The Selective Brood Parasitism In Oriental Reed Warbler Acrocephalus Orientalis By Common Cuckoo Cuculus Canorus

The arm-race interaction between brood parasite and its hosts has been considered a model study of co-evolution. Common cuckoo (Cuculus canorus) is one of the most typical brood parasites, having hosts more than 100 speices. The host preference has been well confirmed in several gentes of Common cuckoo. Each gens mimics the eggs of one or few host species. However, whether the cuckoo can chooses host nests within population and the factors which may affect the host selection are still controversial. Oriental reed warbler (Acrocephalus orientalis) is the main host for Common cuckoo in Panjin Nature Reserve. This provides an important system to study cuckoo’s selection and mechanisms patterns within the Oriental reed warbler host population. In the study, we investigate the reproduction synchronization, spatial organization and egg mimicry to test the host nest selection of Common cuckoo. Furthermore, the main factors affecting host selection were analyzed by comparing the nest site characteristics, parental body quality, nest defense and egg rejection between parasitized nests and non-parasitized nests.The total parasitism rate on Oriental reed warbler by Common cuckoo 14.7% (n=327), and no evidently annual variation on the parasitism rate beween 2014-2015. The breeding time of Common cuckoo and oriental reed warbler is highly synchronized, range from May to the end of July. The peak of the breeding is highly consistent and mainly concentrates on early June. The cuckoo eggs are perfectly mimetic to Oriental reed warbler eggs, particularly spot size (P= 0.001), spot density (P=0.021) and spot coverage (P=0.015) of cuckoo eggs on side end are better-matching to the warbler eggs in the parasitized nests than non-parasitized nests. By analysis the organization of parasitic egg, the same type of cuckoo eggs have relatively fixed distribution area, which indicates that the female cuckoo has some certain egg-laying territory.No significant differences between hosts in the parasitized and non-parasitized nests on the beak length (male:P=0.642; female:P=0.768); beak wide, tarsus length, wing length, weight, and micro-habitat and landscape nest-site and nest characteristics, and the egg rejection rate to painted blue and brown spot non-mimetic eggs. The number of attacks by female warblers to mounted cuckoo dummy was significant higher in the non-parasitized nests than parasitized nests. This implies that the nest defense on the first line of anti-parasitism by female warbler is effective to counter the cuckoo parasitism. However, no such effect was found in the male warblers.