When the female cuckoo thinks it is the right moment she will fly down to the reed warblers' nest, pushes one reed warbler egg out of the nest, lays her egg and flies off. This only takes about 10 seconds. The reed warbler does not notice, and carries on looking after the eggs. When the cuckoo chick hatches it soon grows very fast. It pushes the other eggs or reed warbler chicks out of the nest. At 14 days old, it is about 3 times the size of the adult reed warblers. The chick has a huge mouth which it opens very wide. It also makes a very fast “cheeping” sound which sounds like a nest full of reed warbler chicks. This makes the parents behave as if they had a nest full of their own chicks.