As this photo shows, they are very well camouflaged, and that apparently serves them well.
Despite their name, nighthawks are not raptors; they are insect-eaters, and soar in the evening, gathering flying bugs into their very wide mouths with the help of "whiskers." The young are semi-precocial, which means that after they are hatched they do not need the constant care of a parent, as many nesting birds (doves, robins, etc.) do, but can move about and hide. They still depend on their parents, however, to bring them food until they are strong enough to fly on their own.
When a birder and I saw the nighthawk today on our bird walk, she seemed fidgety. We wondered if it was due to all the bugs brought out by the extreme humidity, but apparently she was just getting ready to resettle herself and turn her eggs:
Which she did, and which we were lucky enough to observe and videotape. By the way, birds such as nighthawks and doves that nest in the desert sun in the summer do so to keep their eggs COOL.
Here's the video: