Black-crowned night heron along the North Shore Channel in Evanston.RoundTable photo

On a summer’s morning in Evanston, the view from a bridge spanning the
North Shore Channel provides a serene immersion into the natural world.

From a bridge, one may see what the beavers have been up to during the night, ducks that have chanced to land in the still waters below, perhaps a turtle basking in the sun. Birds of all species might be criss-crossing the channel. A Great Blue Heron may be stalking the shoreline searching for its next meal or flying with its majestic, steady wingbeats above the water.

Scanning the trees, one may discover a solitary, beautifully coiffed bird with silver-grey wings, rump and tail feathers, white cheeks and belly, and black on its crown and back. One or more white plumes grow decoratively backward from its nape. It has a red eye and short yellow legs. This bird will be standing stock still  – a great photo op. It is a mature, non-breeding Black-crowned Night-Heron, roosting the day away after its nighttime foraging, before it takes off again at dusk.

But if the morning happens to be during breeding season, the scene about 14 miles south in Lincoln Park will be anything but serene.

Just south of the zoo, Black-crowned Night-Herons (BCNH for short) have established a breeding rookery, having     moved with no explanation from their former location in the Calumet area. Since 2007, these colonial nesters have built their twiggy nests in the park, first on the island in the lagoon and now in sparsely leaved ash trees in the allee near St. Gaudens’ exquisite Lincoln statue just north of North Avenue and Dearborn.

The Chicago Park District has erected a “Do Not Disturb” sign and blocks off the path during nesting season. Because this large group of mallard-sized birds tend to defecate with zeal, this fencing serves as much to protect passers-by as to protect the herons.

Most BCNH migrate, probably wintering around the Gulf of Mexico, although some have wintered on the North Shore Channel. BCNH leave Chicago around October and return in April, often to familiar breeding grounds. Breeding birds are readily identifiable by their pink legs and especially long plumes. Plumes are of extreme importance; experiments have shown that without plumes, finding a mate is nearly impossible. Both sexes look the same, but the male is somewhat larger.

Courtship is a modest affair. Males locate a suitable nesting site, perhaps an old nest, and attract females by bowing, neck-stretching, raising plumes, fluffing their feathers, and ending by bill touching with the accepting female.

The female builds or tidies the nest, with the male bringing more sticks, cementing the monogamous bond for the breeding season. Both sexes incubate the eggs and feed the nestlings. As they switch posts at the nest, their welcome is accompanied by what appears to be affectionate billing and neck stretching. Nestlings first leave the nest after about two weeks and are cared for by both adults for about seven weeks.  Young are brownish and striped. Adult plumage is complete by the third year.

Their comings and goings are impossible to ignore. Although they are called night-herons (their Latin name means “night raven”), during breeding season they must hunt night and day.

Individual birds have their favorite feeding haunts, often along Lake Michigan or inland ponds as far as 14 miles away, where they search for fish and other small live morsels. Adults depart the rookery in groups, squawking in voices likened to a yapping dog with a sore throat.

They forage individually and fiercely defend their own foraging territories. They snag prey and jiggle it until it goes down their heavy black bill head first.

Newly hatched young, usually four or five to a brood, receive a kind of fishy pre-digested juice. As they grow, an entire fish may be deposited in the nest.

Other heron species shun them because BCNH raid their nests for eggs and young. One thought is that feeding at night helps to avoid quarrels with other water birds during the day.

Make no mistake about it: as lovely as these birds are, their nesting habits have both admirers and detractors.

In May 2014, SFGate carried a chilling story about a heron rookery in Oakland, California. “Oakland has come to love the squawking black-crowned night-herons that have taken up residence downtown. Residents say they adore the colony’s rain-forest-like cacophony – a bit of nature amid the hardscrabble urban landscape.”

But the U.S. Postal Service differed. The nesting birds were defecating on mail trucks. During nesting season, USPS hired a commercial company to trim the trees.

Five nestling BCNH were injured when they fell to the ground during the pruning. Irate residents contacted local police, who stopped the cutting. The story blew up to sound like a “massacre.” The herons were reportedly recuperating at a shelter. The tree trimmer, not the USPS, faced charges under the Migratory Bird Treaty Act.

Black-crowned Night-Herons inhabit five continents, all except Antarctica and Australia. Although they are considered Birds of Least Concern by the International Union for Conservation of Nature (IUCN), BCNH have been on the Endangered Species list in Illinois since 1977.

They had survived the hunting and feather craze before the Migratory Bird Treaty act was passed in 1918. (Adults reportedly tasted “fishy;” the young were considered tastier. And the plumes decorated ladies’ hats.)

But there were few rookeries in Illinois, and herons lost much of their wetland habitat in the post-WWII building boom. After the introduction of DDT, they, along with many other birds, suffered from its ill-effects.

Lincoln Park is an ideal location for a BCNH rookery. Nearby Lake Michigan is a perfect source of alewives and other fish, which are the BCNH’s favorite diet. The Chicago River, the North Shore Channel and the wetlands and ponds to the south and west all serve their needs for food.

This year, 263 nests fledged over 600 Black-crowned Night-Herons, a real success story.