Year: 1979
Type: article
Abstract: DUring the non-breeding season, many shorebirds defend feeding territories.Our studies in coastal California and eastern Argentina examine the extent of shorebird ' winter' territoriality, and describe its ecological context.Eleven species in California and 13 in Argentina defend territories for varying periods of up to several months' duration.The expression of territoriality differs in extent between species, individuals, and habitats, being most strongly developed in local populations foraging on the short-grass pampas and seasonal wetlands of coastal Argentina.Explanation of this variation may best be sought in terms of individual responses to local habitat conditions affecting the energetic costs and benefits of defending foraging sites.One such habitat parameter appears to be the length of time that local areas are available for foraging.Other hypotheses, such as preparing individuals for breeding behavior or decreasing predation risk, are considered and tentatively rejected.Many shorebirds defend territories in the winter.Yet their activities frequently pass unnoticed, overshadowed by the spectacular size and unison of nearby winter shorebird flocks.The striking contrast between these two spacing strategies, often juxtaposed across a defended boundary, poses a fundamental ecological and evolutionary question: Why should a bird indulge in territorial defense while others survive nonaggressively?In this paper we establish a framework for considering this question by examining the characteristics and extent of shorebird non-breeding territoriality.Our data stem from several seasons' work in two localities, including 18 months observing North and South American species overwintering in coastal Buenos Aires Province, Argentina, and three winters at Bodega Bay in central coastal California.During these studies we have concentrated on the White-rumped (Calidris fuscicollis) and Buff-breasted (Tryngites subrujicollis) sandpipers in Argentina, and the Sanderling (Calidris alba) in California, switching opportunistically to other species as circumstances permitted.In addition we draw upon many field seasons with breeding ,and migrating shorebirds along the arctic coast of Alaska.Territorial non-breeding shorebirds obtain control of resources within a defended area through aggressive spatial defense.In many cases an individual gains exclusive use of the area; in others, however, it does not exclude all intruders successfully.The defended site is usually fixed, with persistent boundaries that are defined by referents external to the aggressing bird.In both these respects territorial wintering shorebirds meet the most stringent criteria for territorial behavior (Noble 1939, Pitelka 1959, Wilson 1975).But they also deviate from its classic form.In fact, individual variability is so common in such central characteristics of winter shorebird territoriality as size of territory, duration and consistency of defense, dependence on territorial resources, etc., that the variation itself must be acknowledged as an essential feature of the spacing pattern.As will become evident below, the variation also serves as a useful tool for dissecting the possible benefits or costs of territorial behavior.Through this review, therefore, we will emphasize not only the characteristics of winter territoriality but also its patterns of variation.
Language: English
Topic: Avian ecology and behavior
Subfield: Ecology
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W1493812546