Great Blue Heron Rookeries

Most all of us who wander the woods and wetlands are familiar with the striking and solitary figure of the Great Blue Heron. A very large, slender bird patiently posed at the water’s edge, ever vigilant for the motion of fish in the stream, but what is less apparent about these great birds, the largest herons in North America, is their complex social structure.

The Great Blue Heron’s choice of habitat is variable due to the adaptable nature of the bird itself. A quick check of any competent ornithology site shows a range map encompassing most of southern Canada as summer reaches of Great Blues with much of the United States as “all season” and most of Mexico as “winter habitat.” Before we venture into the Nesting Colonies of these very large and unique birds it is interesting to note their broad areas of habitat, including their ability to nest further north than other herons, is due to their variable diet. Seattle Audubon Society tells us this about the diet of Great Blue Herons, “Fish, amphibians, reptiles, invertebrates, small mammals, and even other birds are all potential prey of the Great Blue Heron. In Washington, much of their winter hunting is on land, with voles making up a major portion of their winter diet.” That fits with the pattern of the males propensity of being more shoreline foragers leaving the females and juveniles to hunt in more upland areas.

It is the male of this avian species that gathers the bulk of nesting material, indeed the males are the first to arrive at long established colony nest sites. From old nests or potential nest sites the male Great Blue Heron courts the passing females, using calls, posturing and flight maneuvers to gain her approval. Once a pair bond the male presents the new nest materials to the female, who will begin weaving a large bowl like nest that she lines with grass, pine needles, moss or other suitable soft materials. This process can take from a few days up to a couple of weeks, with the resulting nests reaching several feet across.

Great Blue Herons have intricate behavioral traits, which I’ll turn to Cornell Lab of Ornithology to describe “If you visit a colony, look for elaborate courtship and pair-bonding displays that include a ritualized greeting, stick transfers, and nest relief ceremony in which the birds erect their plumes and “clapper” their bill tips. Pairs are mostly monogamous during a season, but they choose new partners each year. Away from the colony, Great Blue Herons defend feeding territories from other herons with dramatic displays in which the birds approach intruders with their head thrown back, wings outstretched, and bill pointing skyward. Gulls and even humans may also be a target of this defensive maneuver.”

Here in the Pacific NW a Great Blue Heron rookery is generally on a forested island, within either a saltwater estuary, lake or river, generally in a remote location (although human habitation has grown up around many long occupied heron nest colonies). Colony sizes vary from several dozen birds to hundreds. Washington State is home to a number of heron rookeries or “heronries”, with some being fairly easy to observe. You’ll need a good pair of field glasses, and a bit of determination to have an enjoyable bit of time observing these large and very unique birds in the wilds of Washington State.

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