Captured in Marana AZ this morning 8/19/12. I watched them for a long time, hoping that they would come closer. They were at quite a distance, but still quite a sight for me. As far as I could tell from the distance these were all Swainson’s Hawks. There were about 50-75 hawks in this kettle.
Migrating hawks sometimes form kettles, or groups, that will swirl in small flocks overhead.
Hawks swirling in a kettle are actually circling tightly in an air thermal.
When a kettle of birds is tightly circling in a thermal, they look from a distance like something boiling in a cauldron, which may explain the origin of the word kettle to describe a thermaling flock.
Thermals are what the hawks rely on to assist them on their traditional migratory pathways, which are determined by both geography and weather patterns.