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Birds of the Night - Black-crowned Night-Heronsby Ruth Ann AngusI spied it out of the corner of my eye - a stalking movement of something down on the rocks, below the bayside walkway outside of Marina Square in Morro Bay. What was it? It was early evening and the sun had already slipped below the horizon. It was the perfect time for the creatures of the night to begin their daily hunt. Black-crowned Night-Herons choose just this time to begin searching for the tasty morsels that make up their diet. And it was a Night-Heron that I saw on the rocks. The bird stood stock still, eyes fixed on something hidden deeply in the rocks that I couldn’t make out. Would he get it? After concentrating intently, the heron began to stretch its neck forward ever so slowly. Several more seconds passed and then - zoom - the Night-Heron struck. The victim was something dark, long, and narrow. I thought it might be an eel, but was not sure if there are eels in the bay. I checked in one of my guides, finding two fish fitting the description of this prey. The cockscomb and the prickleback resemble small eels and are long and narrow. They’re both found under rocks and in tidepools. It might have been one of these that the Night-Heron caught. As the name implies, the Black-crowned Night-Heron is a nocturnal bird that hunts at night in order to avoid competition with the day herons that frequent the same habitat. It’s a stocky bird, not as large as its cousins - the Great Blue Heron and the Great Egret. It has a short neck and legs and is often seen hunkered down with its head tucked into its body. Adult Black-crowns have beautiful coloration, with steely blue-gray wings, rump and tail, and white to gray underparts. Their legs are yellow except for breeding season, when they turn a pinkish color. They are named for the black cap that extends down onto the upper back and scapulars. A pair of white plumes extends from the back of the head. The most distinctive feature is the eye, which is an intense red. Juvenile birds are streaky brown and buff-colored with gray legs and yellowish-amber eyes. It’s thought that night herons are monogamous with life-long pair bonds. Breeding behavior begins with the male becoming aggressive and performing snap displays where he walks around in a crouched position, head lowered, snapping his mandible together or grasping a twig. He then goes on to the stretch, using snap-hisses or song and dance displays in which he stretches out his neck and bobs his head. When his head is level with his feet, he gives a snap-hiss vocalization. Twig shaking and preening occurs between songs. All of this is performed to attract a female. As a by-product, the behavior lures other birds into displaying also. Males actually reject the first females that come into their displaying territory, but eventually a pair formation occurs. Night-Herons nest colonially with a dozen or so nesting in one tree. They are often found in rookeries along with Great Blue Herons and Great Egrets. The male collects sticks and presents them to the female, who works them into a platform nest. Eggs are laid at two-day intervals and incubation lasts 24 to 26 days. Both adults sit on the eggs. The clutch size is three to five eggs that are green on the first day and turn pale blue or bluish green after that. Two weeks after hatching the young leave the nest but don’t wander far. Then they gather together in juvenile bands roosting at the tops of the trees. By the seventh week they can fly well and depart for feeding grounds. Night-Herons feed on fish, earthworms, leeches, aquatic and terrestrial insects, crustaceans, snakes, lizards, rodents, and even young of other nesting birds. Their digestive acids are so strong that the bones they consume are dissolved in their stomachs. To attract water dwelling prey, the birds use a technique called “bill vibrating” that involves opening and closing its bill rapidly in the water. This creates a disturbance that may lure prey. Black-crowned Night-Herons do migrate in large flocks traveling at night and resting during the day. Spring migration is from mid-February through mid-May and fall migration occurs from mid-July through October. My Night-Heron couldn’t hang onto its catch, which snaked and slithered away into the water. The heron was left standing on the rocks, seemingly mystified as to what had happened.
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