There are over 130 species of duck worldwide, which can be found in almost every environment where there is water. Ducks belong to the waterfowl family, Anatidae, which also includes geese and swans and they can broadly be divided into two groups; dabbling ducks and diving ducks.
They are further divided into smaller groups called tribes. Members of each tribe show similar characteristics or are closely related although there is much debate about the validity of some of the tribes and which ducks should sit where.
Dabbling ducks (Anatini)
Dabbling ducks, also known as surface-feeding ducks, puddle ducks, or dipping ducks, are ducks that feed either by grazing on land, or by upending on the surface of water without completely submerging.
Dabbling ducks have broad, flat bills with a comb-like structure along the sides called a pecten, which is used as a strainer to filter water out of the beak while trapping food. The pecten is also used for preening.
During breeding season dabbling ducks eat mainly aquatic invertebrates such as insects, crustaceans, molluscs, and worms. Out of breeding season they switch to a diet of aquatic plants as well as grains and seeds found on land and will often feed at night.
Dabbling ducks are lightweight and buoyant and they float high on the water. Their legs are placed towards the centre of their bodies which helps them tip up easily and stay afloat by paddling while keeping their bodies partially submerged. Their feet are relatively small, and the hind toe is not lobed because they do not need them for propulsion as they rarely dive. This arrangement combined with the position of their legs means they are able to walk well on land.
Dabbling ducks spend much of their time on shallow wetlands and marshes where they are vulnerable to predators. They have evolved long, broad wings compared to their body weight which enables them to take off vertically and quickly from water and to navigate elegantly around trees and other obstacles. This low wing loading means they can also land with pinpoint accuracy.
Dabbling ducks are most common in the temperate regions of the Northern hemisphere and are highly migratory. They are gregarious birds and will often live in flocks of mixed-species.
Examples of dabbling ducks
Diving ducks (Aythyini)
Diving ducks, also called pochards or scaups, feed by diving below the surface of the water, sometimes to depths of 20m. They either chase prey through the water or pick it from the river or seabed. They dive in by expelling air to reduced buoyancy, arching their body, and propelling themselves forward with their relatively large feet. Once they are underwater they use their legs together for sculling and in some species the wings are opened and used to steer rather than for propulsion.
A typical dive lasts between 10 and 30 seconds but diving ducks are capable of holding their breath for up to a minute which allows them time to descend, forage and feed, and return to the surface for air.
Diving ducks are heavier than dabbling ducks. Their bodies are wider in the middle and their wings are short and more compact so they can be pressed against their sides. They have larger feet with lobed hind toes, which are placed further back on the body. Although this gives them greater thrust underwater it means they are fairly ungainly on land.
While they are underwater, their heart rate slows which reduces the need for oxygen and although they use energy to push themselves underwater once they have finished feeding they simply relax their muscles and float back to the surface usually in the same place that they entered.
Diving ducks are unable to take off vertically because of their short wings. They use the surface of the water as a runway, beating their wings hard as they gain enough speed to enable them to take off. They land in a similar manner skidding across the surface of the water until they come to a stop.
Diving ducks live on expanses of open water on lakes and estuaries. They are mostly found in the Northern hemisphere and like dabbling ducks will often form mixed flocks.
Examples of diving ducks
Sea ducks (Mergini)
Sea ducks are some of the most colourful species of duck. They are typically marine birds that are found in coastal habitats, although they will venture inland during migration and breeding season.
They have evolved well for life at sea and are able to survive in extremely low temperatures. They have thick, fluffy down that provides superior thermal insulation and the veins and arteries in their legs warm cold blood before it returns to the body.
High quantities of salt would kill most birds, but sea ducks have a pair of glands above the eye that function like an extra kidney, drawing salt ions out of the bloodstream to be excreted via the nasal passages. This allows sea ducks to drink salt water without dying of thirst. Young birds take time to develop the ability to tolerate salt water which is why many species of sea duck lay their eggs and bring up their chicks away from the sea.
Sea ducks can dive to depths of 50 metres and have highly specialised bills. Eiders, for example, have heavy stout bills that enable them to feed on mussels and other bivalves, whereas mergansers have long, narrow, serrated bills that they use for catching and eating fish. Somewhat confusingly, most mergansers, otherwise known as sawbills, live in river habitats. It is only the red-breasted merganser that is common at sea.
Sea ducks don’t breed until they are 2 or 3 years old and tend to return to the same breeding areas year after year. If food is scarce they may skip a year. Sea ducklings on open water are vulnerable to predators and survival rates are fairly low. All this means many of the populations of seabirds are in decline due in part to habitat loss and contamination from oil spills and shipping.
Eiders are sometimes placed in a separate tribe called Somateriini.
Examples of sea ducks
Shelducks are an intermediate between geese and dabbling ducks and sit in a tribe together with the sheldgeese. The name derives from an Old English word for ‘pied’ and refers to the two-tone colouration found in most species. Until the 19th century they were known as sheldrakes and in North America this term is sometimes used for the canvasback which is not a shelduck but part of the diving duck tribe.
Shelducks and sheldgeese are large species of duck but smaller than true geese. They have short bills, long legs, and an upright stance. They have a distinctive wing pattern with white coverts and iridescent patches on their secondaries or greater coverts. Males have a bony knob on the bill which is responsible for the whistling sounds they make during courtship and aggressive displays.
They are found mainly in the Southern hemisphere; only the common shelduck and ruddy shelduck breed in northern regions.
Shelducks are mostly aquatic birds and feed by digging in mud as well as up-ending and dabbling in shallow water. They are ominvores and eat a varied diet of plant matter and aquatic insects and crustaceans. Sheldgeese spend much more time on land and are mostly vegetarian. Some species regularly spend their time perching in trees.
Shelducks are sociable birds and will often breed in colonies even looking for suitable nest sites together in small groups. They form long-lasting pair-bonds and produce large broods. After the young are hatched, they will leave them in creches with ducklings from other families with just one or two adults to care for them.
Examples of shelducks
Perching ducks (Cairinini)
Perching ducks are arboreal, and are mainly found by woodland lakes and rivers. They nest in cavities in hollow tree trunks often high above the ground, and have long claws on their toes which enable them to spend much of their time perched in trees. They have evolved short, broad wings which allows them to be highly manoeuvrable and are able to fly at speed through thickly wooded areas.
Perching ducks exhibit many similar behaviours to dabbling ducks, such as feeding habits and courtship behaviour. They also share some similar traits with shelducks such as wing pattern and many perching ducks are more closely related to species in other tribes than with each other.
Perching ducks, in particular the Mandarin duck and the wood duck, are commonly kept as ornamental waterfowl. The smallest ducks in the world, the pygmy geese, are members of the perching duck tribe.
Example of a perching duck
Stiff-tailed ducks are small, round freshwater diving ducks with long, pointed tail feathers which are erect when the duck is at rest. They use their tail feathers to steer underwater when foraging for food. Their legs are set far back on the body and they have small wings which makes it difficult for them to fly and get around on land so they spend most of their time on water including when sleeping.
Males tend to have reddish plumage and a broad, scoop-shaped, bright blue bill with a specialised tongue that allows water to be sucked in front of the bill. Hens are much plainer and often have lines on the front of the face.
Drakes have an air sac in the neck which is inflated during courtship rituals. They drum it with their bills to create a dull thudding sound, while erecting the crest on their head. Unusually for ducks, the male plays a part in rearing young.
Stiff-tailed ducks are mostly found in warmer parts of the world. They don’t migrate long distances but will make short journeys in response to different water conditions.