Birds often fly in tight formations with little space between them. There are several reasons why birds might fly closely together in groups:
Aerodynamics
One major reason is aerodynamics. When birds fly closely together, they can take advantage of the uplift from the birds in front of them. The airflow over a bird’s wings gets disrupted and forms small circular currents called vortices. The vortices create an area of lift behind the bird. When flying in a V formation, the birds behind the leader can take advantage of these vortices, reducing their effort to stay aloft. The birds end up expending less energy compared to if they were flying alone.
Drafting
This energy saving effect is often called drafting. The birds flying behind are literally “drafting” off the birds in front, like race cars drafting off the car ahead on a track. Studies have estimated that birds flying in a V formation may achieve a flight range increase of up to 71% compared to solo flight. That’s a huge boost that allows migrating birds to fly much farther on the same amount of fuel.
Efficiency
The V formation positions each bird where it can maximize the lift from the bird in front. The lead bird works the hardest and tires more quickly. When that happens, the lead bird will drop back into one of the trailing positions, allowing another bird to take the lead. This frequent rotation of leadership within the formation allows the flock to maintain the energy saving benefits of the V formation over long flights.
Communication
Flying close together also aids communication and coordination within a flock. The birds can see each other well for visual signaling. Being near each other allows them to hear calls and other auditory signals. Good communication helps the flock stick together and make decisions as a cohesive unit.
Avoiding Predators
Staying close allows birds to better watch for predators. With multiple sets of eyes on the lookout, it’s less likely a predator can surprise the flock. There is safety in numbers, so a tight formation can confuse or deter predators. The flock can also mount a coordinated defense, mobbing a predator or fleeing in synchronized patterns like wave formations.
Finding Food
Information sharing helps flock members locate food sources. If one bird spots a good source of food, the others can quickly join in to take advantage. Moving as a unit, they can better claim and hold productive foraging areas.
Social and Mating Behaviors
Forming flocks provides benefits beyond aerodynamics and coordination. Flying together serves social purposes and aids in mating.
Facilitating Pair Bonds
Some bird species form monogamous pair bonds that may last for life. Flying in proximity helps maintain the pair bond between mated birds. The close presence of their mate stimulates hormonal and social responses that strengthen the attachment.
Bird Species | Mating Habits |
---|---|
Geese | Long-term monogamous pairs |
Swans | Long-term monogamous pairs |
Albatrosses | Long-term monogamous pairs |
As seen in the table above, geese, swans, and albatrosses are examples of birds that form monogamous bonds and fly together with their mates during migration and day-to-day activities.
Facilitating Courtship
Flying together also helps facilitate courtship between birds. Courtship flights allow potential mates to show off their flying skills, stamina, and coordination. This “dancing in the sky” on the wing helps pairs evaluate compatibility and solidify pairing up for breeding season.
Navigation and Guidance
There are additional benefits to birds flying closely together when migrating or traveling to new areas.
Aiding Navigation
Birds may not be familiar with the best routes and stopping points. Having more experienced flock members that know the way can guide the group. The older birds essentially act as guides. Even if just one flock member knows the route, keeping close allows the naive birds to follow along.
Providing Safety in Numbers
There is safety in numbers when moving through unknown territory or bad weather. Sticking together allows the flock to pool their senses and not lose stragglers. It also helps vulnerable migrating flocks avoid predation in unfamiliar areas.
Young Birds Learning to Fly
For young birds just learning to fly, there are additional reasons to stick close to others.
Maintaining Proximity to Parents
Juvenile birds need to stay near their parents for protection and guidance. Young birds don’t have the strength, stamina, or flying skill to keep up on their own. Flying close allows them to keep pace and not get left behind or lost.
Practicing Flying Skills
By flying with experienced flock members, juveniles can observe techniques and practice aerodynamic interactions. They learn proper timing, positioning, and coordination. The close presence of other birds provides a “safety net” as the young birds build confidence.
Disadvantages of Close Formation Flight
While flying closely in flocks provides many benefits, there are also some disadvantages and risks birds must contend with.
Increased Disease Transmission
The proximity required for formation flight allows easier spread of parasites and disease between flock members. Bacteria, viruses, and external parasites like feather lice can quickly spread through an entire flock.
Higher Competition Between Flock Mates
Resources may be more limited for large flocks, especially when food is scarce. There will be increased competition with other birds, even from within the same flock. Having to compete against their own flock mates for habitat and food can disadvantage some birds.
Greater Predation Risk
While flocks are safer from surprise attacks, dense concentrations of birds can also be a target for predators. Predators can herd flocks into dangerous areas or overwhelm them with an ambush attack. Birds packed together have less room to maneuver to escape.
Conclusion
Birds regularly fly in close formation when traveling, foraging, or migrating in a flock. Formation flight provides aerodynamic benefits that increase flight efficiency and endurance. Coordinating with flock mates aids navigation, foraging, and predator detection. Close proximity helps maintain social bonds, facilitates courtship, and enables juvenile birds to improve their flying skills. However, the close quarters also increases spread of disease and parasites between flock members. There are also risks from increased competition over resources and exposure to predation. But the overall benefits of flying closely together likely outweigh the costs for most bird species, given how commonly tight formations are observed in nature.