There are two species of bitterns seen in North America, they are the American Bittern and the Least Bittern. The Yellow Bittern, is a vagrant from Asia, that has been spotted.
Bitterns live in the marshes and along lagoons and waterways, preferring long grasses and cattails. With their deliberate skulking and their brown and tawny feathers, these birds become almost invisible to the naked eye. The American Bittern has a unique call, which is quite similar to the sounds that water makes in a backed-up drainpipe.
The Least Bittern is most often seen in the southeastern areas of North America. Because of its small size, it is more likely to be heard than seen, whereas the American Bittern can be found all over the continent except in the tundra and far North.
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.