"Prostitution" Behavior in a Tropical Hummingbird

Abstract

For an animal to survive, it must acquire sufficient energy to meet metabolic requirements. In many vertebrates a territory helps insure adequate energy for the resident (Brown 1964, Fisler 1969). The size and quality of the territory will depend on the spatial and temporal characteristics of the food supply and competition for the food (Holmes 1970, Wolf and Stiles 1970). Most hummingbirds feed principally on nectar although they also eat small insects (Wagner 1946, Stiles 1971, Wolf and Hainsworth 1971). Male hummingbirds of many species defend groups of flowers from other hummingbirds, from other nectar-eating birds, and sometimes from insects. The ability of a male to maintain a territory depends on the relative dispersion of flowers and his dominance relationships with other species and individuals in the area (Brown 1964, Stiles and Wolf 1970, Wolf and Hainsworth 1971). In most hummingbirds that have been studied to date, males generally dominate females; there are a few exceptions (Wolf 1969). Male dominance over females may restrict the availability of energy to the female. Thus, when food is scarce or when the optimum resources can be controlled easily by the males, the subordinate females usually must exploit poorer nectar sources than the males. Female hummingbirds of most species apparently are solely responsible for the nesting effort and there is no long-term pair-bond (Wagner 1954, Wolf 1964, Lack 1968), although males of some species may provide indirect aid (Wolf and Stiles 1970, Snow and Snow 1973). This means that even during the breeding season, females of most species are not able to cohabit or regularly to use an area defended by the male. In most species nesting females do not and probably cannot hold territories around flowers (Wolf and Wolf 1971, Stiles 1973) and they are forced to forage at energetically poor, undefended sites. Females whose behavior enables them to exploit food defended by males would seem to have a selective advantage in both the breeding and nonbreeding season. This report describes use of aspects of mating behavior in the nonbreeding season by female Purplethroated Carib Hummingbirds (Eulampis jugularis) to gain ready access to nectar supplies on male territories. Since sexual behavior in these cases is being used for an energetic benefit for the female, I term this prostitution behavior.