Is cuckoo and example of onomatopoeia?

No. Cuckoo is not an example of onomatopoeia. Onomatopoeia is a word that imitates the natural sounds of a thing. For example, the words 'hiss' and 'buzz' are examples of onomatopoeia. Cuckoo is not an onomatopoetic word because it does not imitate the sound of anything.