Dominance in the Florida Scrub Jay

Abstract

Dominance behavior in a color-ringed population of Florida scrub jays [Aphelocoma coerulescens coerulescens] was studied during 6 years of general observations and 2 summers of intensive study of intrafamilial and interfamilial aggression. Encounters were recorded from 21 families of varying size and constituency. The jays are extremely tame, which facilitated watching their normal behavior; these observations were augmented with simple experiments involving the offering of tidbits of food. The Florida scrub jay, a permanently territorial group breeder, exhibits a social dominance structure in which the male breeder dominates all other jays in the family, male helpers dominate all females, and the female breeder mildly dominates female helpers. Juveniles, subordinate to all other family members, seem to establish a hierarchy among themselves through investigative encounters during their 1st summer. Whenever 2 or more male helpers coexist in a family, a hierarchy exists between them. Usually the dominant male helper is the first to depart and pair when a breeding opportunity develops. Dominant male helpers occasionally establish a new territory by gradually usurping a portion of their parents'' territory. Although dominance within the jay families is clear, aggressive conflicts are rare. This contrasts sharply with the frequency of boundary disputes between neighboring families. Involvement in interfamilial aggression, measured by summoning jays to playbacks of territorial scolding, is not directly correlated with rank in the family hierarchy, in that breeding females respond more quickly than their male helpers. During brief visits to a neutral feeding area, jays from different families often forage within inches of each other with almost no conflict. Intrafamilial dominance-subordinance relationships are viewed as an early behavioral modification associated with the evolution of the helper system in the Florida scrub jay. Through dominance, family members establish their actual, or potential, reproductive positions in the population while deriving the benefits of living in a family group. Breeding males reduce the threat of cuckoldry or loss of territory by dominating their male helpers. The probable timing of breeding opportunities for coexisting male helpers is ordered according to the dominance hierarchy established among them. Passiveness may be selectively favored in females, whose successful dispersal and pairing requires continued submissive behavior in all but territorial displays. Juvenile dominance behavior may facilitate social development through use of postures and vocalizations important to their future activities as breeding adults.