Agonistic behaviour of juvenile gulls, a neuroethological study.

The results relating to agonistic behaviour obtained during an exploration of the brain of juvenile herring and lesser black-backed gulls (Larus argentatus andfuscus) 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 number 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. While there has been an increasing interest in ever widening circles on the biological bases of agonistic behaviour, knowledge of the physiological processes underlying it are still remarkably deficient. This is true to the extent that this class of behaviour merits no more than a passing reference in current textbooks of physiological psychology (e.g. Thompson 1967; Grossman 1968; Milner 1970). Most of the information available refers almost exclusively to a small number of mammalian species (Garratini & Sigg 1969; Eleftheriou & Scott 1971; Moyer 1971). Agonistic behaviour is closely and divergently adapted to the varied socio-ecological environments of different animals and so it seems essential to explore its physiological mechanisms in a wider range of species. The agonistic behaviour of gulls· in their natural environment has been described in considerable detail and the relevant studies have contributed impressively to the factual foundations of comparative ethology (Tinbergen 1953, 1959). They have also provided much of the observational data on which current ethological theorizing about the motivational processes underlying agonistic behaviour is based (Hinde 1970). Gulls thus seemed suitable subjects for investigating the neural correlates of agonistic be·Dedicated to the memory of Erich von HoIst. 236 haviour in a non-mammalian species. The present paper reports results relevant to this behaviour obtained during a systematic exploration with electrical brain stimulation (Delius 1967, 1971a, 1971b, in preparation) of the forebrain of herring gulls (Larus argentatus) and lesser black backed gulls (L. fuscus), two closely related species of nearly identical behaviour (Goethe 1955a; Brown 1967a). Although the wildness of these animals set limits to the research, some of the results are important in that they suggest the involvement of a special neurohumoral mechanism that has been hitherto neglected in physio-ethological studies. Since immature animals were used for these experiments and their behaviour has not been described in as much detail as that of adult gulls (Goethe 1955b, 1956), a section summarizing the observations on the agonistic behaviour of normal, un stimulated birds precedes the account of the experimental results.