Community Organization Among Neotropical Nectar-Feeding Birds

Amer. Zool. , 18:779-795(1978). Community Organization Among Neotropical Nectar-Feeding Birds Peter Feinsinger Department of Zoology, University of Florida, Gainesville, Florida 32611 AND Robert K. Colwell Department of Zoology, University of California, Berkeley, California 94720 synopsis. Assemblages of neotropical hummingbirds are organized according to parameters of available resources and morphological-behavioral attributes of particular hummingbird species. We distinguish five types of fiowers relative to hummingbird foraging, and we define six community roles for hummingbirds in exploitation of various flower types. These roles are: high-reward trapliners, which visit but do not defend nectar-rich fiowers with long corollas; territorialists, which defend dense clumps of somewhat shorter fiowers; low- reward trapliners, which forage among a variety of dispersed or nectar-poor fiowers; territory-parasites of two types (large marauders and small filchers); and generalists, which follow shifting foraging patterns among various resources. Simple communities on islands usually contain one species of low-reward trapliner or generalist and one territorial species, and sometimes support one high-reward trapliner; often these species are sexually dimorphic. More complex mainland communities support varying numbers of species in different roles, depending on the relative importance and constancy of different flower types. High-reward trapliners are particularly important in forest under-stories, while forest canopies and open habitats support large numbers of shorter-billed, mobile birds filling the other five roles. We conclude by pointing out the many parallels that exist with other consumer groups. Our geographically diverse studies have been aided by numerous persons and organizations. In addition to those acknowledged elsewhere, we are particularly grateful to: J. A. Wolfe and L. A. Swarm, for their continuing contributions to studies on Trinidad and Tobago; S. Naeem and M. Lentrell for technical assistance; M. C. King, for expert assistance in the field and in the preparation of this paper; J. Ter- borgh, for the generous loan of unpublished data; H. A. Ford, for access to an unpublished manuscript; J. A. Brown and A. Kodric-Brown, for comments on the manuscript; A. B. Bolten, for stimulating discussions on organization among neotropical bees; and M. Bon Saint Come, for hospitality and assistance on Mar- tinique. Feinsinger's field work in summer 1975 was financed by a Venture Grant and a Faculty Research Grant from the University of Denver; his current study on Trinidad and Tobago is financed by NSF grant DEB 76-20371. Colwell's work in Chile was supported by the Ford Foundation and by NSF grant GB 31195; his work in Trinidad and Berkeley was partially financed by an NIH Biomedical Sciences grant and by the Committee on Research at the University of California. INTRODUCTION Terrestrial habitats in the American tropics commonly support several species of birds that feed primarily on nectar. Repeated patterns in the morphology and behavior of coexisting species suggest that certain basic principles are involved in the ecological organization of these as? semblages. Investigation of these princi? ples is facilitated by several factors. Nectar production and nutritional value are pre? cisely measurable. Foraging patterns of birds are easily observed and quantified. The coevolution of bill morphology and flower morphology sets certain limits on the patterns of particular species. Since behavioral interactions between birds are also obvious, it is often possible to infer the effect of interference on resource use. The considerable tactability ofthe bird-flower 779