As the name suggests, this species is largely nocturnal, spending most of the day resting in secluded places and then coming out at night to forage. They typically feed on fish, frogs, and other aquatic animals but may take a variety of other items if they are available. They were fairly common in some of the larger marshes in northern Iowa until several decades ago but in recent years their numbers seem much reduced and no large nesting colonies are known in the state. The reasons for this apparent decline are not known. Black-crowns typically nest in colonies that sometimes number 100 nests or more. Their nest is a simple platform of reeds or twigs, placed either in the crotch of a tree or on a mat of dead aquatic vegetation.
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indicates a designated IBA.