>>718064685
Depending on the species cuckoos won't lay their eggs in their own nest and raise their chicks, they'll lay their eggs in OTHER birds' nests and those other species will raise the cuckoo chicks instead. Cuckoo eggs will hatch earlier than their host nest's species, then push the other eggs out of the nest so the parent has no choice but to raise the cuckoo chick.
Natural selection favors adaptation though, so host species and cuckoo species will favor adaptations that either increases their chance of making the parasitic eggs fuck off/getting eggs in host nests, respectively. One adaptation is chicks being born with blue markings on their beaks, which help the parent identify their own chicks. Another adaptation is cuckoos laying eggs that closely resemble that of the host species, some cuckoos lay pitch black eggs to hide the eggs from the host, who can't see them. Sometimes cuckoos will destroy the other host eggs if the host destroys the parasitic cuckoo egg, thus hosts will raise the cuckoo chick anyway because removing it isn't worth the death of the rest of the clutch. And so on.
Cuckoos are the most well-known parasitic birds.
