Eggs mimicry of Common Cuckoo (Cuculus canorus) utilizing Ashy-throated Parrotbill (Paradoxornis alphonsianus) host

Polymorphism in egg coloration is prominent in the Common Cuckoo (Cuculus canorus) and a common host, the Ashy-throated Parrotbill (Paradoxornis alphonsianus). Egg polymorphism has probably evolved as a consequence of frequency-dependent selection in both host and parasite, and has, according to human vision, resulted in discrete immaculate white, pale blue and blue egg phenotypes within a single population. However, egg mimicry assessment is not always straightforward, and previous studies have shown that human based comparisons applied to the coloration of bird eggs may be inadequate. Here, we objectively quantify egg color of both parasite and host by spectrophotometry and assess egg mimicry of the Common Cuckoo to the eggs of its Ashy-throated Parrotbill host. Our results revealed that egg reflectance spectra agree well with the assessment based on human vision that cuckoo eggs mimic those of the parrotbill host, in both visible (VIS) and ultraviolet (UV) ranges. However, the white cuckoo egg shows slightly poorer mimicry than the blue cuckoo egg in corresponding host clutches. We suggest that the white parrotbill egg morph (and subsequently the whitish cuckoo egg color) may have evolved after the evolution of the blue egg morph due to strong selection from parasites in the cuckoo-parrotbill system.