Common Nighthawk at Malheur NWR, Oregon on 30 May, 2010 by Greg Gillson.[Click to read all Memorial Day weekend at Malheur posts.]
Common Nighthawk is usually the latest regular spring migrant to arrive in the Pacific NW. The first few usually arrive by Memorial Day weekend, but the bulk don't arrive until June. They sit horizontally on branches, wooden fence rails, refuge signs, and gates (as above).
Not really nocturnal, and not a hawk at all, these crepuscular insect-eating birds are camouflaged to hide them during the day.