Interspecific Aggression by Yellow Warblers in a Sun Coffee Plantation

Abstract

Non-breeding habitat use is mediated infrequently by interspecific aggression in migratory birds. Such aggression occurs most commonly among birds exploiting rich resource patches such as nectar, fruit, or other similar resources (Greenberg et al. 1994). Interspecific territoriality and dominance is less commonly noted among insectivorous species (Rappole and Warner 1980, Greenberg et al. 1994). One such system of interspecific territoriality was recently reported for Yellow Warblers (Dendroica petechia) overwintering in riparian trees in cattle pastures (Greenberg and Salgado-Ortiz 1994). Greenberg and Salgado-Ortiz present data suggesting that such patches constitute rich resource islands in an otherwise inhospitable habitat. Furthermore, consistent with the hypothesis of Orians and Willson (1964), the transformation of structurally diverse forest to more open agricultural habitats and the concomitant reduction in abundance and diversity of birds should increase the defensibility of resources. Based on these considerations we hypothesize that interference competition could be important in other tropical agroecosystems where tree cover is substantially reduced. One such agroecosystem is coffee plantation. Sun coffee plantations have taken hold recently and replaced traditional shaded coffee plantations throughout much of Latin America (Perfecto et al., in press). In this note we provide some support for the hypothesis by presenting our observations of interspecific aggression by Yellow Warblers defending isolated trees in a sun coffee plantation in Guatemala.