Ducklings grow rapidly. In just a couple of months, an egg becomes a bird with feathers that enable flying thousands of kilometres. Growing feathers requires a lot of protein. Where do ducklings get the protein?
If you have ever visited a wetland, you may have noticed a lot of invertebrates, for example mosquitoes and dragonflies. Many invertebrates flying around the wetlands actually lay their eggs in water. The larvae will develop in the water and emerge when ready to fly. Often these flying invertebrates rest on wetland vegetation. Swimming and flying invertebrates are duck food.
Wetlands are occupied by many kinds of aquatic invertebrates from small zooplankton to large beetles. They are all duck food, but ducks also help them disperse from one pond to another: invertebrates and their propagules can be carried over long distances in duck feathers or intestines.
What type of food a duck consumes depends on the duck species. Ducks are specialised to eat various types of nutrition, and for example the size of the lamellar (teeth like structures used for filtering or straining food) in the bills differs between species. Diving and dabbling ducks have diverging ways of reaching their food. Diving ducks, even their small ducklings, dive under water and can utilise swimming and benthic aquatic invertebrates.
Females should find good foraging spots for their broods. Broods can move long distances from the nesting site to find proper food patches. Most European ducks breed in the boreal zone, but many lakes lack enough invertebrate food for ducklings. Thus many of the lakes are empty of duck broods.
The common goldeneye (Bucephala clangula), a diving duck, is associated with boreal lakes with large numbers of free-swimming aquatic invertebrates (e.g. dytiscidae) and large emerging invertebrates (caddisflies and mayflies). Of these, mayfly larva live in the bottom of the wetlands.
Of the dabbling ducks, the mallard (Anas platyrhynchos), common teal (A. crecca) and Eurasian wigeon (Mareca penelope) are sympatric species with a shared niche. However, the habitat use of their broods differ. While mallard broods prefer lakes with luxuriant vegetation and large emerging invertebrates, teal broods utilise lakes with smaller emerging invertebrates, such as flies (diptera). Flies are abundant especially in newly created wetlands and flowages, and teals are considered pioneering species.
Adult wigeons are vegetarians, and also appear to prefer lakes with luxuriant vegetation during the brood stage, but small flies are also important for them. Beavers are important for mallards and wigeons in the boreal landscape: lakes that typically lack luxuriant vegetation can establish large and shallow well-vegetated areas during the beaver flood. Thus beavers can provide habitat enhancement. Without them less lakes would be available in the boreal landscape for wigeons and mallards.