There are several species of birds in the family Mergus known as Mergansers. Unlike dabbling ducks, which have smooth broad bills for filtering out particles of food from water, these diving ducks have narrow beaks with saw-like edges, well suited to their diet of mainly fish.

Red-breasted Merganser

The Red-breasted Merganser (Mergus serrator), as its name suggests, has a red-brown breast. Males of the species have dark green heads with a white collar, and females have red-brown heads. Their beaks are red. They are widespread in the Northern Hemisphere, with populations in North America, Europe and Asia. They are classed as Least Concern by the International Union for Conservation of Nature (IUCN). They spend the winter in the southern parts of their range, often being seen in the sea. They migrate to the north for the breeding season and make their nests among bushes or rocks on the ground near lakes. Females incubate up to 11 eggs for a month (the males take no role in caring for the eggs or chicks). The chicks can feed themselves when they hatch. The mother may take care of them, but they are often looked after by a non-breeding female 'auntie' until they are fully grown at about two months old.

Goosander

The Goosander (Mergus merganser) is also widespread around the Northern Hemisphere from North America to Asia. They are also classed as Least Concern by the International Union for Conservation of Nature (IUCN). Similar to Red-breasted Mergansers, females have a red-brown head and males have dark green heads, but the males lack the white collar and red-brown breast of their cousins. They nest in crevices in trees, rocks or even buildings, and are mostly to be found in freshwater areas. Some breed in colder areas, such as Canada and northern Russia, and migrate substantial distances south for the winter, while others breed in warmer areas, such as Afghanistan, and migrate shorter distances to their winter feeding grounds. Like Red-breasted Mergansers, females lay up to 11 eggs and incubate them without the males. However, the mothers (rather than aunties) look after the chicks until they are fully grown, often in groups with more than one family. Like grebes, the chicks sometimes ride around on their parent's back.

Scaly-sided Merganser

The Scaly-sided Merganser (Mergus squamatus) is classed as Endangered, as these birds are only found in a small area in South East Asia. These birds are similar in plumage to their cousins, with males having dark heads and females red-brown heads, but they have patterns in their plumage that makes it look like their sides are covered in fish scales. They nest in tree crevices, mainly in south east Russia, and migrate south to parts of China, Japan, Myanmar or the Korean peninsula for the winter.

Brazilian Merganser

The Brazilian Merganser is classed as Critically Endangered, as there are thought to be fewer than 250 birds left in the wild, and they are mainly found in a small area of Brazil. Their plumage is darker than that of their cousins, being grey-black. Males and females have dark heads. They nest in crevices in trees or rocks, and stay close to their breeding sites throughout the year, rather than migrating.

New Zealand Merganser

The New Zealand Merganser (Mergus australis) was discovered in 1840. However, it was hunted to extinction - the last recorded sighting was in 1902 and it was confirmed as extinct in 1988.

Other Species

The Smew (Mergellus albellus) is related to birds in the Mergus genus. It is classified as Least Concern but its population is decreasing. Males of this species develop bright white plumage with black eye patches. The females have red heads. They are found in parts of Europe and Asia, and also Alaska.

The Hooded Merganser (Lophodytes cucullatus) has a sawbill, and is named for the hood-like plumage on its head - the females are brown, while the males are mostly-black birds with white hoods. They can be found in North America.