The common goldeneye (Bucephala clangula) is a medium-sized duck with large heads. It is a sea duck of the genus Bucephala, the goldeneyes. Common goldeneyes breed throughout Canada, Minnesota, Michigan, Alaska, and the northeastern United States of America. Among Canadian Boreal Forest lakes, they are most abundant, especially where lakes or deep marshes have substantial populations of invertebrates. The genus name comes from the traditional Greek boukephalos (“bullheaded”, from bous, “bull” and kephale, “head”), respect to the bulbous head shape of the bufflehead. The species name springs from the Latin clangere (“to resound”). The male Common Goldeneye contains a dark iridescent-green head that appears black when not within the sun. He also contains a prominent round or oval white spot on all sides of his face at the bottom of his black bill. His belly and flanks are white, and his rump is black. His back is usually white with black bars. the feminine Common Goldeneye incorporates a gray body, brown head, and yellow eyes. It can be very difficult to differentiate this bird from a Goldeneye of a female Barrow. The Traditional Goldeneye bill is typically black with a yellow tip, while the Barrow ‘s bill is mostly yellow. Juveniles are white with brownish eyes, similar to females but with less head and body-color distinction. Consult a guidebook or an experienced observer, consider range and habitat, and study nearby males for clues about which female and juvenile goldeneyes could be present. An adult male ranges from 45–51 cm (18–20 in) and weighs approximately 1,000 g (2.2 lb), while females range from 40–50 cm (16–20 in) and weigh approximately 800 g (1.8 lb).
Classic goldeneyes are cavity nesters and have a clear propensity toward homing, sometimes using the same cavity over successive years. Nests are typically situated near a pond, lake, or river, but can be found up to a mile from the water in woodlands. In natural tree cavities, female common goldeneyes nest in abandoned woodpecker holes or nest boxes and lay an average of 9 eggs. 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. They feed in large part on crustaceans, mollusks, small fishes, and some plant material along the coastal wintering grounds. They are fast fliers; in flight, their wings make a distinctive whistling sound. Males frequently display when females are nearby by stretching the head back against their back and then popping their heads forward. They spend winters mainly in protected coastal waters as well as on large lakes and rivers inside the country. Nonetheless, in North America, the common goldeneye is considered to reap short-term benefits from Lake Acidification.