Common goldeneye

Bucephala clangula

Brilduiker / Schellente / Garrot à oeil d'or

The common goldeneye is a medium-sized sea duck of the genus Bucephala, the goldeneyes. Their closest relative is the similar Barrow's goldeneye.

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 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. They will readily use nestboxes, and this has enabled a healthy breeding population to establish in Scotland where they are increasing and slowly spreading with the help of nestboxes. They are usually quite common in winter around lakes of Britain and some are being encouraged to nest in nestboxes which are put up to try to have them there all year round. Occasionally recorded as a vagrant in various parts of the Indian Subcontinent.

Often the natural tree cavities are made by broken limbs, unless they are made by pileated woodpeckers or black woodpeckers, the only tree-cavity-making animals who make a cavity large enough to normally accommodate a goldeneye. Average egg size is a breadth of 43.3 mm (1.70 in), a length of 59.3 mm (2.33 in) and a weight of 64 g (2.3 oz). 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 both with other common goldeneyes as well as with other duck species, and even tree swallow and European starling eggs have been found mixed with goldeneye eggs. The broods commonly start to mix with other females' broods as they become more independent. 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.

These diving birds 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 (Ursus spp.), various weasels (Mustela spp.), mink (Mustela vison), raccoons (Procyon lotor) and even Northern Flickers (Colaptes auratus) and red squirrels (Tamiasciurus husonicus).

This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be stable, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern (IUCN, 2012).

The global population is estimated to number c.2,500,000-4,600,000 individuals (Wetlands International 2006), while national population estimates include: <c.100 breeding pairs and c.50-1,000 wintering individuals in China; c.1,000 wintering individuals in Japan and c.100,000-1 million breeding pairs and c.10,000 wintering individuals in Russia (Brazil 2009).

The species is threatened by wetland degradation and loss in North America and is susceptible to atmospheric acid deposition (e.g. acid rain) throughout a large part of its breeding range (Kear 2005b). The main threat to the species in its wintering range is pollution (e.g. from coastal oil spills or other pollutants from sewage outfalls) (del Hoyo et al. 1992). The species is hunted sustainably in Denmark (Bregnballe et al.2006) although the influence of hunting on global populations is unknown (Kear 2005b).

Above: Common goldeneyes, adult pair (drake right, female left).

Above: Common goldeneye, adult drake

Above: Common goldeneye, adult drake in eclipse moult

Above: Common goldeneyes, three adult drakes