Group(s) of birds usually called flock. Two basic factors cause birds to aggregate: 1) congregation into groups due to social behaviour (flocks), 2) groupings as a result of ecological factors alone (food, shelter etc). Flocks may consist of a single species (monospecific) but also mixed aggregations occur. In the latter case these usually are species with a different feeding habit (mixed foraging party). See also 'flock(s)'.

Alternative form for aggregation : aggregations.