A kettle is a collective term for a group of migrating raptors or, in general, a flock of birds of prey. While most often applied only to hawks or falcons, the term kettle can be used to describe any types of raptors when they are seen in a large group. It is generally only used to describe birds in flight, however, and groups of raptors on the ground are referred to by other terms.
The term kettle is believed to have originated from descriptions of hawk flocks looking like liquid or 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.
Why Raptors Kettle
Most birds of prey are generally solitary, defending and hunting on their individual territories and only occasionally seen together, such as when several vultures may feed on a single carcass. There is one time, however, when dozens, hundreds, or even thousands of raptors will seem to flock together, and that is during migration.
Many birds of prey follow the same route during migration to take advantage of the best thermals and other wind currents to aid flight. Thousands of raptors may be seen in the same flight pattern when those air currents are at their best, even flying within just a few feet of one another on favorable updrafts. This creates the appearance of a coordinated flock as many raptors wheel and soar together, especially in areas such as mountain passes where airspace is limited and the birds draw even closer to one another.
This group activity is an illusion, however. While the birds seem to be flocking together, their goals and behavior are still individual and they are not actually cooperating in any way other than to share airspace and not behave aggressively toward one another. All other aspects of this behavior, such as the timing of the flight, the 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.
Bird Kettle Species
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 will vary depending on bird ranges, prey availability, recent weather, local geography, and other factors. Surprise guests are also common in large mixed kettles, and there is always the possibility of an unusual sighting within an otherwise relatively uniform kettle.
While application of the term kettle will vary and is a matter of personal preference, it is generally reserved for groups larger than a dozen birds of prey.
Where to See Bird Kettles
Witnessing a kettle of hawks or other raptors can be an amazing experience for any birder, and with the right planning, every birder can have the opportunity to see a kettle of their very own.
The key is to locate a suitable hawkwatch site, a location where kettles of such magnitude have been recorded that annual counts of migrating raptors are organized. These counts assist ornithologists and wildlife officials with judging the health of raptor populations, seasonal breeding successes, and other research.
There are hundreds of these locations worldwide, but the most popular and most productive hawkwatch sites include specific geographic features, such as:
- 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 to learn not only the best sites but also the best times to see raptors in great numbers. In many areas, kettling behavior may last for several weeks during migration, but there are definite peak periods when the birds are more numerous and viewing is more popular.
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.