Effects of Avian Foraging and Post-Foraging Behavior on Seed Dispersal Patterns of Ashe Juniper

Abstract

The effects of avian foraging and post-foraging behavior on seed dispersal patterns of Ashe juniper (Juniperus ashei) were examined. We predicted that 1) flocking species would be more efficient at dispersing seeds than non-flocking species, and 2) among flocking species, flock attributes such as size, structure, and post-foraging behavior would determine efficiency of seed dispersal by each species. We were unable to evaluate single forager species because of low sample sizes. Among flocking species foraging behavior of birds (time spent feeding, number of fruit taken per visit, number of visits, and flock size and cohesion) determined the quantity of the seed crop removed by each species. Post-foraging behavior (departure direction from feeding trees, perch type selected, and distance moved from feeding trees) determined the probability that seeds dispersed by a dispersal agent will land in a safe site for germination. Two of 15 species of avian frugivores that fed on Ashe juniper, the American robin (Turdus migratorius) and cedar waxwing (Bombycilla cedrorum), were the most important dispersers. Differences in foraging and post-foraging behavior between American robins and cedar waxwings yielded two distinct seed dispersal patterns, clumped (high density) by waxwings and scattered (low density) by robins.