Double-crested Cormorant
From Freepedia
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| Phalacrocorax auritus (Lesson, 1831) |
The Double-crested Cormorant, Phalacrocorax auritus, is a North American member of the cormorant family of seabirds.
This is a very common and widespread species. It breeds in coastal areas as well as near inland rivers and lakes, building a stick nest in a tree, on a cliff edges or on the ground on suitable islands. They are gregarious birds, usually found in colonies, often with other aquatic birds. Their call is a deep, guttural grunt.
This bird feeds at sea and on freshwater lakes and rivers. It winters anywhere along the coasts that is well supplied with fish.
This is a large black bird 74-91 cm (29"-36") long, with a wingspan up to 132 cm (52"). It has a long tail and a yellow throat-patch, and can appear to have a green sheen in certain lighting. The white double head crest is seen for a short period during the breeding season in western birds. It is duller in eastern birds. Juveniles are brown with a white face, foreneck, and breast.
Like all cormorants, the Double-crested dives to find its prey. It eats mainly fish, but also amphibians and crustaceans. This bird 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 1.5-7.5 m (5-25 feet) for 30-70 seconds.
After diving, these birds spend long periods standing with wings outstretched to allow them to dry, since they are not fully waterproofed. They fly low over the water, with their bills tilted slightly upward. They sometimes leave their colony in long, single-file lines.
This species migrates from the coldest parts of its range, such as eastern Canada, and has occurred in Europe as a very rare vagrant, for example in Great Britain, Ireland and the Azores.
The Double-crested Cormorant's numbers decreased in the 1960s due to the effects of DDT. Colonies have also been persecuted from time to time in areas where they are thought to compete with human fishing.
Recovery
Recently the Double-crested Cormorant has greatly increased in abundance beyond what was known historically. It is believed that the recovery was allowed by the decrease of contaminants, particularly the discontinued use of DDT. It is believed that it has increased to such great numbers because of aquaculture ponds in its southern wintering grounds. The ponds favor good over-winter survival and growth.
Also, 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 implicated in the decline of some important sport-fish populations in the Great Lakes and other areas. Scientists are not in universal agreement about the exact extent of the role of cormorants in these declines, but the growing consensus is that Double-crested Cormorants are a real factor for some populations and in some locations.
In light of this, and because of calls for action by the public, the United States Fish and Wildlife Service (the US Federal government agency charged with their protection) has recently extended control options to some other government entities. This includes some lethal culling of populations and measures to thwart reproduction, all in an effort to control their growing numbers.
The U.S. Fish and Wildlife Service retains oversight and the control measures are not extended to the general public (no hunting season). Many government agencies at differnt levels in both the U.S. and Canada continue to wrestle with how best to respond to the situation.
Folk names of this bird include Crow-duck, Farallon Cormorant, Florida Cormorant, lawyer, shag, and Taunton turkey.
Phalacrocorax is Latinized Greek for phalakros (bald) and kora (raven); auritus is Latin for eared.
References
- Alsop, Fred J. III; Birds of Texas. Smithsonian Handbooks: DK Publishing, Inc., New York, NY (2002).
