There are at least five different groups in the nightjar family seen in North America. These include the whip-poor-wills, Common Poorwill, Common Pauraque, Chuck-will's-widow, Buff-collared Nightjar and the nighthawks.
The 9 bird species in this group are the Eastern Whip-poor-will, Mexican Whip-poor-will, Common Poorwill, Common Pauraque, Chuck-will's-widow, Buff-collared Nightjar, Common Nighthawk and the Lesser Nighthawk.
Nightjars can be identified by their calls which are different from one another. These calls usually start just before darkness and carry on into the night. All nightjars are insect-eating birds and they catch most bugs on the fly.
Avibase - the world bird database This site provides the user with a complete list of bird species, broken down per country, or in the example of the US or Canada, per state and province. Here, bird species names are available in other languages, a great asset to be used as a translation of foreign bird names.
ABA - American Birding Association This site represents an organization that maintains official records of all birds species that have been proven to have been seen inside the perimeters of the North American Continent and the surrounding bodies of water. Regular revised versions are posted to keep the bird list current at all times. This is the list used by all serious birders over their lifetime. You may be aware of the movie called the "Big Year". It was with this list that all the competing birders used in an attempt to set a new record as to how many bird species that could be seen by an individual birder in one calendar year.
I hope you will take advantage of these suggested websites. I have used each of them, in one way or another, throughout the years in my quest to better identify and understand our fine feathered friends.