The Smew (Mergellus albellus) is a small duck which is somewhat intermediate between the typical mergansers (Mergus) and the goldeneyes (Bucephala). It is the only member of the genus Mergellus; sometimes included in Mergus, this genus is well distinct (though closely related) and might actually be a bit closer to the goldeneyes. The Smew has interbred with the Common Goldeneye (B. clangula).
An unnamed fossil seaduck, known from a humerus found in the Middle Miocene Sajóvölgyi Formation (Late Badenian, 13-12 million years ago) of Mátraszőlős, Hungary, was assigned to Mergus. However, the authors included the Smew therein, and consequently, the bone is more properly assigned to Mergellus "? especially as it was more similar to a Smew's than to Bucephala remains also found at the site. It is sometimes argued that the Mátraszőlős fossil is too old to represent any of the modern seaduck genera, but apparently these were all well-distinct even back then.
The living species is known to exist since about 2 to 1.5 million years, as attested by fossils from the earliest Pleistocene found in England.
The drake Smew, with its 'cracked ice' appearance, is unmistakable, and looks very black-and-white in flight. The females and immature males are grey birds with chestnut foreheads and crowns, and can be confused at a distance with the Ruddy Duck; they are often known as "redhead" Smew. It has oval white wing-patches in flight. The Smew's bill has a hooked tip and serrated edges, which help it catch fish when it dives for them.
Distribution and ecology
a Smew taking off
This species breeds in the northern taiga of Europe and Asia. It needs trees for breeding. The Smew lives on fish-rich lakes and slow rivers. As a migrant it leaves its breeding areas and winters on sheltered coasts or inland lakes of the Baltic Sea, the Black Sea, northern Germany and the Low Countries, with small number reaching Great Britain (for example, at Dungeness), mostly at regular sites. On lakes it prefers areas around the edges, often under small trees.
The Smew breeds in May and lays 6-9 creme-colored eggs. It nests in tree holes, such as old woodpecker nests. It is a shy bird and flushes easily when disturbed.
The Smew is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies. It is not considered threatened by the IUCN.