Determinants of social dominance in eastern gray squirrels ( Sciurus carolinensis): a quantitative assessment

Abstract

This study, conducted from January 1979 to August 1981 at the Rachelwood Wildlife Research Preserve, Westmoreland County, Pennsylvania, U.S.A., examined the structure of the dominance hierarchy in a free-ranging population of eastern gray squirrels ( Sciurus carolinensis), using physical attributes and behavioural patterns correlated with social status for groups observed in arena trials. Multivariate statistical analyses (principal components and linear discriminant function analyses) of over 380 agonistic interactions indicated that the primary determinants of dominance were the animals' sex and age, and that the frequency of display of key agonistic behaviour patterns could predict an individual's age (i.e. dominance) status, with over 94% accuracy. Non-parametric analyses of variance (Kruskal-Wallis and Jonckheere-Terpstra procedures) showed that adults significantly out-ranked immatures of both sexes. No significant differences in status were found in comparisons between immature animals and among adults, although average rank consistently increased with age among adults. Within sex/age groups, weight of the animals did not significantly influence status. These results support those determinants of dominance proposed in several earlier studies of gray squirrel social behaviour and behavioural ecology.