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The conspicuous gape of the nestling common Cuckoo Cuculus canorus as a supernormal stimulus for Rufous Bush Chat Cercotrichas galactotes hosts

AuthorsÁlvarez, Fernando
Issue Date2004
PublisherNederlandse Ornithologische Unie
CitationArdea 92: 63- 68 (2004)
AbstractThe Rufous Bush Chat Cercotrichas galactotes is parasitized by the Cuckoo Cuculus canorus. To study how a Cuckoo elicits provisioning by this specific host species, the response of the Rufous Bush Chats to two imitations of the coloration of the gape of Cuckoo nestlings was tested. In pairs of experimental and control own nestlings whose gapes had been artificially coloured, body mass changes were recorded over 2-hr periods. Body mass increase was used as an indicator of the amount of food provided by the parents. Both in the experimental chicks in 20 nests with gapes artificially coloured plain orange (imitating the coloration of the Cuckoo's gape) and in the experimental chicks in 18 nests with gapes coloured to imitate the design of the Cuckoo's gape, body mass increase was higher than in the controls. Experimental chicks apparently received greater amounts of food than the controls. No significant difference was detected between the effects of both experimental treatments. Therefore, in this particular gens of Cuckoo, parasitizing Rufous Bush Chats in southern Spain, either the gape's intense coloration or its characteristic visual pattern may act as supernormal stimuli. So far in other host species no effect of gape coloration has been found. The conspicuous gape colour and pattern could be playing a more important role stimulating food provisioning in Rufous Bush Chats than in other hosts species whose nestlings produce more begging calls. The specific coloration of the Cuckoo chick may have evolved to exploit the provisioning response of hosts towards their own nestlings.
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