Response of a traplining hummingbird to changes in nectar availability

Abstract

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