Қос тоқылдақ қара қаздың сипаттамасы

Species of bird

The double crested cormorant (Nannopterum auritum) is a member of the cormorant family of water birds. It is found near rivers and lakes and in coastal areas and is widely distributed across North America, from the Aleutian Islands in Alaska down to Florida and Mexico. Measuring in length, it is entirely black except for a bare patch of orange yellow facial skin and some extra plumage that it exhibits in the breeding season when it grows a double crest in which black feathers are mingled with white. Five subspecies are recognized. It mainly eats fish and hunts by swimming and diving. Its feathers, like all cormorants, are not waterproof, and it must dry them out after spending time in the water. Once threatened by the use of DDT, the numbers of this bird have increased markedly in recent years.

The double crested cormorant is a large waterbird with a stocky body, long neck, medium sized tail, webbed feet, and a medium sized hooked bill. It has a body length of between long, with a wingspan of between Double crested cormorants weigh between Males and females do not display sexual dimorphism.

The double crested cormorant swims low in the water, often with just its neck and head visible, and dives from the surface. It uses its feet for propulsion and is able to dive to a depth of for 30–70 seconds. After diving, it spends long periods standing with its wings outstretched to allow them to dry, since they are not fully waterproofed. This species flies low over the water, with its bill tilted slightly upward, sometimes leaving the colony in long, single file lines.

Food can be found in the sea, freshwater lakes, and rivers. Like all cormorants, the double crested dives to find its prey. It mainly eats fish, but will sometimes also eat amphibians, crustaceans and insects. The population may have also increased because of aquaculture ponds in its southern wintering grounds. The ponds favor good over winter survival and growth. In 1894, Thomas McIlwraith in his book, Birds of Ontario, concludes his section on double crested cormorants by saying: "When the young are sufficiently grown, they gather into immense flocks in unfrequented sections, and remain until the ice lid has closed over their food supply, when they go away, not to return till the cover is lifted up in the spring." For populations nesting in the Great Lakes region, it is believed that the colonization of the lakes by the non native alewife (a small prey fish) has provided optimal feeding conditions and hence good breeding success. Double crested cormorants eat other species of fish besides alewives and have been suspected of contributing to the decline of some sport fish populations in the Great Lakes and other areas. In May 2008, the Canadian government reduced significantly the number of nests of the birds on Middle Island, a small island in Lake Erie and part of Point Pelee National Park. This is an attempt to keep the small island in balance and preserve its vegetation but opponents to the plan have argued that it is based on faulty information, provided in part by anglers who view cormorants as competitors. As of 2021, the cormorant culling program continues.