FEMALE AGGRESSION IN THE EUROPEAN STARLING DURING THE BREEDING-SEASON

Intraspecific female aggression during the breeding season can have se veral different functions: defence of resources, defence against intra specific brood parasitism and defence of mating status. The intraspeci fic aggressive behaviour of breeding female starlings, Sturnus vulgari s, was examined by exposing them to a simulated intrusion of a conspec ific bird. A caged male or female starling was placed close to the nes t of a breeding pair. Aggressiveness was scored as the proportion of t ime birds spent near the caged birds after discovery. Caged females el icited stronger responses from females than caged males. Females sang at caged females and sometimes also attacked them. They were most aggr essive towards them during the pre-laying period and less so during th e egg-laying, incubation and nestling periods. Females were more aggre ssive towards a caged female when their mate had access to an addition al nestbox to which he could attract an additional female, then when h e had not. A time-budget study demonstrated that females spent more ti me near their nest site during the pre-laying period when their mate h ad access to an additional nestbox than when he had not. These pattern s are most consistent with females trying to secure male brood-rearing assistance by preventing or delaying the settlement of secondary fema les, since early established secondary females may compete for male he lp in incubating eggs and feeding nestlings. (C) 1997 The Association for the Study of Animal Behaviour.