FWIW, Here's my guess:

"Common Nighthawks ...are most commonly seen feeding high in the air during the dusk and dawn hours. Like most other goatsuckers, nighthawks feed on flying insects, but unlike most other caprimulgids (e.g., poorwills) insects are captured or "hawked" during continuous flight. Nighthawks are well-known for the non-vocal "booming" calls which are thought to be produced by air rushing through the primary feathers of males. These sounds are presumably used for courtship display and territorial advertisement."

from http://www.for.gov.bc.ca/RIC/Pubs/teBioDiv/poorw/goatml20.htm

in my experience what is described as a "booming" IS more like a bullfrog.

Lee Cain
Summer: lcain at seasurf.net
School: lcain at astoria.k12.or.us
Instructor, Aquatic Biology/Integrated Science
Astoria High School
Astoria OR 97103 503-325-3911 vm 216

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