Why Raptors Kettle: Flocking Birds of Prey

Flock of Birds of Prey

Kettle of Migrating Hawks
bgv23/Flickr/CC by 2.0

Raptor and kettle: two words you've heard before but mean something different than the commonly known definitions when it comes to birds. A raptor is a bird of prey, i.e., one that feeds on vertebrates. (These are not the birds you see in your backyard pecking at insects and feeding worms to their young!) A kettle is a collective term for a group of migrating raptors or, in general, a flock of birds of prey.

What Is Kettling?

Kettling is when a group of birds of prey migrate as a group. They are not flying as a group purposely to travel together, they just happen to all be taking advantage of the same optimal migration conditions.

While most often applied only to hawks or falcons, the term kettle can be used to describe any types of raptors seen in a large group. It's generally only used when referring to birds in flight; groups of raptors on the ground are characterized by other terms.

Why Raptors Kettle

Most birds of prey are generally solitary, defending and hunting on their individual territories. They are only occasionally seen together, such as when several vultures feed on a single carcass. There is one time, however, when dozens, hundreds, or even thousands of raptors will seem to flock together: during migration.

Many birds of prey follow the same route during migration to take advantage of the best warm winds (thermals) and other wind currents to help with flying. Thousands of raptors may be seen in the same flight pattern when those air currents are at their best, flying just a few feet of one another on strong updrafts. This creates the appearance of a united flock as many raptors soar together, especially in areas where airspace is limited and the birds fly even closer to one another.

However, this is just an illusion. While the birds seem to be flocking together, their goals and behavior are still individual—they are not actually cooperating in any way other than to share airspace. All other aspects of this behavior, such as the timing of the flight, direction, location, and even the altitude, are based on the best possible flight dynamics for each individual bird to save energy, conserve strength, and fly more efficiently.

Fun Fact

The term kettle is believed to have originated from descriptions of hawk flocks looking like soup boiling in a cauldron, pot, or kettle due to the bowl-like shape of thermal currents the birds use for soaring. The birds' pattern of flight is also similar to the steam rising from a teakettle.

Birds That Kettle

A kettle of raptors may be just one species of bird, or these flocks may include several types of raptors. Mixed flocks are particularly common during peak migration periods or in areas where flight paths are restricted, such as through gorges or along cliff coastlines. Raptors commonly seen in kettles include:

  • Accipiters: Cooper's hawks, sharp-shinned hawks, and sparrowhawks
  • Buteos: Broad-winged hawks, red-shouldered hawks, and Swainson's hawks
  • Eagles: Bald eagles, golden eagles, steppe eagles, and other eagle species
  • Falcons: Peregrine falcons, kestrels, hobbies, and merlins
  • Kites: Swallow-tailed kites, red kites, and black kites
  • Vultures: Turkey vultures, black vultures, and Egyptian vultures

These are just a few raptors that may regularly appear in kettles. The exact species composition of a large kettle varies depending on bird ranges, prey availability, weather, geography, and other factors. Surprise guests are also common in large mixed kettles, and there is always the possibility of an unusual sighting in the mix.

While use of the term kettle will vary, it is generally reserved for groups larger than a dozen birds of prey.

Where to See Bird Kettles

The key to seeing a kettle is to locate a good hawkwatch site, a location where large enough kettles have been recorded that there are annual counts of migrating raptors. These counts help ornithologists and wildlife officials know the health of raptor populations, seasonal breeding successes, and more.

There are hundreds of these locations worldwide, but the best hawkwatch sites share a few common features:

  • Narrow areas where air currents are stronger and birds are forced into smaller areas for more spectacular kettles, such as in mountain passes or between two large bodies of water
  • Shorelines where the birds may gather before attempting to cross a large body of water, such as along coasts between continents or adjacent to large lakes
  • Steep gorge-like or canyon areas where rivers create passes between mountains and air currents are favorable along the gorge or canyon
  • Ideal viewing locations, such as overlooks, watchtowers, or other accessible spots where watchers can set up a base, whether platforms are natural or constructed

Birders interested in seeing a kettle should contact local hawkwatch groups and birding organizations. They can tell you the best sites and times to see raptors kettle. In many areas, kettling behavior may last for several weeks during migration, but there are definite peak periods when there are more birds.

Tip

Volunteers are often welcome to participate in organized hawkwatch counts, and birders should brush up on how to identify raptors, how to identify birds in flight, and how to count birds so they are up to the challenge.