Agonistic behaviour of juvenile gulls, a neuroethological study

Abstract

The results relating to agonistic behaviour obtained during an exploration of the brain of juvenile herring and lesser black-backed gulls (Larus argentatus and fuscus) with electrical stimulation are reported. As an introduction the normal agonistic behaviour of immature gulls is described. While the flight and aggressive behaviour is largely unritualized the threat behaviour is more stereotyped. Three basic threat patterns are distinguished: the arched, hunched, and squat postures. The relationship of these juvenile agonistic patterns with adult courtship is considered. A large number of sites evoking fear behaviour were found, anatomically widely and incoherently distributed. It is demonstrated that the spontaneous fearfulness levels of individual subjects influences the likelihood of obtaining escape eliciting loci. Stimulation of a nubmer of these sites had an after-effect: a persistent, increased probability of escape behaviour. It seems likely that a proportion of the fear sequences elicited were secondary responses to evoked sensory hallucinations and forced small movements. None of the sites explored yielded outright attack behaviour. Thirteen sites yielded characteristic threat sequences. About half of them produced changes in ‘mood’ persisting for some 15 min. The sites were clustered in a paleostriatal-septal periventricular and an infundibular area. Histological differentiation of the neuroventricular interface at these areas is noted. Based on these it is argued that the secretion of ‘liquormones’ is responsible for the changes in ‘mood’ that followed stimulation.