A caller into 'Coast To Coast" with host George Knapp Sunday June 20, 2010, toward the end of the first hour was talking of UFOs he has seen and being short of time only indicated that one type he has seen in the area of Billings, Montana is what he described as a "ring/doughnuts, landing in cottonwood trees".
The caller was enouraged to write an email to George Knapp describing the UFOs the caller has seen. Perhaps more will be learned of what the caller exactly saw when he saw these "ring/doughnuts", whether they are related to the "California Drones" of three years ago.
The only idea I have for why they might "land" in trees is to hide their presence, not so much to actually "park" themselves.