SmewMergellus albellusWhere and when to see them

The Smew is a small diving duck with strikingly different male and female plumages. A male’s white body and black facial pattern can stand out at considerable range, while a chestnut-headed female is easier to overlook. The Rhine registration concerns Augst–Whylen, the Ergolz mouth and nearby old-Rhine waters upstream of Basel, not the entire cruise river. Species reference: https://birds-europe.linnaeus.naturalis.nl/linnaeus_ng/app/views/species/nsr_taxon.php?id=130454

Size

38–44 cm (15–17 in) total length, Naturalis Birds of Europe.

Weight

Species-specific weight not verified.

Lifespan

Species-specific lifespan not verified.

Status

Formal global conservation category not verified.

Birds obtain food by diving and often bring prey back to the surface before swallowing. Naturalis describes daytime feeding and dives to several metres. A bird can disappear during a scan and surface well away from the original spot. Watch repeatedly rather than identifying a small group from a single moment.

• It is smaller than the larger sawbills.
• Males and females look very different.
• Females have chestnut-coloured heads.
• It feeds by surface-diving.
• Small fish are important winter prey.
• It nests in tree holes in its breeding range.

WWF Basel recommends October–March for winter waterbirds at Augster Stau, but that recommendation is not specific to Smew. The registry calls Smew chiefly a passage or winter visitor. Those qualitative statements are retained without turning the whole waterbird season into species-specific numerical months.

Breeding habitat includes wooded northern wetlands, where the species nests in tree holes. Nonbreeding birds mainly use freshwater. The impounded Rhine and protected bays near Augst–Whylen provide a relevant search landscape, but local waterbird concentrations are dominated by other ducks. Suitable water does not make an uncommon visitor likely on demand.

Small fish are especially important in winter and early spring, with aquatic insects also taken at other times. This is a general European species account, not a feeding study at Augst. Avoid assigning a locally preferred fish species or interpreting every dive as a successful capture; neither was verified.

Common name

Smew

Scientific name

Mergellus albellus

Animal group

Birds

Size

38–44 cm (15–17 in) total length, Naturalis Birds of Europe.

Weight

Species-specific weight not verified.

Lifespan

Species-specific lifespan not verified.

Status

Formal global conservation category not verified.

Identification

An adult male appears mainly white with a black eye patch and fine dark body markings. Females have a chestnut crown and nape, white cheek and throat, and grey body. Juveniles resemble females. The compact body and short bill help separate Smew from larger sawbills, but distant female-type ducks require care.