Newly hatched ducklings feed almost exclusively on invertebrates. This includes everything from earthworms to small crustaceans, snails, and insect larvae and adults.
Invertebrates provide a concentrated source of protein and fat required by a rapidly growing animal.
By the time ducklings are about 2 weeks old, or one-quarter grown, they begin to consume a diet that is more adult like. Invertebrate availability influences where a hen will take her brood. Very often people find a mallard nest close to a particular wetland and then are concerned because the eggs hatched, but the brood never appeared on their wetland. Many folks think that this means that something killed the ducklings, but in many cases it simply means that the hen took the brood to another wetland that had richer invertebrate resources. Such wetlands may be as far as 3 miles away from the nest.