Variability in Parrot Flock Size: Possible Functions of Communal Roosts

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Abstract
This study documents flock size in mixed-species parrot/parakeet flocks in tropical dry forest of Costa Rica. Variability in flock size was quantified on a diurnal basis, between nesting and nonnesting periods, and during departures from roost sites in the early morning. Flock size was greater when animals were congregating near the roost site near dusk than during the rest of the day or when the birds were departing the roost. Flocks were smallest in the first half of the dry season when they are reported to nest. Three hypotheses (Information Center [IC], Diurnal Activity Center [DAC], and a general foraging hypothesis) all make predictions relating the size of specific types of flocks to the density and distribution of food resources. As predicted, by the foraging hypothesis, diurnal flock size was positively related to the density of potential fruit resources, and flocks were largest when resources were uniformly distributed. However, contrary to predictions of the IC and DAC hypotheses, roosting flock size was not related to the density and distribution of food resources. The size of flocks departing roost sites in the morning was small, and evidence suggested that these flocks may have been avoiding following the flocks that left previously.