A
flock is a group of
birds conducting
flocking behavior in flight, or while foraging. The term is akin to the
herd amongst
mammals. 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 also increasing potential competition for resources.