Animals have been companions to humans since prehistoric times, yet relatively little empirical research has been conducted on the sources of the behavior of these animals. One third to one half of all households in the English-speaking world have pets, and in most cases, these animals are highly valued. The identification of one's pet as a family member is quite prevalentù99 percent of dog or cat owners entering a university veterinary clinic answered affirmatively to a survey question about their pet's status as a family member.

The literature on animals as human companions can be roughly divided into studies on naturally occurring pet ownership and studies in which pets have been introduced as a form of intervention. Neither group of these studies, however, provide much information on causal factors of behavior in companion animals.

A newer group of studies, however, is addressing the issues associated with companion animal behavior. The science that will find its way most frequently into everyday veterinary practice in the future is the study of companion animal behavior. It has been estimated that between 35 and 50 percent of the companion animals that veterinarians euthanize are killed because of aggressive or destructive behavior. While the empirical study of companion animal be

The researchers studied nine social groups, containing 413 monkeys, that had lived for at least several years in small indoor pens, in medium-size in-door-outdoor cages, in large outdoor corrals, or on a small island off the coast of South Carolina. Detailed observations of interactions with other group members were gathered for 145 adult males and females in the nine groups. The frequency of aggressive acts rose slightly in more congested quarters. Openly hostile behavior occurred 1.5 times as often in indoor pens as in open areas on the island. The researchers, however, concluded that the disparity was quite small considering that island monkeys had 6,000 times more available space than those restricted to pens.

Timberlake, W. "Animal Behavior: A Continuing Synthesis." Annual Review of Psychology, 44 (Annual 1993): 675-708.

With respect to the exhibition of aggressive behavior by companion animal, one finding has been that such behavior is more likely to be exhibited when such animals are closer to their home. Further, loose pets have been found to be more aggressive than are unowned stray animals. The most common behavior associated with being bitten by someone else's dog is simply entering the dog's territory when it is running loose. Thus, the c