Black-crowned night herons do not fit the typical body form of the heron family. A friend told me this chappy looks sad...ahhhhhhhh
They are relatively stocky with shorter bills, legs, and necks than their more familiar cousins, the egrets and "day" herons. Their resting posture is normally somewhat hunched but when hunting they extend their necks and look more like other wading birds.
As mentioned, shooting in an urban park is a great way to get close to these wild birds.