Notes On the Behavior of Some North American Gulls. Ii: Non-Aerial Hostile Behavior of Adults
Most of this paper is a description and analysis of the hostile behavior patterns of adult Ring-billed Gulls and Franklin's Gulls on the ground or water. Both species have elaborate repertories of these patterns, including a variety of unritualized reactions and an even larger number of ritualized displays. The causation of these patterns is analyzed in terms of their motivation. All of them appear to be produced by simultaneous activation of the attack and escape drives; each pattern being produced by its own particular combination, i.e. relative and actual strength, of these drives, (with the addition of other drives, such as sex, in some cases). An attempt is also made to trace the derivation and social signal function(s) of the display patterns. A few of the corresponding patterns of the California Gull and Bonaparte's Gull are described very briefly. The comparative, evolutionary, implications of some of the displays are discussed at greater length, as they seem to be particularly suggestive, (more so than most of the aerial hostile patterns). The non-aerial hostile repertory of adult Ring-bills is very reminiscent of the other "typical Larus" gulls; but it does include a few peculiar features which have not been found in either the Herring Gull or the Common Gull. The California Gull is also very similar; and some of its displays are almost exactly intermediate in form between the homologous displays of the Herring Gull and the Ring-bill. The adult non-aerial hostile displays of Franklin's Gull are more distinctive. They are most reminiscent of the Laughing Gull; but the repertories of the two species are strikingly different in several important features. The repertories of the Ring-bill and Franklin's Gull are rather more similar than would be expected in view of the great morphological and ecological differences between the two species. This might suggest that the displays they hold in common are primitive in the family Laridae, (and the arrangement of these displays may also be primitive). It is possible, in fact, to make a tentative and hypothetical reconstruction of the probable complete hostile repertory, both aerial and non-aerial, of the ancestral gull, based upon comparison of the adults of all species whose behavior has been described in this and other publications.