Reactions of passerine birds to aposematic and nonaposematic firebugs (Pyrrhocoris apterus; Heteroptera)

In spite of the existence of many experimental studies on the function of warning coloration in insects, little is known about the universality of reactions of different predators towards a particular warning signal. Reactions of nine passerine bird species, namely Parus major, Parus caeruleus, Aegithalos caudatus, Erithacus rubecula, Turdus merula, Sylvia atricapilla, Fringilla coelebs, Carduelis chloris and Emberiza citrinella, to the firebug Pyrrhocoris apterus wildtype (brachypterous adults) and its artificially obtained (painted) brown non-aposematic variant were compared. Most insectivorous birds (great tits, blue tits, robins and blackcaps) distinguished between aposematic and non-aposematic bugs, attacking the former less often. Partly granivorous buntings and finches did not distinguish between them, and attacked both variants equally. As all the birds were caught in the wild, the results can be interpreted in terms of the presence of a higher proportion of experienced individuals among insectivorous than among omnivorous species. Two insectivorous species differed from others. The heaviest blackbird attacked and killed aposematic as well as non-aposematic firebugs, and, in contrast, the lightest long-tailed tit avoided both variants. (C) 2003 The Linnean Society of London.