The hawk species includes more than 250 types of birds of prey. With this wide variety of sizes and habitats, not all hawks follow the same rules. In general, however, hawks tend to be solitary birds, living with a mate during the spring but otherwise surviving alone -- except the birds that fly to warmer climates in the winter, when they create large flocks during the migration.
When hawks flock, it's called a kettle of hawks. A kettle might contain thousands of birds, depending on the type of hawk and the time of year. They don't group with the same birds every year -- at least not on purpose, although it's likely there's some overlap between seasons with such large kettles. Typically preferring to live alone, hawks that migrate take advantage of large groups to help find warm wind currents known as thermals. The kettle spirals upward, allowing the warm air to help them soar higher. When the thermal ends in a mass of cold air, the hawks glide in the direction of their migration. Allowing warm air to give them lift so they can glide lets them conserve the energy they would expend if they were continuously flapping their wings. This gives them the endurance to make it thousands of miles to their destinations.
When They Flock
Many species of hawk -- including the broad-winged hawk, sharp-shinned hawk, American kestrel and northern harrier -- form kettles twice a year. They leave American soil in the fall, embarking on journeys sometimes thousands of miles long; some travel as far as South America. In spring, often April or May, the hawks return to their breeding grounds. Many seek the same nests they used the previous year, although some hawks build new nests each year.
The Rest of the Year
Migrations can take more than a month, depending on how far the birds need to go. When they're not flying north or south, it's rare for hawks to congregate in flocks. During breeding season in the spring, a male and female hawk might live together while mating and raising their young. After the babies leave the nest, the couples often separate to live solitary lives until the next winter migration. Many mate with the same bird every year, unless the other bird dies. In that case, the surviving bird takes a new mate. When the birds reach their winter destinations, they live alone rather than remaining in the kettle until it's time to fly north again to breed.
Hawks That Don't Flock
Because hawks only flock when they migrate, hawks that don't migrate also don't flock. The red-shouldered hawk, for example, tends to stay in the same area all year. Some who live in the northern areas of the country might fly to the southern states or just inside Mexico, but because the distance isn't as great as some hawks fly, they don't travel in kettles. Some hawks, such as Harris's hawk, live in small groups of three or four, although it's not considered a flock. These birds hunt together and often nest together, but they live mostly in warm climates, such as desert areas, so there's no need to migrate.
- Raptor Trust: Hawk Facts
- Mass Audubon: Hawk Migrations in Massachusetts
- North Jersey: The Great Migration Above Montclair: Hawk Watchers Flock to Site to Count Birds of Prey, Observe Southbound Flight
- Cornell Lab of Ornithology: Frequently Asked Questions
- Arizona-Sonora Desert Museum: Hawks and Eagles
- BioKids: Red-shouldered Hawk