A house finch has built a nest and laid eggs in one of my hanging flower baskets. I noticed that there are a total of four eggs in the nest, three similar looking and one slightly larger different colored egg. Why is there an odd looking egg in the nest?
It sounds like a brown headed cowbird has laid an egg in the nest. Cowbirds are considered a parasitic species because they do not build their own nest. Instead they lay their eggs in the nests of other birds and rely on them to hatch and raise their young. A cowbird will lay one egg in a nest and knock one of the other eggs out of the nest. Some birds like the house finch, will accept the egg and raise the young cowbird as one of its own. However, some host birds will kick the cowbird egg out of the nest, desert the nest, or build a new nest over the cowbird egg.