Smew

Mergellus albellus

Nonnetje / Zwergsäger / Harle piette

The smew is a species of duck, and is the only member of the genus Mergellus. This genus is closely related to Mergus and is sometimes included in it, though it might be closer to the goldeneyes (Bucephala). The smew has interbred with the common goldeneye (B. clangula).

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 theLow Countries, with a small number reaching Great Britain (for example, at Dungeness), mostly at regular sites. Vagrants have been recorded in North America. On lakes it prefers areas around the edges, often under small trees. The smew breeds in May and lays 6–9 cream-colored eggs. It nests in tree holes, such as old woodpecker nests. It is a shy bird and flushes easily when disturbed.

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). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very 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.130,000 individuals (Wetlands International 2006), while the population in Korea has been estimated at c.50-10,000 wintering individuals (Brazil 2009). 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 on the IUCN Red List, though its population is decreasing.

Where it occurs in large numbers on coastal waters the species is particularly vulnerable to oil pollution (del Hoyo et al. 1992). Populations declined in Europe throughout the 19th and 20th centuries due to habitat degradation and loss (e.g. the loss of mature trees in river valleys as a result of logging, conversion to agriculture and river canalisation) (Kear 2005b). The species has also suffered local declines as a result of predation by American mink Neovison vison (Kear 2005b), and is susceptible to avian influenza so may be threatened by future outbreaks of the virus (Melville and Shortridge 2006). The species is susceptible to a certain amount of hunting pressure when on passage and during the winter (del Hoyo et al. 1992).

Above: adult drake Smew

Above: adult female Smew

Above: adult drake Smew

Above: adult drake Smew

Above: adult female Smew

Above: adult female Smew

Above: adult female Smew

Above: adult Smew, drake in eclipse plumage