within two days of hatching, leaving the cuckoo the sole chick. As newly hatched cuckoo chicks eject host eggs they do not get to learn the host's begging call, but can possess begging call polymorphism, where nestlings produce the calls of their primary host. As the nestling grows it will be fed by the host parent and possibly the group, growing more rapidly until fledged. Coevolutionary arms race Counter-adaptations have been documented for host species and cuckoos alike, as each adapts to the other in a coevolutionary "arms race". Studies show that coevolutions happen at all stages of the growth cycle, not just the early stages. Fairy-wrens have adapted some host defences to reduce parasitism. The high cost of hosting a parasitic species, in energy and genetics, drives the host to improve its defences, which in turn drive the parasite to improve its offences. Among the host's defensive adaptations: Hosts like to nest in large colonies, to cooperate in spotting cuckoos and chasing them away. Helpers in large colonies provision the female so she can spend more time guarding the nest. Hosts learn and recognise their own eggs, and abandon any that are in the nest before they have started their own. Among the cuckoo's adaptations: Mimicry of host eggs. Eggs that are cryptic and therefore unable to be seen in the dark nest. Thickened egg shells. Efficiency in laying the egg, being able to lay an egg secretly and quickly while the host is absent. Media References External links ABID Images On the HBW Internet Bird Collection Horsfield's bronze cuckoo Birds of Australia Horsfield's bronze cuckoo Taxonomy articles created by Polbot Taxobox binomials not recognized by IUCN