Why does egg mimicry increase the chance that a cuckoo egg will be accepted?

Egg mimicry significantly increases the chances of a cuckoo egg being accepted because many host species have evolved the ability to discriminate between their own eggs and foreign ones. When a host bird perceives a foreign egg in its nest, it often reacts by abandoning the nest, building over the existing clutch, or ejecting the strange egg.123

By producing eggs that closely resemble those of the host in color and pattern, the cuckoo reduces the likelihood of detection and rejection. Research indicates that this adaptation is highly effective: one survey found that only about 5 percent of well-matched eggs were rejected by hosts, whereas up to 72 percent of mismatched eggs were removed or caused the host to abandon the nest. Consequently, cuckoos that successfully mimic host eggs are more likely to have their offspring reared by foster parents, providing a clear evolutionary advantage.231