Mergus

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Mergus is a genus of typical mergansers, a group of fish‑eating ducks in the subfamily Anatinae. The name Mergus is Latin and was used by ancient writers for an unspecified waterbird.

Living and extinct species
- Common merganser (Mergus merganser)
- Red-breasted merganser (Mergus serrator)
- Scaly-sided merganser (Mergus squamatus)
- Brazilian merganser (Mergus octosetaceus)

Extinct or recently extinct:
- Auckland Island merganser (Mergus australis)
- Chatham merganser (Mergus milleneri)

Related birds
- Hooded merganser (Lophodytes cucullatus) is closely related but not in this genus.
- Smew (Mergellus albellus) is more closely related to goldeneyes and is in a different genus.

Habitat and feeding
- Although they are seaducks, most mergansers prefer rivers and lakes; the red-breasted merganser is the one often seen at sea.
- They are large, fish-eating ducks with black-and-white, brown, or green plumage and often have a shaggy crest.
- Their long, thin bills have serrated edges to grip slippery prey. Because of these saw-like bills, they are sometimes called sawbills (along with the hooded merganser and the smew).

Diving and classification
- Mergus ducks are classified as diving ducks because they dive to find food.
- Among Anseriformes, the genera Mergus, Lophodytes, Mergellus, and Bucephala are similar and share a unique feature: they do not have notches at the hind edge of the sternum, but holes surrounded by bone.
- The genus Mergus was created by Carl Linnaeus in 1758. The type species is Mergus serrator (designated in 1838).

Fossils
- Some fossil birds were once thought to be mergansers, but their exact relationships are still studied.