Feeding guilds of neotropical hummingbirds are known for their diversity and flexibility of composition, but the actual mechanisms that determine the structure of these guilds are unknown. It is known that guild member species differ in their ability to exploit different resource states and that changes in guild structure can be correlated with changes in food availability. Thus, it seems probable that differences in energetic constraints are a major mechanism behind changes in guild composition, yet this has not been empirically demonstrated. It is the goal of this study to quantify this suggested link between the energetic success of individual species and their relative representation in the guild. Syntopic pairs of species found at Monteverde, Costa Rica, will be used to test a priori predictions on relative energetics. Energy budgets will be measured using: a) flight-cage experiments to quantify energetic responses to manipulated changes in competitor pressure and food availability, and b) field metabolic rates (using doubly-labeled water) during periods of high versus low resource availability. The research will be conducted by Mr. Harry Tiebout under the direction of Dr. Peter Feinsinger. This excellent team assures a productive project on an exciting topic in tropical ecology.
