* The egg may have been infertile. Infertile eggs are not viable and will not hatch, so the mother mallard may break them to remove them from the nest.
* The egg may have been damaged by predators. Predators, such as raccoons, skunks, and crows, may break mallard eggs in order to eat the egg yolk or the developing chick.
* The egg may have been accidentally broken by the mother mallard. Mallard eggs are fragile and can easily be broken if they are stepped on or bumped by the mother mallard.
* The egg may have been broken by a sibling. Mallard ducklings are known to fight with each other for food and space in the nest, and this can sometimes result in eggs being broken.
In some cases, a broken mallard egg may be a sign of a larger problem, such as a predator infestation or a lack of nutrients in the mother mallard's diet. If you find a broken mallard egg in the nest, it is important to remove it as soon as possible to prevent it from attracting predators. You can also try to deter predators by placing a protective barrier around the nest, such as a chicken wire fence or a plastic net.