is a group of birds
behavior in flight, or while foraging. The term is akin to the herd
. The benefits of aggregating in flocks are varied and flocks will form explicitly for specific purposes. Flocking also has costs, particularly to socially subordinate birds, which are bullied by more dominant birds; birds may also sacrifice feeding efficiency in a flock in order to gain other benefits. The principal benefits are safety in numbers and increased foraging efficiency. Defense against predators is particularly important in closed habitats such as forests
where predation is often by ambush
and early warning provided by multiple eyes is important, this has led to the development of many mixed-species feeding flocks
. These multi-species flocks are usually composed of small numbers of many species, increasing the benefits of numbers but reducing potential competition for resources.
Group size is a major aspect of the social environment of gregarious animals.
In Denmark, there is a biannual phenomenon known as Black Sun (Danish: Sort Sol), when flocks of European Starlings gather in vast numbers, creating complex shapes against the sky.