At various places along the North Kona and South Kohala coast there are pools just inland from the coast. Many of these pools are connected to the ocean and serve as breeding grounds for fish. In the larger pools those fish can be quite large. And where there’s a large pool of water with fish in it, herons won’t be far away.
The bird in the top photo was actively hunting, while the other was merely monitoring the situation. These adult birds have the black crowns that juveniles lack and also sport a long, white head plume, that I think is rather elegant.
Black-crowned night herons are considered indigenous because they weren’t introduced to Hawaii, but arrived on their own hundreds of years ago. Thus far, they haven’t changed from their mainland counterparts.