Animal Behaviour

I

Introduction

Animal Behaviour, the way different kinds of animals behave, which has fascinated inquiring minds since at least the time of Plato and Aristotle. Particularly intriguing has been the ability of simple creatures to perform complicated tasks—weave a web, build a nest, sing a song, find a home, or capture food—at just the right time with little or no instruction. Such behaviour can be viewed from two quite different perspectives, discussed below: either animals learn everything they do (from “nurture”), or they know what to do instinctively (from “nature”). Neither extreme has proved to be correct.

II

Nurture: The Behaviourists

Until recently the dominant school in behavioural theory has been behaviourism, whose best-known figures are J. B. Watson and B. F. Skinner. Strict behaviourists hold that all behaviour, even breathing and the circulation of blood, according to Watson, is learned; they believe that animals are, in effect, born as blank slates upon which chance and experience are to write their messages. Through conditioning, they believe, an animal’s behaviour is formed. Behaviourists recognize two sorts of conditioning: classical and operant.

In the late 19th century the Russian physiologist Ivan Pavlov discovered classical conditioning while studying digestion. He found that dogs automatically salivate at the sight of food—an unconditioned response to an unconditioned stimulus, to use his terminology. If Pavlov always rang a bell when he offered food, the dogs began slowly to associate this irrelevant (conditioned) stimulus with the food. Eventually the sound of the bell alone could elicit salivation. Hence, the dogs had learned to associate a certain cue with food. Behaviourists see salivation as a simple reflex behaviour—something like the knee-jerk reflex doctors trigger when they tap a patient’s knee with a hammer.

The other category, operant conditioning, works on the principle of punishment or reward. In operant conditioning a rat, for example, is taught to press a bar for food by first being rewarded for facing the correct end of the cage, next being rewarded only when it stands next to the bar, then only when it touches the bar with its body, and so on, until the behaviour is shaped to suit the task. Behaviourists believe that this sort of trial-and-error learning, combined with the associative learning of Pavlov, can serve to link any number of reflexes and simple responses into complex chains that depend on whatever cues nature provides. To an extreme behaviourist, then, animals must learn all the behavioural patterns that they need to know.

III

Nature: The Ethologists

In contrast, ethology—a discipline that developed in Europe—holds that much of what animals know is innate (instinctive). A particular species of digger wasp, for example, finds and captures only honey bees. With no previous experience a female wasp will excavate an elaborate burrow, find a bee, paralyse it with a careful and precise sting to the neck, navigate back to her inconspicuous home, and, when the larder has been stocked with the correct number of bees, lay an egg on one of them and seal the chamber.

The female wasp’s entire behaviour is designed so that she can function in a single specialized way. Ethologists believe that this entire behavioural sequence has been programmed into the wasp by its genes at birth and that, in varying degrees, such patterns of innate guidance may be seen throughout the animal world. Extreme ethologists have even held that all novel behaviours result from maturation—flying in birds, for example, which requires no learning but is delayed until the chick is strong enough—or imprinting, a kind of automatic memorization discussed below.

The three Nobel Prize-winning founders of ethology—Konrad Lorenz of Austria, Nikolaas Tinbergen of the Netherlands, and Karl von Frisch of Germany—uncovered four basic strategies by which genetic programming helps direct the lives of animals: sign stimuli (frequently called releasers), motor programs, drive, and programmed learning (including imprinting).

IV

Sign Stimuli (Releasers)

Sign stimuli are crude, sketchy cues that enable animals to recognize important objects or individuals when they encounter them for the first time. Baby herring gulls, for example, must know from the outset to whom they should direct their begging calls and pecks in order to be fed. An adult returning to the nest with food holds its bill downwards and swings it back and forth in front of the chicks. The baby gulls peck at the red spot on the tip of the bill, causing the parent to regurgitate a meal. The young chick’s recognition of a parent is based entirely on the sign stimulus of the bill’s vertical line and red spot moving horizontally. A wooden model of the bill works as well as the real parent; a knitting needle with a spot is more effective than either in getting the chicks to respond.

Sign stimuli need not be visual. The begging call that a chick produces is a releaser for its parents’ feeding behaviour. The special scent, or pheromone, emitted by female moths is a sign stimulus that attracts males. Tactile (touch) and even electrical sign stimuli are also known.

The most widespread uses of sign stimuli in the animal world are in communication, hunting, and predator avoidance. The young of most species of snake-hunting birds, for instance, innately recognize and avoid deadly coral snakes; young fowl and ducklings are born able to recognize and flee from the silhouette of hawks. Similar sign stimuli are often used in food gathering. The bee-hunting wasp recognizes honey bees by means of a series of releasers: the odour of the bee attracts the wasp upwind; the sight of any small, dark object guides it to the attack; and, finally, the odour of the object as the wasp prepares to sting determines whether the attack will be completed.

This use of a series of releasers, one after the other, greatly increases the specificity of what are individually crude and schematic cues; it is a strategy frequently employed in communication and is known as display. Most animal species are solitary except when courting and rearing young. To avoid confusion, the signals that identify the sex and species of an animal’s potential mate must be clear and unambiguous (see Courtship below).