Double-Crested Cormorant (Nannopterum auritum)
By Niyati Acharya
The Double-crested Cormorant is a large, black waterbird common to lakes and shorelines throughout North America. Though an expert fisher, its feathers lack the waterproofing common to most other waterbirds. They spend considerable time drying their feathers and can be seen with their waterlogged wings spread out to dry in the sun.
The Cormorant is an efficient fish hunter. Its heavy bones and lack of buoyancy enable it to dive more easily and remain underwater for a considerable amount of time, while pursuing prey.
The Cormorant’s distinctive features are its black, long neck and long, hooked, orange bill. The birds are roughly the size of a small goose and have strong, webbed feet. Unlike geese and ducks; however, the Cormorant’s webbed feet show a totipalmate arrangement, meaning that all four toes are connected by webbing.
The species is generally silent, but gives deep, croaking calls at its breeding colonies and roosts. They gather, year-long, in congregations that can number in the thousands. They prefer small islands and can be spotted alongside other colonial-nesting bird species, such as the Great Blue Heron, Great Egret, Black-crowned Night Heron, and Royal Tern.
The history of conflict between Double-Crested Cormorants and human interest in fisheries is long. Overall, Double-Crested Cormorants are not major consumers of commercial and sportfish species. They often congregate and can have significant local impacts where high concentrations of fish occur, such as stocking release sites, private fishing ponds, aquaculture ponds, reservoirs, spawning sites, and other areas.
In human-altered ecosystems where alternative habitat is limited, cormorants can affect the persistence of plant communities and other wildlife species that rely on these habitats.
The species is a migratory piscivorous bird with bicoastal and inland distributions in North America. Coastal breeding populations extend from Alaska to Mexico and from Newfoundland to Cuba.
The extent of the historical range and numbers of this species is poorly known, in part because frequent persecution by humans makes the baseline difficult to establish. Increases of numbers during the 20th century were interrupted throughout the range from about 1950-1970 in association with adverse impacts of bioaccumulated pesticides (Hatch and Weseloh 1999). Since the early 1970s, however, cormorants have increased widely, and it is likely that continental numbers have reached an all-time high.
Sources include:
American Bird Conservancy, U.S. Department of Agriculture, AmercianOrinthology.org,
Photo credit: Hagerty, Ryan/USFWS, Lovell, Charles D., USFWS, Alligator River NWR/USFWS
