This goes with the popular saying that “birds of a feather flock together”. Flocking, however, is used to refer to the behaviourial pattern exhibited when a group of birds are foraging or in flight. There are parallels with the shoaling behavior of fish, the swarming behavior of insects, and herd behavior of land animals. Flocks may be of different sizes, occur in different seasons and may even be composed of different species that can work well together in a group.
Flocking comes with a risk of increased visibility to predators, competition for food and mates and the dramatic increase in the risk of spreading diseases, nevertheless, the benefits of flocking is imperative to the survival of the flock. Some of the advantages to flocking includes:
Birds often form flocks while foraging , which allows many birds to take advantage of the same food supplies. Feeding in a group also gives more birds the opportunity to find food that one bird has already located. Foraging flocks are often comprised of mixed species that may feed on similar foods but in non-competing ways, such as chickadees that glean insects from leaves flocking with nuthatches that glean the same insects from bark.
A larger group of birds has a better chance of spotting a predator or another potential threat than a single bird has. Furthermore, a group of birds may be able to confuse or overwhelm a predator through mobbing or agile flight, and staying in a flock also presents a predator with more possible targets, which lowers the danger for any single bird.
Some bird species, most notably game birds, form mating flocks in areas called leks where males will show off their breeding plumage and courtship behavior in an attempt to attract a mate. By performing in a flock, these birds make themselves more visible to a greater number of females, increasing their chances of a successful mating.
Different types of birds form communal flocks on nesting grounds called rookeries. In a rookery, while each nest is individually tended by parent birds caring for their young, the full group of birds can take advantage of flock benefits against predators to care for their vulnerable chicks. Birds that do not use rookeries may still form family flocks, and juvenile birds from a first brood may help contribute to raising their late-season siblings.
When birds fly in flocks, they often arrange themselves in specific shapes or formations. Those formations take advantage of the changing wind patterns based on the number of birds in the flock and how each bird’s wings create different currents. This allows flying birds to use the surrounding air in the most energy efficient way.
In winter, bird flocks can share the benefit of communal warmth to survive severely cold temperatures. Many small birds will share the same tiny roost space to keep warm, often in bird roost boxes, hollow trees or other similar spaces that can help them conserve heat. Large flocks may congregate in a single tree to share their body heat as well.