Do birds of a feather flock together?
Birds of different species occasionally mix in the same flock. This is a very widespread phenomenon observed among a large variety of species in different biomes all over the world. It is commonly suggested that participants in mixed-species flocks benefit from enhanced foraging efficiency and/or increased anti-predator defense. In order to understand the mechanism of flock formation, I manipulated the availability of food and predator pressure affecting six species of wild, mix-flocking forest birds in two temperate forest sites in the Northeastern US ( New York State ). The frequency of formation and composition of mixed species flocks where measured under different experimental treatments combining changes in perceived predation pressure, abundance of food, and distribution of food. First, I show that these flocks are indeed aggregations of individuals – not merely chance encounters of randomly distributed birds. Second, I examine the changes in flock formation under different treat
