Читать книгу The Behavior of Animals - Группа авторов - Страница 83

What determines when a particular behavior will occur, how long it will continue, and what behavior will follow it? One can imagine that all an animal’s behavior systems are competing with each other for expression, perhaps in a kind of free-for-all. For example, if the level of causal factors for eating is very high, the hunger system will inhibit other systems and the animal will eat. As it eats, the causal factors for eating will decline while the causal factors for other behaviors, say drinking, will become higher than those for eating and the animal will change its behavior. If a predator approaches, the escape system will be strongly activated, which will inhibit eating and drinking, and the animal will run away. And so on.

Unfortunately, as attractive as this account appears, it is clearly an oversimplification of reality. Perhaps its most serious shortcoming is that if there were a real free-for-all and only the most dominant behavior system could be expressed, many essential but generally low-priority activities might never occur. If a hungry animal never stopped to look around for danger before the predator was upon it, it would not long survive. Since most animals do survive, this must imply that the rules for behavioral change are more complex than the “winner take all” model. Lorenz (1966) has compared the interactions among behavior systems to the working of a parliament that, though generally democratic, has evolved special rules and procedures to produce at least tolerable and practicable compromises between different interests. The special rules that apply to interactions among behavior systems have only begun to be studied, but a few principles are beginning to emerge.

One important mechanism for behavioral change arises from the fact that most behavior systems are organized in such a way that “pauses” occur after the animal has engaged in a particular activity for a certain time. The level of causal factors for the activity may remain very high, but during the pause other activities can occur. For example, in many species, feeding occurs in discrete bouts; between bouts there is an opportunity for the animal to groom, look around, drink, and so on. It appears that the dominant behavior system (in this case, the hunger system) releases its inhibition on other systems for a certain length of time. During the period of disinhibition, other behavior systems may compete for dominance according to their level of causal factors or each system may, so to speak, be given a turn to express itself. McFarland (1974) has compared these kinds of interactions among behavior systems with the “time-sharing” that occurs when multiple users share the same computer system.

A striking example of this sort of behavioral organization is the incubation system of certain species of birds. Broody hens sit on their eggs for about 3 weeks. Once or twice a day, the hen gets off the eggs for about 10 minutes. During this interval she eats, drinks, grooms, and defecates. The proportion of the 10 minutes spent eating will vary depending on the state of her hunger system, but even 24 hours of food deprivation does not change the pattern of leaving the eggs (Sherry et al. 1980).

Another type of mechanism for behavior change depends upon the reaction of an animal to discrepant feedback. A male Siamese fighting fish, for example, will not display as long to its mirror image as to another displaying male. This is because the behavior of the mirror image is always identical to the behavior of the subject, but identical responses are not part of the “species expectation” of responses to aggressive display (Bols 1977). These mechanisms, and undoubtedly many others, all interact to produce the infinite variety of sequences of behavior characteristic of the animal in its natural environment.