Great Blue Heron

Common Name: Great Blue Heron

Scientific Name: Ardea herodias

Appearance: The Great Blue Heron is the largest and most widespread heron in North America (length 40-50 inches; wingspan 77-82 inches). Adults of both sexes are similar in appearance, distinguishable by mostly gray plumage with a white throat and head, and a black cap. The underparts are a lighter whitish-gray and the black sides often appears as black shoulders when the birds are perched. Adults have yellow eyes, a yellow-orange bill and flesh-colored legs. Juveniles have duller eyes, a darker upper bill, and lack the dark sides. The white morph of this species (The Great White Heron) has entirely white plumage.

Habitat/Where to find: The Great Blue Heron is widespread in North American freshwater and brackish wetlands including marshes, swamps, lakes, rivers, mangroves. The Great White Heron is found only in marine habitat, primarily in the Florida Keys. Both morphs interbreed freely, and the hybrid form (Wurdemann’s Heron) is common in southern Florida. The Great Blue Heron breeds as far north as southeast Alaska, the central Canadian prairies, and the Canadian maritime provinces. They breed as far south as Florida, Texas, Baja California, and Belize. They winter south of the Midwest, as far as Colombia.

Sounds: Although the Great Blue Heron is considered our most vocal heron, it is still mostly silent. They vocalize the most at nesting colonies, but their vocal repertoire is relatively limited, and can best be described as a range of squawks and croaks. They most frequently vocalize in flight, producing a deep-throated “fraaahnk” or “rroh”.

Behavior: Except when breeding, the Great Blue Heron is mostly solitary and nocturnal. In flight they fold their long necks into a compact S shape, with their legs juting out behind their tails. When foraging, they are strongly territorial and will react aggressively towards other herons that approach. Males produce elaborate courtship displays at the nest by stretching their long necks, fluffing their feathers, and making circle flights. Mated pairs display together by raising their crests and clappering their bills.

Reproduction: The Great Blue Heron breeds monogamously in large colonies, sometimes in colonies of mixed species. Breeding colonies are most often located on isolated islands or swamps to help protect from mammalian and reptilian predators. They build large stick nests situated high in trees, but also sometimes iplace their nests in shrubs. The female lays 2-7 bluish-green eggs, and each pair raises a single brood per year.

Food Habits: Great Blue Herons can be frequently observed hunting along the edges of waterways, in slow moving water, and sometimes in grassy fields. They search for prey by creeping around very slowly, or waiting motionless for long periods of time until an animal nears -- and then quickly striking their prey. Their diet is composed mainly of small fish, amphibians, reptiles, and small mammals. They will also feed opportunistically on a wider variety of foods including human food scraps and bird nestlings.

Vital Statistics: Most Great Blue Heron nesting attempts are successful (69% produce at least one fledgling), and most successful nests fledge at least two young. Juvenile Great Blue Herons suffer relatively high mortality in their first year (69%), but fare better in the second year (36% mortality), and even better in subsequent years (21% mortality). The oldest known Great Blue Heron (from banding records) lived to at least 23 years of age.

Migration/Dispersal: Great Blue Herons that migrate include those breeding in Canada, the Midwest, and other northern parts of their range. Some of the northern migrants winter on the Pacific coast, but Pacific coast residents appear to be nonmigratory. After breeding in the spring, some birds venture briefly into northern Canada and the Alaskan Arctic. South-bound seasonal migrants leave their spring and summer grounds anytime from mid-September to late October. Great Blue Herons return to the Midwest in February, and return in mid-March to Canada and the northeast.