Copying of Foraging Locations in Mixed-Species Flocks of Temperate-Deciduous Woodland Birds: An Experimental Study

Abstract

We examined copying of foraging locations among the members of mixedspecies foraging flocks of deciduous woodland birds. We used 10 captive flocks, each consisting of a male and a female Downy Woodpecker (Picoides pubescens), a male and a female White-breasted Nuthatch (Sitta carolinensis), three Tufted Titmice (Parus bicolor), and two Carolina Chickadees (P. carolinensis). Low-ranking individuals were less likely than dominants to take even a single mealworm (Tenebrio sp.) from a cryptic food supply, but when they did take at least one mealworm they tended to do so more quickly than dominants. Subordinates were quicker to follow a conspecific than a dominant heterospecific in extracting a mealworm from the cryptic supply. We examined how two types of learning, local enhancement and social facilitation, might enhance food finding among these four species. Compared to higher-ranking individuals, subordinates were more likely to generalize to a similar foraging site (social facilitation) than to go to the exact site of a food find (local enhancement). Our results also suggest that the intraspecifically subordinate chickadees and titmice may be at an advantage in mixed-species rather than single-species flocks because dominant heterospecifics may interfere with their foraging less than may dominant conspecifics.