The Smew (Mergellus albellus) is a small, distinctive species of diving duck known for the male’s striking black-and-white plumage. It belongs to the Merginae subfamily, commonly referred to as sea ducks, which includes mergansers and goldeneyes. The Smew is the sole living member of its genus, Mergellus, though it is closely related to the larger mergansers. It is a highly migratory species, traveling between its northern breeding grounds and temperate wintering habitats.
Physical Description and Classification
The Smew exhibits pronounced sexual dimorphism, meaning the male and female have distinctly different appearances. The adult male, or drake, is often described as having a “cracked ice” or “panda” look due to its dazzling white body contrasted with bold black markings. These black features include a patch around the eye and a distinctive black line running down the back of the white, slightly bushy crest on its head.
The female, sometimes called a “redhead,” is significantly less conspicuous, featuring a primarily grey body with a contrasting rusty-brown crown and nape. She has a white patch on her cheeks and a black patch around the eye, but her coloration provides better camouflage than the male’s bright plumage. Both sexes share a slender, hooked bill with serrated edges, a feature common among fish-eating ducks that aids in gripping slippery prey. The Smew is a petite diving duck, measuring between 15 and 17 inches long and weighing typically 16 to 23 ounces.
Global Range and Migration Patterns
The Smew is a full migrant across Eurasia, breeding deep within the northern taiga forests. These breeding grounds stretch from northern Scandinavia eastward across Russia to eastern Siberia, where the birds favor clear, slow-moving rivers and forested lakes. They are obligate cavity nesters, relying on tree holes, often those previously used by woodpeckers, for reproduction.
Following the breeding season, Smews undertake significant migrations to reach their wintering grounds, leaving their northern territories between September and early October. The non-breeding range extends to temperate regions across Europe and Asia, including the Baltic Sea, the Black Sea region, Central and Western Europe, the Caspian Sea, and East Asia.
Arrival in wintering areas can occur from December to January, often prompted by freezing conditions further east. They favor large, open bodies of water during winter, such as ice-free freshwater lakes, reservoirs, sheltered coastal waters, and estuaries. Spring return migration commences in March, with the ducks arriving back at their northern breeding sites by April or May.
Feeding Habits and Behavior
As a specialist diving duck, the Smew primarily forages by diving from the water’s surface to pursue prey underwater. They are powerful swimmers, using their legs and wings for propulsion while actively pursuing food. Their diet is varied, shifting seasonally depending on prey availability.
During winter, their diet consists mainly of small fish, which they efficiently catch using their specialized bills. In summer and during the breeding season, they shift their focus to aquatic invertebrates, including insect larvae, crustaceans, and small amphibians. The Smew’s preferred feeding habitats are clear, slow-moving waters, as visual cues are important for locating and capturing prey.
The species is quite shy and cautious, flushing easily when disturbed by human activity. While they are mostly silent outside of the breeding season, males perform distinctive courtship displays in late winter. These displays include an upward stretching of the head and raising of the crest, often accompanied by a rattling, click-like call to attract a mate.
Conservation Status
The Smew is currently classified as Least Concern on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. Although not globally threatened, its population is suspected to be slowly decreasing. The global population is estimated to be over 130,000 individuals.
Local populations face vulnerability due to various localized threats across their vast range. Habitat loss and degradation are significant concerns, particularly the draining of wetlands and the loss of suitable nesting sites in tree cavities. The species is also susceptible to oil pollution in coastal wintering areas and the impacts of climate change.