Clamator

Abstract: Birds as brood parasites lay their eggs in the nests of other kinds of birds; these "hosts" incubate and rear the young. In the Old World, cuckoos have long been known as brood parasites. The early Vedic writers of India as well as Aristotle mentioned as common knowledge the fact that cuckoos are reared by other species (42). About 1 % of all bird species are brood parasites, including the honey guides (Indicatoridae), nearly half of the 1 30 species of cuckoos (Cuculidae), two genera of finches (Vidua and Anomalospiza, Ploceidae), five cowbirds (Icteridae), and a duck (Heteronetta atricapilla, Anatidae) (37-42, 9 1-93, 1 14, 1 32, 1 36, 199). No other vertebrate groups with parental care so consistently parasitize other species. [A few freshwater fish do occasionally ( 14).] Counterparts of the cuckoos are known among insects, of which several groups are specialized for interactions with social insects, ranging from facultative commensalism to an inquilinism close to the cuckoo nexus. Some adult insects as well as immature depend completely on their hosts (4, 202). Most parasitic birds are altricial; their nestlings depend on the host for food. The parasitic duck, however, obtains only protection and warmth from the host and feeds and cares for itself shortly after hatching ( 199).

Abstract: Although the cuckoo Cuculus canorus parasitizes a variety of hosts, individual females are thought to favour just one species and they lay eggs coloured to match, more or less accurately, those of their particular host1–3. The mechanisms underlying this division of females into strains, or gentes, specializing on different hosts are unknown. From a study of museum collections we show that the eggs of British cuckoo gentes are statistically different and, using model eggs, we show by experiment that host discrimination against badly matching eggs is a selective force in gens maintenance and that cuckoos lay a better mimetic egg where the host species is apparently more discriminating.

Abstract: SUMMARY (1) There was no difference in the distinctiveness of egg markings between species that have interacted strongly with cuckoos and species that have not, nor in intra-clutch variation, nor in inter-clutch variation within a species. In Iceland, where they are isolated from cuckoos, the eggs of meadow pipits and pied/white wagtails showed no differences in intra-clutch variation, nor inter-clutch variation, from those in parasitized populations in Britain. Thus there was no evidence that host egg patterns evolve in response to cuckoos. (2) None of the four species tested discriminated against an odd chick (another species) in their nest (chaffinch, reed warbler, reed bunting, dunnock). Hosts therefore evolve discrimination against odd eggs but not against odd chicks. (3) The variation in rejection of unlike eggs among different species of suitable cuckoo hosts is not related to the current costs or benefits of rejecting cuckoo eggs. We suggest that the variation represents snap shots in evolutionary time of different stages of a

Abstract: Cuckoo nestlings that evict all other young from the nest soon after hatching impose a high reproductive cost on their hosts1. In defence, hosts have coevolved strategies to prevent brood parasitism. Puzzlingly, they do not extend beyond the egg stage2,3,4,5. Thus, hosts adept at recognizing foreign eggs remain vulnerable to exploitation by cuckoo nestlings6,7. Here we show that the breach of host egg defences by cuckoos creates a new stage in the coevolutionary cycle. We found that defences used during the egg-laying period by host superb fairy-wrens (Malurus cyaneus) are easily evaded by the Horsfield's bronze-cuckoo (Chrysococcyx basalis), a specialist fairy-wren brood parasite. However, although hosts never deserted their own broods, they later abandoned 40% of nests containing a lone Horsfield's bronze-cuckoo nestling, and 100% of nests with a lone shining bronze-cuckoo nestling (Chrysococcyx lucidus), an occasional fairy-wren brood parasite. Our experiments demonstrate that host discrimination against evictor-cuckoo nestlings is possible, and suggest that it has selected for the evolution of nestling mimicry in bronze-cuckoos.