Introduction

In many species, an individual that finds itself in a losing position may interrupt a contest to harass a bystander (i.e. an apparently uninvolved third party) aggressively or may do so immediately after hostilities with the original opponent have ceased. Such ‘redirection’ of aggression (Bastock et al., 1953) is often interspecific; for example, rollers and chasseur-type kingfishers (Coraciiformes) are reported to dash away frequently during disputes to attack small passerines, doves and plovers (Moynihan, 1998). The scapegoats are typically not ecological competitors but do tend to be smaller and inoffensive individuals, both literally and figuratively, and thus relatively safe targets. In socially living taxa, however, redirection is most commonly directed towards a lower-ranking group member (where available) and, therefore, is usually intraspecific. Both aspects of redirection are conveyed by the description of tensions between spotted hyaenas Crocuta crocuta at a kill, producing a cascade of aggression, in which ‘A chases B, B chases C, C chases D, and D chases vultures’ (Zabel et al., 1992, p. 129).

Redirection of aggression has traditionally been explained as a means of reducing the physiological arousal associated with participation in a conflict. The neuroendocrine responses underlying the preparation for ‘fight or flight’, whilst essential in the immediate context, can be detrimental if they remain activated over prolonged periods. Chronically elevated secretion of glucocorticoids, for example, is associated with a range of cardiovascular pathology, depressed immune function and compromised digestion, growth and reproduction (reviewed by Sapolsky, 1998).