Robin's nest with a brown-headed cowbird egg

© Edward Kinsman/Science Photo Librar

Freeloaders of the bird world

It’s not just cuckoos that sneak their eggs into the nests of other birds. Our homepage image features an uninvited speckly-white visitor to a robin's nest. That smaller egg belongs to a baby cowbird, whose mother laid it among the blue robin eggs when no one was looking. Once the baby birds all hatch, the cowbird will grow much faster and larger than its robin 'siblings’, outcompeting them for food. And if mama robin ejects the cowbird egg before it hatches, the cowbird mum might take notice and chuck the remaining robin eggs from the nest out of spite.