Classify the behaviors of animals in our culture, and adjectives are attributed to the cuckoo are unflattering: operator, cheater, liar, fraud, etc ... But like I said, are just classifications of our moral system to a survival tactic, which, however, is as valid as any other.
What causes this animosity towards the cuckoo is taking advantage of other poultry farms, deceives and makes slaves. What happens is that when the cuckoo bird detects that a (usually
small, insectivorous bird) is laying eggs, the cuckoo deposits in the nest egg with these. The Cuckoo's Egg will be just the same, very similar in color, size and shape to host bird's eggs (above). Sometimes they are so alike that even the most expert ornithologists know the difference.
Then, as all eggs are equal, the host birds, hatch and care for the state of the egg that is not theirs, but the cuckoo.
But the Cuckoo's plan does not stop there, once the eggs hatch (usually the cuckoo is first) the cuckoo chick to not even get rid of all the other eggs, either pushing them to throw the nest or until just pecking with them. In this way ensures that the food brought by parents, guests birds, is just for him. Deceived, birds fed the only guest who is not her son but the cuckoo, and is also the murderer of the dead children.
In the top right image we can see the cuckoo, much larger than their adoptive parents, still fed by them.
Watch this video You'll be amazed to see how it works the cuckoo.