(Nycticorax and Nyctanassa), so called from the fact that they are mainly nocturnal in their habits, are medium-sized Herons, ranging from eighteen to about twenty-four inches in length, of very stout, thick build, with large, thick heads and very thick bills. The prevailing colors are bluish gray, black, and white; but the plumage of the mature birds is exceedingly different from that of the young, being in the latter mainly brownish, striped longitudinally with white; the sexes are, however, similar in each stage, while in the adults there are two or three exceedingly long, thread-like, white occipital plumes.
About a dozen Night Herons are known, two forms being found in North America. The genus is nearly cosmopolitan, except that it does not range very far north. Perhaps the best-known, and certainly the most widely distributed, species is the Black-crowned Night Heron (N. Nycticorax), which ranges from central and southern Europe to the Indian peninsula, China, Japan, the Malay Peninsula, and Africa, and the American form of it which is found from the British possessions to the Falkland Islands and the West Indies.