There are approximately forty species within this family, and they have basically a global distribution (with the exception of some oceanic islands).
In terms of whether or not a member is a cormorant or shag–that depends solely on whether they have a ‘crest’ or not. This came about from Great Britain, where both the great cormorant and common shag are found–the common shag has a crest, and the great cormorant lacks one. Not the best naming system–but it is the one that has been around the longest.
There is one flightless species: the Galapagos cormorant, which became the largest living member of the family after explorers and sailors drove the spectacled cormorant (which was a flightless cormorant found on Bering Island within the Komandorski Islands) to extinction in the 1800s.
All members of the family feed on fish, which they may (or may not) have to chase under water. They all have short wings (compared to the rest of their bodies), and heavy body mass (helps in diving) when compared to other sea birds. Though their feathers are not totally water proof (like say a pelican or duck), which is why you will see them sitting atop trees, rocks, and other items with their wings spread out drying off after a hunt.
These birds seem to have kept the ancient avian body plan (short wings, long neck, heavy bones), though the evolutionary details of the family origins are still semi-unknown (the lighter the bird bones the less likely they are to have fossilized). These issues are a contributing factor to the constant reorganization of the classification system of birds.
Members of the family that can be spotted along a coast (or within) the United States, Canada, or Mexico include the:
Great Cormorant
Double-crested Cormorant
Neotropic Cormorant
Brandt’s cormorant (shag)
Pelagic cormorant (shag)
Red-faced cormorant (shag)
Photography goals for this family include: getting a picture of the other members that can be spotted along a coast (or within) the United States; and then trying to get a picture of one along the coasts of the other continents. Bonus points for getting to the Galapagos Islands and getting a picture of the last remaining flightless member of the family.
Reference: https://en.wikipedia.org/wiki/cormorant