The study of the structure and function of food webs is in part a rather esoteric branch of the field of theoretical ecology. However, food web structure and function are also important topics in applied conservation biology. Although the functional role of predators in ecosystems is far from fully understood, there is little doubt that predators of various sorts play key roles in producing what we regard as normal community structure and function.

Changes in the abundance of different predators have been shown or suspected to lead to various sorts of ecological imbalances. For example, in the absence of large predators, smaller predators have been found in some cases to increase in number--a phenomenon sometimes termed "mesopredator release ." In turn, the proliferation of small and medium-sized, generalist predators is believed to have resulted in increased rates of bird nest predation, both in fragmented, suburban habitats in the U.S. (Wilcove 1985) and in tropical habitats isolated by human activities (Loiselle and Hoppes 1983). In tropical forests, there is some evidence that the disappearance of large predators from isolated forest tracts may reverberate through the community, resulting even in changes in the species composition of the tree community (Terborgh 1992, Terborgh and Wright 1994).

We consider it very likely that food web structure and function undergo dramatic changes as landscapes are subjected to progressive deforestation and habitat fragmentation. We predict that food web structure in isolated forest fragments is related to factors such as fragment size and degree of isolation (i.e., whether organisms move freely through the surrounding habitat matrix), and may differ radically from that observed in continuous forest. However, we are a long way from knowing whether this prediction will prove true; little is yet known of food webs in areas of continuous forest, and even less is known of food webs in habitat fragments.

Probably the most complete documentation of the food web of a tropical forest to date is that of Reagan and Waide (1996) for the Luquillo Experimental Forest in Puerto Rico. However, even in their detailed study, the diet of birds is reported in quite general terms, and only five species of raptorial birds occur in this much-simplified island avifauna. Even the best-studied Neotropical mainland sites--La Selva and Monteverde, Costa Rica; Barro Colorado Island, Panama; and Manu, Peru--have not been the site of thorough analyses of food webs among the vertebrates, although a long-term study of diets of predatory vertebrates is under way at La Selva (Greene 1988). A recent paper (Poulin et al. 2001) makes an interesting contribution, documenting the degree to which many primarily insectivorous, non-raptorial birds in Panamanian forest included small lizards and frogs in their diet.

For no tropical raptor community has a thorough analysis of community-wide diets been achieved. To date, the closest thing to such a study is that of Robinson (1994), in which he describes habitat use, hunting behavior, and diet of the raptors of Manu National Park, Peru. Voous (1969) provides a somewhat similar overview of raptor diets in Surinam.

At Tikal we collected dietary data for 20 raptor species, totaling more than 7,000 prey items identified at least to the level of Class. Sample sizes were as follows:

Number of Diet Items Documented for Raptor Species at Tikal

Our analyses of these data from the standpoint of the raptor community's ecology are still underway. Without a doubt, these data will provide the most detailed portrait to date of the diet of a tropical forest raptor community.

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