The optimal foraging behavior of the Ruby-throated Hummingbird, Archilochus colubris.

Abstract

Ruby-throated Hummingbirds, Archilochus colubris, were manipulated to choose between high and low sugar concentration solutions. This was done to determine whether hummingbird behaves in accordance with the optimal foraging behavior. We set up two identical perched feeders with different sugar concentration solutions, 25% and 15%, to determine the preferred concentration. Finding that the birds preferred the higher concentration, we removed its perches thereby increasing the energy constraint by forcing the bird to hover while feeding. In both experiments, the hummingbirds visited the high-concentration feeder significantly more often than the low-concentration feeder. The removal of the perches, resulted in a significant drop in the average visit length at the high-concentration feeder, presumably because the bird was forced to expend more energy at the feeder in order to obtain food. The average visit length at the low-concentration feeder was thus significantly larger than at the high-concentration. These results suggest that the hummingbird is choosing the optimal foraging strategies because it is obtaining the greatest possible caloric gain in each case.