One population estimated to comprise 1,000 deer inhabited a 131,000-ha. The social behavior of Ozotoceros closely parallels that of Odocoileus. Even when it was abundant the pampas deer lived in small groups rarely exceeding 5-6 individuals, and it still does so. Most observations are of solitary animals. Groups are fluid in size and composition, the members, especially the males, freely moving from one to another.
Males mix with females throughout the year.
Aggregations of up to 50 or more deer sometimes form on common feeding grounds. During the mating season adult males compete with one another for the estrous females. They thrash vegetation with their antlers and rub the scent glands of their head and face on plants and other objects. Sometimes several males may harry a single doe. There is no evidence of territoriality or of lasting pair or harem formation.