Standing motionless on a shallow river bottom or in a pond, the Great Blue Heron can be almost invisible. Its solitary erect, slim, stately four-foot figure mimics the twiggy background. It peers intently into the water, seeking to spear a fish, its favorite prey. It may stride slowly and deliberately, spreading its weight among its four toes. The first two have vestigial webbing between them, keeping the bird from sinking into the muddy shallows. Its stride makes hardly a ripple.
If disturbed, it will ascend with a loud, unmusical “squaaawk” and then commence one of the most beautiful of all bird flights: long body outstretched, long neck folded back like an S, long yellow bill pointed straight out, long dark legs trailing behind, six-foot rounded wings extended and beating slowly and deeply as if rowing the air. Poet Paul Farley writes of the heron’s “begrudging avian takeoff”:
It “struggles into its wings then soars sunwards and throws its huge overcoat across the earth.”
Its local name in western Maine is “meadow hen,” because herons forage the wet fields for amphibians, invertebrates, reptiles, insects, mammals, and birds. They swallow their prey head first. Great Blues feed day and night, protecting a small foraging territory about several hundred yards in diameter.
Herons’ almost panoramic sight has been the subject of much study. The heron’s challenge is to strike moving prey within a maximum of three feet from its eyes while standing still. It gets one chance. With its bill held in a horizontal position, its bifocal vision can focus at its feet, awaiting a fish to swim within range. Simultaneously, with its monocular vision, through eyes set wide apart well back on the sides of its head, it can scan different scenes on each side for threats. Additionally, a bird that relies on hunting over water must contend with glare from the sun. One study suggests that herons tilt their heads to solve that problem.
Their long legs illustrate how birds walk to achieve balance and spring on takeoff. Birds walk on the tips of their toes with the rest of the foot raised off the ground. What looks like the heron’s shin is the equivalent of the arch of our foot. What looks like the heron’s knee is the equivalent of our heel/ankle joint. Its real knee is hidden under the feathers.
Worldwide, there are about 60 species of herons in the family Ardeidae, which includes all herons, bitterns and egrets. They inhabit salt or fresh water and live on every continent except Antarctica and in every habitat except very dry deserts, very high mountains and the coldest arctic. The Great Blue Heron, the largest heron in North America, is found only in the western hemisphere: in Alaska, Canada and south through Central America. Great Blue Herons are extremely adaptable, their variable diet accounting for their ability to winter farther north than other herons.
In contrast to their lonesome foraging, they nest in noisy colonies in trees, usually on islands or in swamps that offer some protection against ground predators. They will fly about four miles to their favorite feeding grounds.
The male arrives first sometime in March and flies straight to a rookery to claim an existing nest or empty perch. He launches into an elaborate courtship display returned by the female. Once mated, the pair is monogamous for the season. The male brings the female sticks with which she constructs a twiggy platform nest. A first-season nest can be a flimsy affair, but nests used repeatedly can measure almost four feet across and more than three feet deep, strong enough to withstand gale force winds. Nests are lined with soft material and added to throughout the nesting period.
Both sexes take turns incubating the eggs for about 25-30 days. The male generally incubates during the day, the female taking a shorter night shift. Eggs hatch in the order in which they are laid. Consequently the oldest nestling has the advantage of being better fed and stronger; the youngest has the least chance to compete successfully. Although fledglings can fly at about 60 days, they generally stay with their parents for two to three additional weeks.
Male and female Great Blue Herons look alike. Adults have grayish blue feathers, a white face and crown, and black eye-stripes that extend to the rear as slender plumes. Their long bills are thick and dagger-like. They have black patches on their shoulders. Their long necks are decorated with a vertical band of black, white and brown streaking on the front, the rest of the neck being a smooth light rust-brown. White plumes extending from neck, breast and back give older herons a decidedly shaggy look. Long stilt legs are dark with chestnut thighs. Immatures lack black shoulder patches and have a solid black cap.
All herons have a middle toenail outfitted with a small comb used to groom and keep the feathers and bristles around the beak free of parasites. In addition, on their breasts they have two patches of “powder down,” mats of short feathers that grow continuously and disintegrate into a yellowish powder. The purpose is unknown but some observers speculate that the bird wipes the powder over the feathers to clean them.
In Evanston, Great Blues frequent Northwestern’s lagoon and the North Shore Channel. Two active rookeries are at Baker’s Lake in Barrington, near the intersection of Northwest Highway and Hillside Ave. and at Almond Marsh on Rte 120 in Grayslake. Both colonies have manmade nesting structures on islands to substitute for the original trees.