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Toning effects for those fish populations. Night herons help tone crustacean


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River-Lab 5 Guide Manual

BLACK-CROWNED NIGHT HERON (Nycticorax nycticorax)
This bird’s appetite is an important contribution that helps keep a basin system healthy. Night heron predation on medium to large fish, which make up fifty to eighty percent of its diet, has valuable toning effects for those fish populations. Night herons help tone crustacean populations in both fresh and salt water. They also help control some fish, insect, and rodent populations. Adult night herons are not known to have any predators, but their young are eaten by a few animals, including some people.
The night heron helps keep at least one potentially over-populating fish species in balance with the rest of the life in a basin system. They regularly follow the spring runs of large coastal fish called alewives as these fish move up into rivers to spawn. Because alewives tend to be overly-reproductive, predation is needed to keep their numbers in balance with other species of fish. A night heron is ideally suited to eat alewives. Adult alewives are a very bony meal. Strong chemicals in the heron’s digestive system can dissolve both the scales and numerous bones of this fish. Because of their boniness, alewives are not a preferred meal for other predators, including people.
Night herons also prey on and tone the populations of freshwater crayfish, and saltwater crabs and shrimps. Night heron consumption of aquatic insects and, to a lesser extent, of mice and rats, is a valuable contribution to the control of these organisms whose high rates of reproduction can cause imbalance and upset the basin system of life.
Night herons fish by making a lunging dive from a standing position on a bank or muddy edge into shallow water. Their awkward-looking grab almost always results in a catch. The night heron will then toss its prize into the air, so that when recaught in the heron’s bill, it will slide head-first down through the heron’s open throat.
Night herons are not usually in direct competition with kingfishers, since herons eat larger fish (up to 14 inches). Nor do night herons seem to mind sharing fishing areas with gulls, which catch female alewives and rip open their bellies to eat the roe (eggs). Night herons will, however, grab fish out of another heron’s mouth. This often occurs when they are following the first runs of alewives upstream in April.
BLACK-CROWNED NIGHT HERON, cont’d.
The black-crowned night heron is a medium-size (23–28 inches tall) chunky bird with short yellow legs and a thick, black bill. It has a black back and cap that contrasts with its gray wings (44-inch span) and white or pale gray underparts. Three eight-inch long white plumes stretch from the back of its cap down its back. During breeding season its legs turn pinkish.
The night heron’s call, a loud, barking “quok,” is most often heard at dusk when it begins to fish. Large groups, or colonies, of these birds roost in the tall trees in or near wetlands, ponds, and rivers. They usually sleep by day and fly up and down inland and coastal waterways at night, wherever fish and other kinds of food are available.
Night heron nests (sometimes eight in one tree) are platforms of sticks. These are scantily lined with finer material. The female lays three to six pale dull blue eggs

(1 2/5 x 2 inches), which are incubated by both parents for 24 to 26 days. The young are practically helpless for the first three weeks. They anxiously squawk, squeal, scream, grunt, croak, or bark as they wait to be fed. Since these birds live in colonies of twelve to fifty nesting birds, their combined night noise can be very loud.


Young night herons will be on their own when they are half-grown. At this stage they are streaked brown and white and have lighter bills. Those that do not become a meal for a crow, raccoon, or other predator will learn from observing adults in the colony. They will develop into fully participating members of this somewhat comical but no less valuable segment of the basin system of life.


5GM – 31 © 1999 Mill River Wetland Committee, Inc.


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