Montana Best Times: Big Sky Birding Column

The Fascinating Ecology of the Great Blue Heron: Great Blue Heron or GBH? (September 2005)

The Great Blue Heron (Ardea herodias) is a bird that most people can identify. However, few people understand their fascinating ecology. Inspecting the scientific name of the Great Blue Heron, one finds that both ardea and herodias mean the same thing "heron". Only ardea is a Latin term, while herodias is of Greek origin.

In the world of ornithology, if you try to say the word Great Blue Heron a few hundred times you begin to realize it is a mouthful, so to field ornithologists it is simply called a "GBH". The GBH is the largest of the North American herons, so it is somewhat correct to apply the term "Great", however technically the bird does not have "blue" plumage, but more of a combination of blue and gray colors. This is especially apparent when you see the two tone wing colors when it is airborne. So if you said "there goes a blue and gray heron" you would be technically correct.

Not all Great Blue Herons come in the blue-gray form however. It depends on where you are in North America. In the Florida Keys and the Carribean for instance, some Great Blue Herons are in fact completely white, hence the subspecies called the "Great White Heron". These are basically Great Blue Herons that reside in semi-tropical/tropical marine or salt water environments, but are of a completely different color. Interestingly enough there are even variants or odd color morphs even in "Great White Herons". In the Florida Keys, there is an intermediate form called the "Wurdemann's Heron", which basically has a pure white head and light neck, but the rest of the body color resembles a Great Blue Heron. Wurdemann's Herons are the result of crosses between two races or subspecies, the herodias or Great Blue Heron with the occidentalis or "Great White Heron."

GBH Form and Function
Herons belong to the family Ardeidae, and possess two important morphological features worth mentioning: a pectinate process on the middle toe called a "comb"; and powder down feather tracts found in pairs located on its breast, rump, and flanks which breaks down into a fine dust material and contributes to feather preservation, quality and maintenance. Since herons have only a small oil or uropygeal gland near the base of the tail feathers, they distribute this fine powder or powder down substance from the end of the bill through contacts with the powder down tracts via the serrated comb or claw to all feathers of the body.

Great Blue Herons are easy to identify. Studying a side view in flight, one quickly notices the curtailed s-shaped neck close to the body, with the legs stretched backward extending beyond the tail. Whereas a GBH flying straight towards you or away from you has the classic "^^"(note: I made this by pressing shift 6) pattern that appears in many paintings that try to depict a generic or token bird. The long legs of a GBH are used for wading in different depths of water. The neck remains in the s-shaped position while stalking prey, and has adapted that kinked s-shaped form due to an unusually elongated 6th cervical vertebrae. This allows the bird to strike its prey from a long distance and at lightning speed. Interestingly enough, the trachea or windpipe and esophagus or throat are in front of the vertebrae until it gets to the 6th cervical vertebrae, from this point down it is found in back of or posterior to the cervical vertebrae. This allows the bird to strike at prey at a distance without injurying the delicate trachea and esophagus. The pointed dagger-like bill is used for both hunting and defense.

Stalking Prey
When hunting, the pointed bill can function like a harpoon for spearing or tweezers for grasping depending on the size of the prey. Their typical mode of operation for hunting is the "stand and wait" technique. Oftentimes while driving by in a car, you will notice a tall gray stick protruding out of the water. A closer inspection of the supposed stick, reveals it is a seemingly motionless GBH. However if you watch the GBH, it goes through four general postures when securing food: 1- standing upright to scope for prey; 2- walking slowly, almost in slow motion to the prey; 3-lowering itself and setting up in a s-shaped neck striking position; and 4- the lightning strike speed at the prey.

GBH's specialize in calm, slow-moving, fresh water or sometimes brackish or even thermal water environments. They feed on a variety of live prey depending on the season and the locality. One often associates this bird with feeding almost exclusively on small fish, but closer scrutiny of its feeding behavior finds it preying on other organisms such as insects, amphibians, snakes, small mammals and even young birds. If they eat mammal hair or large scales from fish, they have the ability upchuck or cast a pellet such as occurs in raptors . Occasionally, GBH's have been known to choke to death swallowing very large prey. So the next time you see a GBH, take a few minutes and try watching the fascinating ecology and behavior of this remarkable bird.

Now that the reader has a better understanding of a part of the ecology of the Great Blue Heron, the next topic scheduled for the November issue of Montana Best Times will be about nesting and Great Blue Heron nesting colonies, and their status in North America.

Enjoy! And the Best of Big Sky Birding to you!