Those bastards wait till a mother bird from a different species has left the nest to get food. The Cuckoo will then sneak in a lay an egg in the other birds nest then disappear like John Wayne riding into the sun set.
A few weeks later the Cuckoo egg will hatch, usually before the other birds brood. The cuckoo chick, hours old, will then use a specifically designed hollow in its back to push the other eggs out of the nest, killing them off one by one. The bird then raises the Cuckoo as it’s own, never realising the deception.
When it’s old enough the Cuckoo will fledge and leave the nest. It never visits, writes or even remembers the birthday of its adoptive mother
Another thing that makes them dicks, the mother cuckoo doesn’t care how big the forced adoptive mother is. The Cuckoo chick is quiet often double the size of it’s fully grown adoptive parent!
tl;dr mother Cuckoo lays it’s eggs in another species nest. Baby Cuckoo then murders it’s adoptive brothers and sisters. Adoptive mother cares and raises the Cuckoo leaves home, never visits or phones.