Diving ducks as part of their adaptation to a more aquatic lifestyle have their legs set further back on their bodies than dabbling ducks. This gives them more manoeuvrability on water but makes them ungainly on land, and as a result when nesting they often prefer to build their nests at the edge of the water, often in reeds or other dense vegetation. The usual clutch is 6-8 eggs. When they hatch, the ducklings immediately enter the water and will dive deep from a few hours old. This means if rearing them away from the parents they need a deep tank, otherwise they are liable to bang their heads on the bottom if startled!
A small duckling is a tasty meal for large predatory fish, and the introduction of tilapia to Lake Alaotra, combined with habitat loss, is probably the cause of the near-extinction of the Madagacar Pochard. Even other species experience high losses during the fledging period.
(images from Wikipedia)