March Species Spotlight: Great Blue Heron

One of the most majestic water-going birds in the United States is the Great Blue Heron (Ardea herodias). The Great Blue Heron (GBH, hereafter) is the largest wading bird in North America, standing at about three feet tall. It is often mistaken for a crane because of its size and shape. This heron, like many other waders, has long legs for walking through deep water, mud, and vegetation. It also has a long neck to match. The head is topped with a black crown which extends into long, elegant head plumes. The bill is long, pointed, and bright yellow. The immatures look similar to the adults except their plumage is browner, often appearing dingy in comparison. The well-developed head plumes and brightly colored bill are lacking on young individuals. These birds have a huge wingspan, reaching up to six and a half feet. In flight, look for arched wings, outstretched legs, black flight feathers, and a neck kinked into an “S” shape. They occasionally call, giving a deep, raspy cronk. They sound much like how I imagine a prehistoric dinosaur would!

The typical “blue form” is a cool, blue-gray all over, but the GBH can exhibit some other color variations. The white form, sometimes called the “great white heron,” has entirely white plumage. It is found in small populations in Florida and Mexico. This form looks incredibly similar to the Great Egret (Ardea alba). The other color variation (also found in southern Florida) is called the “Wurdemann’s” heron. It has the body of a dark (blue) form with the head of a white form.

Their range covers most of North America. They are distributed from southern Canada all the way to their wintering grounds in Central America. The GBH can even be found along the Pacific coast all the way up to Alaska. Some populations at the northern end of their range are migratory, flying south as winter approaches. Otherwise, many populations across the United States are year-round residents.

The Great Blue Heron can be found in a variety of aquatic habitats. Ponds, rivers and streams, marshes, tidal flats, swamps, and shores are a few places you may find this heron. It uses its long neck and sharp bill to catch prey. The GBH stands perfectly still while hunting, waiting for an unsuspecting fish to pass by. When the fish is close, the heron spears it in one sweeping blow. Thanks to special vertebrae in the neck, the heron is custom-made for jabbing prey. In the blink of an eye, the prey is swallowed whole. Fish are not the only critter on the menu. They also dine on amphibians, reptiles, birds, small mammals, and invertebrates. Since the GBH is so much larger than other waders in North America, they can venture into deeper waters and catch larger prey than their smaller heron and egret cousins. They are skilled hunters in both light and dark conditions due to a high number of special photoreceptors in their eyes. Hunting in slow-moving or stagnant water can leave a nasty layer of grime on the bird’s feathers. The heron has specially fraying feathers which are brushed and gathered with pectinations (bristles) on the middle toes. It uses the “powder down” like a rag to wipe off the grime and fish oils while it preens.

Even though they like both freshwater and saltwater habitats for foraging, they prefer to nest over freshwater. Nesting over water deters predators from raiding eggs or nestlings. Their nests are huge formations (up to 4 ft across) constructed of sticks. It is typical to see the huge structures high in trees, but they also nest in lower vegetation, on the ground, and on human made platforms. They usually form a colony with conspecifics or other waders. These colonies, also called heronries or rookeries, easily contain hundreds of nests. In fact, some have been known to reach an astounding 500 nests! The GBH generally mates for life. Their courtship and territory displays are quite intriguing, consisting of outstretched wings, raised plumage, and interesting body movements.

GBHs generally do not mind human presence as they are commonly found in water near human-built structures. However, too much close contact with people can cause the adults to abandon their nests. Within the last half century, the number of breeding GBHs has risen. This increase is due, at least in part, to beaver activity. As beavers dam up waterways, they create the slow-moving, shallow water habitats that this heron finds favorable. Even during recent increases, destructive human activities, chemicals, and habitat degradation still pose threats to the heron.

Because the GBH eats fish, some hatchery workers voice concern over these birds decreasing cultivated fish populations and profitability. Herons may actually be benefiting fish farms. When fish are sick or diseased, they spend more time at the water’s surface. The herons easily pick off those individuals, eliminating the sick and dying from hatchery populations.

The Great Blue Heron is an interesting and charismatic species. Being so widespread and conspicuous across North America, it is the favorite of beginning and experienced birders alike.

Sources:

Great Blue Heron_Wildlife Profile_FINAL.pdf (ncwildlife.org)

Great Blue Heron Identification, All About Birds, Cornell Lab of Ornithology