In large rookeries, several of the other species often come together to live in tightly packed neighborhoods and are frequently joined by double-crested cormorants. Recently dead trees caused by beaver flowages and areas of flooding are choice sites for building rookeries, though colonies may also be built in live trees. One colony I know of on the Turtle-Flambeau Flowage in northern Wisconsin is on an island in thriving red pine trees. Another rookery, Cathedral Pines, is in the top of old-growth white pines. They may also be abandoned for reasons unknown, then rebuilt in another area, or forgotten altogether.
Herons eat mostly small fishes, only a small portion of which are game fish.
Eating small fish has the effect of culling a population of fish so numerous that growth is stunted. Other foods include the delectable wetland smorgasbord of crayfish, frogs, salamanders, snakes, aquatic insects, and rodents. A Great Blue Heron catches a fish. Refuge Reporter . Herons return to their nesting colonies early in the spring, and the incubation of the eggs takes less than a month.