Social behavior of the collared peccary was studied on the lower, eastern slopes of the Mazatzal Mountains, Arizona. The social unit in this species is a cohesive herd, in which small inter-individual distances are maintained. Two conspicuous acts, one olfactory and one auditory, functioned to maintain close spacing. Social interactions were brief but tended to synchronize the activities of animals and also to bring them closer together. Amicable and neutral actions occurred far more frequently

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... than agonistic interactions. Most agonistic behavior did not involve physical contact. Cooperative nursing, predator defense, and feeding occurred; all adults were tolerant of young, and males showed little overt competition over estrous females. The absence of sexual dimorphism, the 1:1 sex ratio within social groups, and the small, precocial litters in this species suggest an evolutionary history of pronounced sociality. Kin selection possibly was important in the evolution of social behavior in peccaries. The Artiodactyla are an appropriate group for comparative study of social behavior because they occupy a wide variety of habitats and show a broad range of social organizations. Within the order, plains-living forms have been studied more than forest-dwellers, and members of the Bovidae have received more attention than other families. However, as Geist (1977) stated recently, important exceptiOJlS to generalizations from bovids may occur in the families Suidae and Tayassuidae. We report here data on social behavior and organization of the collared peccary, Tayassu tajacu, a small-bodied neotropical ungulate that, since the Pleistocene, has extended its range into North America. In Arizona and Texas, where they have been studied most intensively, collared peccaries live almost exclusively in herds of about 5 to 15 individuals (Bigler