Sex roles during conspecific territorial defence in the Zenaida dove, Zenaida aurita

Abstract

Social monogamy in vertebrates often involves the joint defence of an all-purpose territory by pair members. Although both sexes presumably benefit from holding a territory, sex-related variation is often observed in territory defence at the interspecific level, particularly in birds. Most studies of territorial defence in monogamous birds, however, have been conducted on songbirds or on bird species living in temperate areas. In contrast, data on nonoscine tropical bird species remain scarce. We experimentally studied territorial defence in 20 pairs of Zenaida doves, a tropical and territorial monogamous bird species that maintains year-round pair bonds. Overall, males responded to intrusions more frequently than females. However, sex of the intruder had no effect on the reactivity of male or female residents. The use of aggressive behaviours of various intensities did not differ between males and females, irrespective of the sex of intruder. Although the percentage of male responses was correlated significantly and negatively with that of the females, the observed percentage of joint defence was significantly lower than would have been expected if pair members were reacting independently of each other. Finally, variation in reactivity of females to intruders was positively related to variation in intrusion pressure between trials, whereas no such trend was observed in males. We discuss our results in relation to the mating system of Zenaida doves and previous studies of territorial defence in birds.