Common cuckoo

The common cuckoo begins to lay eggs in early July.

An excerpt from the article 20 facts about Common cuckoo
During this time it is able to produce and lay 10 to 20 eggs. There are usually two days between egg-laying. The eggs are very similar to those of the species on which they parasitize. This type of resemblance is called mimicry and is intended to increase the chances that the egg cast will survive and hatch.