Agonistic behavior of ground squirrels was studied for two years in north-eastern Utah at an elevation of 6,300 feet. The main objective was to determine what role agonistic behavior had in regulating density in a population. All individuals in an unconfined population were trapped I marked I and observed from towers. Detailed data on behavior and density were recorded.
Though loss from a variety of factors occurred throughout the year I agonistic behavior had an important role in regulating the population at least twice during the year. In spring some squirrels I usually yearling males and late emerging yearling females, were unable to establish territories. Breeding density was thus limited. In summer an overproduction of young was greatly reduced through aggression in, and movement of, young squirrels. This appeared to be the more important to the population in terms of numbers lost.
Agonistic behavior was influenced by density, visibility, movement, and intrusion of nonresidents on areas; by age, sex, and aggressiveness of squirrels; and by time of day and season--all probably warrant consideration in any study of agonistic behavior
