The cuckoo don't take care of its sons. It reproduces itself  using the nest of others birds , like for example, here, the nest of the blackcap. The following pictures try to tell something about that. Click on thumbnails to view full-size artwork.

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Left to the right:
1. The female cuckoo takes off an egg from the nest of the blackcap.
2. Next it puts an its own egg in the removed one place.
3. After that, it goes away and seeks others nests to repeat the operation.
4. Without to perceive what has happened, the blackcap comeback to its nest to hatch the eggs.
5. The cuckoo is the first to be born and just after this takes off the  eggs of the blackcap to be free from competitors.
6. The blackcap is feeding the young cuckoo that, meanwhile, exceed its stepmother several times in size.
7. In August, the young cuckoo is ready to undertake  its long journey to the African Tropical regions. In the next   Spring, it will be back at the place in which it was born.

In the next page you can see some Portuguese popular believes about cuckoo