To see the scap pattern of a Common Poorwill, gray with anchor shaped markings, go to
http://www.utahbirds.org/birdsofutah/Profiles/CommonPoorwill.htm
This photo also shows the throat and auriculars as being of the same color - blackish
To see the more prominent silvery scaps of a Eastern Whip-poor-will, with black blotches at tips go to
This also shows the browner auriculars contrasting with the black throat
It is hard to find good photos of undertails of either species, particularly Common Poorwills, so I find myself stymied as to that mark, but I really see little to make me think this bird is a Whip other than its peculiar habits.
Respectfully
Steve Mlodinow
Longmont CO