Traplining foraging behavior in a tropical hummingbird species phaethornis superciliosus

Traplining nectarivores are those that visit widely dispersed and often nectarrich flowers that cannot be directly defended and are thought to follow similar routes on different foraging bouts. Phaethornis superciliosus is a large (6 g) hummingbird found in the lowland tropical forests of Central and South America, and is considered a preeminent example of a traplining hummingbird. Though P. superciliosus is considered a trapliner, no detailed studies of its movements have confirmed this. Through field observations and enclosure experiments on P. superciliosus, I examined whether they followed similar routes on different foraging bouts, and considered some factors which could affect their visitation rates to patches of flowers. In the field, birds' arrival and departure angles to/from a patch were quite similar over one to several days, and different birds used different arrival and departure directions from the same patch. This supports the idea that they were following routes, and that these routes were based on the locations of patches of flowers, rather than on open flyways through the forest. Both my field and enclosure studies suggest that P. superciliosus can detect and respond to changes in nectar production rates at individual patches along their traplines. Birds in the enclosure increased or decreased relative use of feeders when I manipulated their nectar production rates. Because traplining birds do not defend their flowers from competitors, they should respond to competition by returning sooner to flowers visited by other nectarivores (exploitative defense). In my field study, I observed a positive relationship between how long a bird waited between visits to a patch and the number of competitive visits by other birds to the patch. There was a positive relationship between the amount of nectar removed from the feeder and birds' relative use of the feeder, indicating that birds do respond to competition. The currently accepted model of constant net energy intake by territorial hummingbirds does not accurately reflect feeding behavior of traplining birds. P. superciliosus has a gross nectar intake that decreases through the day, mirroring nectar production rates in its food-flowers. I present a simulation model in which trapliners have decreasing rather than constant net energy intake rates. Model birds with decreasing net intake rates can meet their energetic needs with fewer flowers than model birds with constant net intake.Science, Faculty ofZoology, Department ofGraduat