page_title: Cuckoo
section_title: Brood parasitism
hierarchical_section_title: Cuckoo / Behaviour and ecology / Breeding / Brood parasitism
caption_attribution_description: Brush_Cuckoo (Cacomantis variolosus) Kobble Creek, SE Queensland, Australia
context_page_description: The cuckoos are a family of birds, Cuculidae, the sole taxon in the order Cuculiformes. The cuckoo family includes the common or European cuckoo, roadrunners, koels, malkohas, couas, coucals and anis. The coucals and anis are sometimes separated as distinct families, the Centropodidae and Crotophagidae respectively. The cuckoo order Cuculiformes is one of three that make up the Otidimorphae, the other two being the turacos and the bustards.
  The cuckoos are generally medium-sized slender birds. Most species live in trees, though a sizeable minority are ground-dwelling. The family has a cosmopolitan distribution, with the majority of species being tropical. Some species are migratory. The cuckoos feed on insects, insect larvae and a variety of other animals, as well as fruit. Some species are brood parasites, laying their eggs in the nests of other species, but the majority of species raise their own young.
  Cuckoos have played a role in human culture for thousands of years, appearing in Greek mythology as sacred to the goddess Hera. In Europe, the cuckoo is associated with spring, and with cuckoldry, for example in Shakespeare's Love's Labour's Lost.
context_section_description: About 56 of the Old World species and 3 of the New World species (pheasant, pavonine, and striped) are brood parasites, laying their eggs in the nests of other birds. These species are obligate brood parasites, meaning that they only reproduce in this fashion. The best-known example is the European common cuckoo. In addition to the above noted species, yet others sometimes engage in non-obligate brood parasitism, laying their eggs in the nests of members of their own species in addition to raising their own young.  The shells of the eggs of brood-parasites are usually thick. They have two distinct layers with an outer chalky layer that is believed to provide resistance to cracking when the eggs are dropped in the host nest. The cuckoo egg hatches earlier than the host's, and the cuckoo chick grows faster; in most cases the chick evicts the eggs or young of the host species. The chick has no time to learn this behavior, so it must be an instinct passed on genetically. The chick encourages the host to keep pace with its high growth rate with its rapid begging call and the chick's open mouth which serves as a sign stimulus.
  Since obligate brood parasites need to successfully trick their host in order for them to reproduce, they have evolved adaptations at several stages of breeding. However, there are high costs of parasitism on the host, leading to strong selections on host to recognize and reject parasitic eggs. The adaptations and counter-adaptations between host and parasites have led to a coevolution arms race. This means that if one of the species involved were to stop adapting, it would lose the race to the other species, resulting in decreased fitness of the losing species. The egg-stage adaptation is the best studied stage of this arms race.
  Cuckoos have various strategies for getting their eggs into host nests. Different species use different strategies based on host defensive strategies. Female cuckoos have secretive and fast laying behaviors, but in some cases, males have been shown to lure host adults away from their nests so that the female can lay her egg in the nest. Some host species may directly try to prevent cuckoos laying eggs in their nest in the first place – birds whose nests are at high risk of cuckoo-contamination are known to 'mob' cuckoos to drive them out of the area. Parasitic cuckoos are grouped into gentes, with each gens specializing in a particular host. There is some evidence that the gentes are genetically different from one another.
  Female parasitic cuckoos sometimes specialize and lay eggs that closely resemble the eggs of their chosen host. Some birds are able to distinguish cuckoo eggs from their own, leading to those eggs least like the host's being thrown out of the nest. Parasitic cuckoos that show the highest levels of egg mimicry are those whose hosts exhibit high levels of egg rejection behavior. Some hosts do not exhibit egg rejection behavior and the cuckoo eggs look very dissimilar from the host eggs. It has also been shown in a study of the European common cuckoos that females will lay their egg in the nest of a host that has eggs that look similar to its own. Other species of cuckoo lay "cryptic" eggs, which are dark in color when their hosts' eggs are light. This is a trick to hide the egg from the host, and is exhibited in cuckoos that parasitize hosts with dark, domed nests. Some adult parasitic cuckoos completely destroy the host's clutch if they reject the cuckoo egg. In this case, raising the cuckoo chick is less of a cost than the alternative, total clutch destruction.
  There are two main hypotheses on the cognitive mechanisms that mediate host distinguishing of eggs. One hypothesis is true recognition, which states that a host compares eggs present in its clutch to an internal template (learnt or innate), to identify if parasitic eggs are present. However, memorizing a template of a parasitic egg is costly and imperfect and likely not identical to each host's egg. The other one is the discordancy hypothesis, which states that host compares eggs in the clutch and iden
caption: About this soundThe call (help·info) of the brush cuckoo
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