Wing-shaking and wing-patch as nestling begging strategies: their importance and evolutionary origins

Avian chicks use different begging strategies when soliciting parental care. A novel begging strategy was recently observed in Horsfield’s hawk-cuckoo Hierococcyx hyperythrus (=Cuculus fugax). Chicks of this brood-parasitic species raise and shake their wings and display to fosterers a gape-coloured patch on the undersides of their wings. Although the gape-coloured wing-patch may be a unique trait of Horsfield’s hawk-cuckoo, wing-shaking in the context of begging is virtually universal in both brood parasites and their hosts. A simple qualitative comparison across different avian taxa suggests that wing-shake begging is most probably an ancestral feature of cuckoos and perhaps all altricial birds. The wing-shaking may be an honest signal of chick quality. It could also reduce the risk of predation if wing-shaking was coupled with reduced loudness of begging. Horsfield’s hawk-cuckoo chicks could have exploited the universal pre-existing host responsiveness to wing-shake begging. Evolution could have then further proceeded by making the wing-shaking more conspicuous by addition of another stimulus—the unique colourful wing-patch. I also hypothesize that wing-shake begging may have evolved from pre-fledging restlessness and is used secondarily in courtship displays, threatening postures, and distraction displays by adults. Further discussions and tests of these hypotheses may facilitate research into the so far unstudied phylogenetic history of avian chick-begging strategies. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.