On the deterring effect of a butterfly's eyespot in juvenile and sub-adult chickens

Circular patterns, or eyespots, are common anti-predator features in a variety of animals. Two defensive functions have been documented: large eyespots may intimidate predators, whereas smaller marginal eyespots may divert attacks. However, a given eyespot potentially serves both functions, possibly depending on the predator's size and/or experience. Naive predators are potentially more likely to misdirect their attacks towards eyespots; alternatively, their typically smaller size would make them more intimidated by the same eyespots. Here we test how juvenile and sub-adult naive chickens respond to a single eyespot on a butterfly's wing. We presented the birds with dead wall brown butterflies, Lasiommata megera, that had their apical eyespot visi- ble or painted over. We assessed the birds' responses' by (i) scoring their intimidation reaction, (ii) whether they uttered alarm calls and, (iii) if they attacked the butterfly and where they targeted their attacks. Results show that both age categories received higher intimidation scores when offered a butterfly with a visible eyespot. Juveniles were more intimidated by the butterfly than the sub-adults: they received higher intimidation scores and were more prone to utter alarm calls. Moreover, only sub-adults at- tacked and did so by preferentially attacking the butterfly's anterior. We demonstrate an intimidating effect of the type of eyespot that has previously been shown only to divert attacks. We suggest that one and the same eyespot may serve two functions relative to different predators; however, further experiments are needed to disentangle the role of predator identity and its link to size, on- togeny and experience (Current Zoology 61 (4): 749-757, 2015).