Solo Flight vs Flocks

January 24, 2024

Question: Why do some species of birds fly in groups of hundreds – or thousands – while some fly or live seemingly single?

Answer: There can be many benefits to living or traveling in groups. Flocks of birds may gather for longer-distance migration or even shorter-distance local movements. Groups of birds also may assemble during the breeding season with many individual birds nesting in a colony. The main advantages of being an individual bird in a flock or nesting colony have to do with safety and finding food resources. Birds within a flock can help alert others to potential predators and other threats. The more eyes there are, the better it is to detect predators. Being in a group can also decrease the chance of any one individual within the flock or colony being taken by a predator. The scientific name for this is called the dilution effect, the more bodies there are the lower the chances of being the individual taken by the predator. Birds in a flock also can improve food-finding and wayfinding for other members within the group. For example, snow geese are a migratory bird that breed in the arctic and overwinter in parts of California and elsewhere in the U.S. and Mexico. The juvenile snow geese hatched that season in the arctic breeding colony have never migrated south. It’s common for juveniles to migrate in family groups with their parents and siblings within the larger flock, which helps juveniles find their way and locate food resources. For bird species that feed on relatively abundant plants or insects, such as waterfowl or small songbirds, it can be beneficial to be in the company of others both for safety and locating food resources.

The primary disadvantage to group living is competition for food and other resources like mates or territory. When a bird must expend a lot of energy to obtain its next meal, such as catching live prey, it can be beneficial to forage alone. For example, many raptors are mostly solitary outside of the breeding season. An individual raptor is in direct competition with its neighbor for limited food resources. Catching live prey, such as small mammals and birds, can require high energy expenditure to obtain. Given the high cost of catching the prey, the raptor benefits most from consuming the prey itself without having to share.