How the mountain chickadee procures more food in less time for its nestlings

Abstract

Parent mountain chickadees (Parus gambeli) visit the same foraging location on consecutive flights more frequently than expected by chance. This pattern of repetitive return to a foraging location does not increase the frequency of capturing the same prey on consecutive flights. The quantity of prey captured on a visit also does not change significantly with repeated visits to a foraging location. Foraging time, however, is significantly shorter during repeated visits to a foraging location. Foraging time is therefore a major determinant of whether a run of consecutive flights to a location occurs. Decreased foraging time is also a benefit of selecting the same prey type on consecutive flights. Over the course of a day, the prey types returned on the greatest percentage of flights are returned multiply per flight. These prey are usually small and are probably present at high densities in the environment. Large prey size is the second best predictor of frequency of a prey type in the diet. Short foraging time to capture a prey is the third best predictor. Thus prey which can be readily obtained in large numbers, even if they are small prey, are preferentially returned to older nestlings. The mountain chickadee uses information on foraging time to decide when to move to a new foraging location or when to pursue a different type of prey. These decisions should increase the amount of time available for prey gathering.