Prey survival by predator intimidation: an experimental study of peacock butterfly defence against blue tits

Abstract

Long-lived butterflies that hibernate as adults are expected to have well-developed antipredation devices as a result of their long exposure to natural enemies. The peacock butterfly, Inachis io, for instance, is a cryptic leaf mimic when resting, but shifts to active defence when disturbed, performing a repeated sequence of movements exposing major eyespots on the wings accompanied by a hissing noise. We studied the effect of visual and auditory defence by staging experiments in which wild-caught blue tits, Parus caeruleus, were presented with one of six kinds of experimentally manipulated living peacock butterflies as follows: butterflies with eyespots painted over and their controls (painted on another part of the wing), butterflies with their sound production aborted (small part of wings removed) and their controls, and butterflies with eyespots painted over and sound production aborted and their controls. The results showed that eyespots alone, or in combination with sound, constituted an effective defence; only 1 out of 34 butterflies with intact eyespots was killed, whereas 13 out of 20 butterflies without eyespots were killed. The killed peacocks were eaten, indicating that they are not distasteful. Hence, intimidation by bluffing can be an efficient means of defence for an edible prey.

Predator mimicry, not conspicuousness, explains the efficacy of butterfly eyespots

“…Predator-prey interactions in nature often involve dynamic encounters between the partners, and eyespots are more likely to appear suddenly in front of the predator. Their intimidating effect has been shown to increase when they are revealed abruptly [12]. This may occur in different ways, through a deimatic display performed by the attacked prey [3,19,34], or simply due to its natural movements (wing tilting, change of position, flight).…”

“…Several studies have confirmed the efficacy of intimidating eyespots in inducing a startle response and improving prey survival [4,[12][13][14][15]. However, Stevens [6] proposed that the intimidating effect of eyespots is merely due to their conspicuousness, and that the features shared with vertebrate eyes (e.g.…”

Eyespots divert attacks by fish

“…A further hypothesis which has been invoked to explain the anti-predator function of eyespots is the predator intimidation hypothesis [2][3][4]16,17]. According to this hypothesis, some eyespots, for example some relatively large eyespots in Lepidoptera, would intimidate potential predators by resembling the eyes of the predator's own enemy [2,18].…”

Primary and secondary defences of squid to cruising and ambush fish predators: variable tactics and their survival value

“…Deimatic defences are sounds, displays and postures that intimidate or bluff (Young 1950;Edmunds 1974). Defensive eyespots are one example of a deimatic display found in frogs (Martins 1989;Lenzi-Mattos et al 2005), cephalopods (Hanlon & Messenger 1996), butterflies and moths (Vallin et al 2005(Vallin et al , 2007Stevens et al 2008aStevens et al , b, 2009. Depending on the capabilities of the prey, deimatic displays may signal a warning of true danger or an attempt to deceive a predator into believing prey are larger or more dangerous than they really are; either way, the intention of such displays is to cause predators to hesitate or abandon their attacks (Humphries & Driver 1970;Hanlon & Messenger 1996).…”