Many birds have reason to worry that the eggs in their nest might not be their own: birds often deposit eggs into other nests and it is not easy for parents to tell their eggs from others. Researchers at the University of Veterinary Medicine, Vienna have discovered that tree sparrows can recognise eggs deposited by other tree sparrows but do not always reject them. The results are published in the online journal Plos One.
Building a nest, laying and incubating eggs and taking care of a hungry brood are very demanding on birds´ energy budgets, so it is obviously in their interests to ensure that the young they are caring for are their own. Brood parasitism sometimes makes this a difficult proposition: strangers – either of their own kind or of another species – might want a free ride and deposit their eggs into ready-made nests.