Response of a traplining hummingbird to changes in nectar availability

Theory predicts that nectarivores respond to changes in profitability of pa tches 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 hummingbir d, adjusts its visitation rates in response to changes in sucrose solution delivery rates. Each experiment tested the response of P. longirostris to t he following changes in the timing and volume of sucrose solution delivery: (1) increases in sucrose solution abundance at all feeders (mimicking seas onal increases in numbers of open flowers or nectar output); (2) large chan ges in sucrose solution availability at one feeder (mimicking increases or decreases of parch profitability); and (3) sudden unexpected decreases in s ucrose solution availability at one feeder (mimicking loss of nectar to com petitors). We found that P. longirostris (1) decreased visitation rates whe n the sucrose solution delivery rate was higher at all feeders, (2) increas ed visitation rates to individual feeders when their profitability increase d for whole days but did not significantly decrease visitation rates when f eeder 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.