Structure and Dynamics of Interspecific Flocks in a Neotropical Mid-Elevation Forest

ABsTP,CT.--Mixed-speciesflocks of marked individuals were studied for 3 yr in a middleelevation neotropical forest.Most flock participants maintain pair bonds and defend territories throughout the year.Residents only follow flocks that are in their territories, so intraspecific group size of flocks is limited primarily to pairs and pairs with young.When a flock leaves the territory of one of its members, the member generally drops from the flock, and the neighboring conspecific, whose territory has just been entered, may join.The propensity for birds to join varies with season, time of day, climate, species composition of the flock, and proximity of the passing flock.A three-to four-fold annual cycle in interspecific flock participation is primarily a consequence of more frequent and consistent flocking by year-round residents.Larger mixed-species flocks are not the result of shifts in population structure or densities.Nonresidents from local sources and North American migrants play minor roles in increased flock size.Mixed flocks are structured groupings whose membership is limited to a few resident individuals of relatively few species.A given flock at any time of the year will consist of some subset of those individuals, with identity of the subsets depending on the flock's location.