The common goldeneye is a medium-sized sea duck of the genus Bucephala, the goldeneyes. Its closest relative is the similar Barrow's goldeneye. The genus name is derived from the Ancient Greekboukephalos, a reference to the bulbous head shape of the bufflehead. The species name is derived from the Latinclangere. Common goldeneyes are aggressive and territorial ducks, and have elaborate courtship displays.
Description
Adult males ranges from and weigh approximately, while females range from and weigh approximately. The species is named for its golden-yellow eye. Adult males have a dark head with a greenish gloss and a circularwhite patch below the eye, a dark back and a white neck and belly. Adult females have a brown head and a mostly grey body. Their legs and feet are orange-yellow.
Habitat and breeding
Their breeding habitat is the taiga. They are found in the lakes and rivers of boreal forests across Canada and the northern United States, Scandinavia, the Baltic States, and northern Russia. They are migratory and most winter in protected coastal waters or open inland waters at more temperate latitudes. Naturally, they nest in cavities in large trees, where they return year after year, though they will readily use nest boxes as well. Natural tree cavities chosen for nest sites include those made by broken limbs and those made by large woodpeckers, specifically pileated woodpeckers or black woodpeckers. Average egg size is a breadth of, a length of and a weight of. The incubation period ranges from 28 to 32 days. The female does all the incubating and is abandoned by the male about 1 to 2 weeks into incubation. The young remain in the nest for about 24–36 hours. Brood parasitism is quite common with other common goldeneyes, and occurs less frequently with other duck species. The broods commonly start to mix with other females' broods as they become more independent or are abandoned by their mothers. Goldeneye young have been known to be competitively killed by other goldeneye mothers, common loons and red-necked grebes. The young are capable of flight at 55–65 days of age.
Diet
Common goldeneyes are diving birds that forage underwater. Year-round, about 32% of their prey is crustaceans, 28% is aquatic insects and 10% is molluscs. Insects are the predominant prey while nesting and crustaceans are the predominant prey during migration and winter. Locally, fish eggs and aquatic plants can be important foods. They themselves may fall prey to various hawks, owls and eagles, while females and their broods have been preyed upon by bears, various weasels, mink, raccoons and even northern flickers and red squirrels.
Conservation
The common goldeneye is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds applies. Approximately 188,300 common goldeneyes were killed annually by duck hunters in North America during the 1970s, representing slightly less than 4% of the total waterfowl killed in Canada during that period, and less than 1% of the total waterfowl killed in the US. Both the breeding and winter habitat of these birds has been degraded by clearance and pollution. However, the common goldeneye in North America is known to derive short-term benefits from lake acidification.
