Mallards start to pair up in October and November, and start to nest in March.
They prefer to nest near water and the duck generally makes her nest well covered in vegetation or in a natural hole in a tree.
Mallards exploit any open water where food is plentiful, however, and this sometimes results in the choice of less than perfect nest sites, particularly in towns. Nests have been found in boathouses, wood piles, old crows nests, hay stacks, roof gardens, enclosed courtyards and even in large flowerpots on balconies several floors up!
Town ponds with an abundant and reliable food supply often attract more mallards than are able to nest close by. In such situations many ducks nest well away from the pond to avoid competition and harassment from others.
The female builds a nest from leaves and grasses and lines it with down plucked from her breast. Eggs are laid between mid-March and the end of July. The normal clutch is about 12 eggs, laid at one to two day intervals. After each egg is added, the clutch is covered to protect it from predators.
If you find a nestful of duck eggs, leave it well alone; it is unlikely to have been abandoned. The laying period is very stressful for the female as she lays more than half her body weight in eggs in a couple of weeks. She needs a lot of rest and depends heavily on her mate to protect her and their feeding and loafing areas.
The role of the male is almost over once the clutch is laid. He remains sexually potent for a while in case a replacement clutch is needed, but gradually loses interest and joins other males to moult. At this time groups of males with no obvious duties often mate forcibly with females that appear to be unattached. This anti-social phase is short-lived and ends once moulting is underway.