feed
Giraffe Competition • By interwining their long necks, these two giraffes compete for resources on an African savanna • What resources might these giraffes compete for?
Communication • Often, when animal behavior involves more than one individual, some form ofcommunication—the passing of information from one organism to another—is involved • Animals may use visual, sound, touch, or chemical signals to communicate with one another • The specific techniques that animals use depend on the types of stimuli their senses can detect
Visual Signals • Animals with good eyesight often use visual signals involving movement and color • Cuttlefish, for example, have large eyes that are as sophisticated as those of vertebrates • In a matter of seconds, a single cuttlefish can undergo changes in the colors and patterns on its body • Its skin will pucker into bumps and spines, then suddenly become smooth as stone • These visual displays—as fascinating as any computer screen saver—function in defense, hunting, mating, warning, and perhaps other forms of communication that are not yet known
Chemical Signals • Animals with well-developed senses of smell, including insects, fishes, and many mammals, may communicate with chemicals • For example, some animals release pheromones, chemical messengers that affect the behavior of other individuals of the same species, to mark a territory or to signal their readiness to mate
Sound Signals • Animals with strong vocal abilities, including crickets, toads, and birds, communicate with sound • Some animals that use sound have evolved elaborate communication systems • Dolphins, for example, rely mainly on sound signals in the dark and often murky ocean depths where vision is not very useful • Scientists have discovered that bottlenose dolphins each have their own unique “signature” whistle that is used for recognition • The dolphins' whistles function something like your signature on a letter, letting others know who is sending the communication
Language • The most complicated form of communication is language • Languageis a system of communication that combines sounds, symbols, or gestures according to sets of rules about word order and meaning, such as grammar and syntax • Many animals, like dolphins, elephants, and gorillas, have fairly complex ways of communicating • However, outside of experiments in which they were trained by humans, none of those animals have been shown to use language • Only humans are known to use language
