Population Changes and Social Behavior Following Colonization by the Yellow-Bellied Marmot

Abstract

In most years, the population of a colony of yellow-bellied marmots (Marmota flaviventris) was fluid because of dispersal of yearlings and addition of young; the adult population remained relatively stable within any year. Recruitment to the adult population occurred solely from animals born in the colony. Total number of young produced was closely correlated with the number of females of reproductive age; the number of young per female decreased at higher population densities because of a greater percentage of nonbreeding 2-year-old females in the population. There was no density-dependent relationship between numbers and survival of young or between number of yearlings and number of adults. The rate of social interactions was generally highest in June and decreased thereafter. Year-to-year and seasonal variations in rates of social interactions are interpreted in relation to the social structure of the population. Rates of social interaction were not directly correlated with population density. The dispersion of the population increased as the population increased. Adult males attempted to obtain exclusive use of the area and directed most of their agonistic behavior toward other males, both adults and yearlings. Agonistic behavior among females exceeded amicable behavior in only one of the five years of study. The growth of the harem may be possible because of mutual tolerance among females. Play fighting occurred only among yearlings. A complex interaction occurs between the behavioral characteristics of the individual animals and density effects related to the number, age, and sex of the animals.