Flocking has many benefits for birds.

Steve Jurvetson

Why do birds of a feather flock together? Understanding why birds flock can help birders understand bird behavior and the fight for survival all their feathered friends face.

About Bird Flocks

Many bird species are gregarious and form flocks for different reasons. Flocks may be different sizes, occur in different seasons and may even be composed of different species that can work well together in a group. Flocks are so prevalent in some bird species that these groups of birds have special names, such as a raft of ducks, a charm of finches, a horde of ravens or any other of the names for flocks of birds. But no matter what a flock is called, it always has a benefit for the birds that make it up.

Advantages of Bird Flocks

Birds do not engage in any behavior that does not bring them a benefit for survival in some way. There are many advantages to flocking, including:

• Foraging: 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.





• Protection: 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.





• Mating: 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.





• Raising Families: 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.





• Aerodynamics: 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.





• Warmth: 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.

Disadvantages of Bird Flocks

While there are many advantages to flocking behavior, birds also take a risk when they assemble in flocks. The problems with flocks include:

• Visibility: The more birds there are in a flock, the more noise and motion it makes, and the more visible it can be to predators. Predators may stalk flocks searching for the weakest members, and several predators can be attracted to the same flock, causing a constant threat to the birds.





• Competition: Larger flocks need greater amounts of food and have more competition for mates, making it more difficult for each bird in the flock to find enough food or a suitable mate. Weaker, slower members of the flock may suffer if supplies are limited and they cannot compete as ably to get the resources they need to survive.





• Disease: When many birds congregate closely together, the risk of spreading diseases increases dramatically. Many avian diseases are spread through either direct contact or fecal matter, and a larger flock has more potential for a disease to ravage an entire local population of a particular bird species. This can often be seen in backyard flocks with house finch eye disease or avian pox.

Despite the risks, the advantages of flocking are great enough that many different types of birds assemble in small, medium and large groups for different reasons. From a roaming band of foraging finches to a stupendous migrating flock of geese, flocks of birds can be an amazing sight for birders to enjoy, even more so when they understand how important those flocks can be for birds' survival.

Photo – Flock of Gulls © Steve Jurvetson