I say call because few of us have seen either bird in the flesh (or should I say feather). Both are members of the nightjar family Caprimulgidae which hunt by night and sleep during the day. Your best chance to see them is by slowly driving down a dirt road or lane after dark and watching for yellow or red glowing eyes in the roadway.
If you are going too fast you will catch a fleeting glimpse as the camouflaged bird takes off. Both birds spend the daylight hours sitting on the ground or laying parallel to a sizable tree branch, effectively hidden by their mottled earth tones.
Whip-poor-wills (Caprimulgus vociferus) get the glory because of their vociferous song. According to Whatbird.com, "The record number of calls in a row by a single bird is 1,088, perhaps accounting for their species name, vociferous." I suspect this record was broken at Bull Creek last summer. Vociferous is defined as "marked by or given to vehement insistent outcry" although when it starts outside the bedroom window at 5 AM I would define it as "*@&%$#".
Chuck-wills-widow is more restrained, with a slower, lower song which usually ends politely at bedtime. If you listen carefully to these recordings you will hear the first of its three part song is a "chuck" compared to the "whip" of the Whip-poor-will song.
Both species hunt at night for large moths and flying insects although they are known to swallow whole an occasional hummingbird or warbler when they get hungry during migration. Although their bill is small, they are able to gape their mouth open two inches. Their mouth has bristles which help them to catch all size insects.
They are also called goatsuckers. The name is based on an ancient belief that they fed on goat's milk at night, but their nighttime association with goats and other livestock was probably due to the presence of insects that were attracted to the animals. I would have called them "noisy-suckers".