Black-headed gulls have an interesting parenting strategy; they remove eggshells from their nests to protect their chicks from predators. Even though the shells are hard to spot, predators can still find them quickly. Therefore, the farther away the shells are, the safer their babies are.
In one experiment, eggs near shells were three times more likely to be taken by predators, so it is important for the parents to precisely time when they take out the trash.
The parents must also be careful to leave the nest when the chick has fluffed up a bit, as some of their baby’s predators are other black-headed gulls and leaving too early can mean death by cannibalism.