Notes On the Behavior of Some North American Gulls. Iv. the Ontogeny of Hostile Behavior and Display Patterns

Abstract

This paper is primarily a description of the development of ritualized display patterns (specialized social signals) in young Franklin's Gulls (Larus pipixcan) and Ring-billed Gulls (L. delawarensis) during the period from hatching to fledging. All the display notes and calls of older birds seem to be derived from the Distress Notes of newly-hatched chicks. These original Distress Notes (which may be divided into high intensity and low intensity types) occur whenever a chick is uncomfortable or frustrated in any way. They are designed to make the parent remedy the situation which is causing the discomfort. The subsequent development of the original Distress Notes is essentially a process of elaboration and simultaneous segregation or restriction. The two original types become more distinct morphologically; one of them breaks up into several new types; and each type becomes less and less generalized, eventually becoming fixed or confined to a particular, single, frustrating conflict or ambivalent situation, in which two or more drives (attack, escape, and sometimes some other) are activated simultaneously. These calls and notes also acquire a hostile signal function, becoming threat or appeasement. Most of the display postures and movements develop by a process of what may be termed ontogenetic ritualization. They first appear as flexible and variable patterns, without a signal function, and gradually become standardized (and sometimes exaggerated) as their signal function develops. They all become hostile signals; and most of them become closely associated with particular calls. These processes result in the formation of many different displays. Both young Franklin's Gulls and young Ring-billed Gulls have acquired complex repertories of hostile displays by the time they first begin to fly. The repertories of the young juvenile birds of the two species are very similar; but neither is identical with the corresponding behavior of adults. It has not been possible to trace the complete development of the adult displays (as hostile behavior declines after fledging) ; but some of the adult patterns are more or less similar to particular juvenile displays, and it may be assumed that they are derived from the juvenile patterns they most closely resemble.