Much in the same way that "woodpeckers" have evolved several times (most are birds that look like each other, but then there is the aye-aye and Darwin's finch), one can say that the nightjars are birds poking around in the insect-eating bat niche.
Nightjars are crepuscular birds also known as goatsuckers. The most commonly seen nightjars in the US are probably nighthawks. The Whip-poor-will is one. If you've traveled much in Africa, then you may just know of them as "Nightjars" as in "Whoa, Rafiei, what was that bird that just flew out of the dirt road past our headlights?" ... "That was a Nightjar. They are everywhere on the roads at night."
Technically, these birds form the order Caprimulgiformes, which includes the families Caprimulgidae (nightjars, nighthawks, whip-poor-wills, and the Pauraque) with about 100 species; the Podargidae (a.k.a. "frogmouths") with 17 species, the Nyctibiidae (Potoos) with 7 species, and the Steatornithidae (or Oilbird), with a single species. Collectively, this order is among the most interesting and, dare I say it, bizarre, of all the birds.
They are represented on all continents except Antarctica, with the greatest diversity in South America.
There is one species of nightjar that uses echolocation. There is a handful that hibernate, and others that enter torpor. They are all crepuscular and/or nocturnal. Most exhibit the interesting behavior of not flying or running away when discovered in their roost. Rather, they just sit there and assume that you can't see them. Given their incredibly cryptic plumage, that is probably almost always the case, but ornithologist have been able to study many Caprimulgiformes by finding them and just picking them up to have a closer look, as the bird sticks to its story that it doesn't really exist.
Nightjars, Potoos, Frogmouths, Oilbird, and Owlet-nightjars of the World, by Nigel Cleere, is a new publication that describes the behavior, biology, conservation status, geography, and taxonomy of this group of birds in a few dozen pages followed by a species description, each with several photos and a nice map, of every species around the world. This is the orthogonal approach to a regional field guide: Instead of having one book for all the birds in your region, you have one book that will identify any bird in large taxonomic group for anywhere in the world that you go. Of course, to have full coverage using this method, you'd better bring a truck!
But that's not really the reason to have a book like this (which, I was shocked to find, is quite affordable for a major monograph with almost 600 color photos in it). The reason is to embark on the detailed study of the taxonomy, behavior, evolutionary biology, etc. of one taxon, in order to enrich your overall birding experience. (I've made this suggestion before.)
And, the pictures (a sampling of which I've gratuitously placed in this post) will blow your mind.
Is your "T" key sticky, or are "nighjars, nighhawks" (para 3) actually acceptable substitute names for "nightjars" and "nighthawks." They might be for all I know.
Its Scottish, OK?
Commented on an earlier post that we weren't seeing nighthawks in numbers in Wisconsin ... well the migration is here - several hundred (!) passing the last week or so.
I once heard an Australian researcher say that the way you find tawny frogmouths is to go out into some farmland and look for suspiciously tall fenceposts. He spent the rest of his talk taunting us with pictures very similar to the 4th one in this post.
Excellent post with a catchy title. The Illinois Natural History Survey has a Nightjar monitoring program called "MOON".
We are lucky here at our forest-home in South East Queensland, Australia, to receive visits from the highly endangered Marbled Frogmouth; an extremely beautiful member of the family.
I had no idea you had such a diversity of Nightjars in America, I would love to see them. In England we have one - I took a video of ringing one caught in mist nets in my inlaws' garden