Black-crowned Night Heron ( Nycticorax nycticorax ) are small stocky, short-legged compared to other herons. Night Herons are unpopular with other herons, which attack the Night Herons on sight. This is because Night Herons are very aggressive and steal eggs and young of other heron colonies. Perhaps it is the harassment from other birds that force Night Herons to come out mainly at night.
Fact sheet from Ria Tan