Brood parasitism evolves from this situation to avoid fighting over the nest. Rarely fledge young other than that of the parasite, as the parasite young usually hatches first and grows faster. The parasite young may actually remove host eggs or kill host young. Egg mimicry undoubtedly arose in response to the host evolving egg-recognition abilities. This has undoubtedly evolved in response to species-specific recognition abilities in the host.
Cooperative breeding increases the survival of young of related birds.