Effects of feeding height and distance from protective cover on the foraging behavior of wintering birds

Foraging behavior that balances feeding efficiency with predation risk avoidance may be selected for; thus, foraging animals may choose among sites and achieve various giving-up densities under different feeding conditions. We compared the frequency and duration of visits and the feeding efficiency of a mixed-species wintering bird flock among feeders set up at three heights within woods, at the edge between woods and dense shrub, and in open fields to investigate the feeding height preference of birds and its relationship to the extent of openness of the sites. Carolina chickadees (Parus carolinensis Audubon, 1834) and tufted titmice (Parus bicolor L., 1766) accounted for 96% of the total number of visits to feeders and 95.9% of the total time spent on feeders. Birds tended to visit higher feeders and feeders in the woods and at edge sites more frequently than they visited lower feeders and feeders in open fields. Birds also spent more time on higher feeders and feeders in the woods and at edge sites than on lower feeders and feeders in open fields. However, the feeding height preference changed over the course of observations, and different patterns were observed at different sites. In the woods and at the edge, bird visits shifted to the lower feeders earlier; in contrast, birds preferred higher feeders throughout the period of observation in open fields. Feeding efficiency was lower at open sites than in woods and at edge sites, but birds spent the least time per seed on low feeders at open sites. Seeds on higher feeders and in woods or at edge sites were removed faster. Regardless of the height and locality of feeders, birds preferred energy-rich oil-type seeds over energy-poor striped seeds.