Response of a traplining hummingbird to changes in nectar availability

Theory predicts that nectarivores respond to changes in profitabilityof patches of flowers or feeders by adjusting visitation rateto increase reward size. We conducted a set of experiments inan outdoor enclosure with seven feeders to determine how Phaethornislongirostris, a traplining hummingbird, adjusts its visitationrates in response to changes in sucrose solution delivery rates.Each experiment tested the response of P. longirostris to thefollowing changes in the timing and volume of sucrose solutiondelivery: (1) increases in sucrose solution abundance at allfeeders (mimicking seasonal increases in numbers of open flowersor nectar output); (2) large changes in sucrose solution availabilityat one feeder (mimicking increases or decreases of patch profitability);and (3) sudden unexpected decreases in sucrose solution availabilityat one feeder (mimicking loss of nectar to competitors). Wefound that P. longirostris (1) decreased visitation rates whenthe sucrose solution delivery rate was higher at all feeders,(2) increased visitation rates to individual feeders when their profitabilityincreased for whole days but did not significantly decrease visitationrates when feeder output decreased; and (3) responded to sudden foodlosses at a feeder (due to simulated competition) by increasinguse of that feeder for 1 or 2 h after the loss.