Crypsis versus intimidation—anti-predation defence in three closely related butterflies
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Butterflies that hibernate exhibit particularly efficient defence against predation. A first line of defence is crypsis, and most hibernating butterflies are leaf mimics. When discovered, some species have a second line of defence; the peacock, I. io, when attacked by a predator flicks its wings open exposing large eyespots and performs an intimidating threat display. Here we test the hypothesis that butterflies relying solely on leaf mimicking and butterflies with an intimidating wing pattern, when attacked, exhibit different behavioural suites—because leaf mimicking is best implemented by immobility, whereas intimidating coloration is best implemented by intimidating behaviour. In laboratory experiments blue tits, Parus caeruleus, were allowed 40 min to attack single individuals of three species of butterfly: one relying solely on crypsis, the comma, Polygonia c-album; one relying on intimidating wing pattern in addition to crypsis, the peacock; and one intermediate species, the small tortoiseshell Aglais urticae. The results are in accordance with expectations and demonstrate that: (1) birds take longer to discover the leaf mimicking species, the comma, than the tortoiseshell and the peacock; (2) the comma remained motionless throughout experimental trials but small tortoiseshells and peacocks flicked their wings when attacked; (3) the most intimidating butterfly, the peacock, started flicking its wings at a greater distance from the attacking bird than the small tortoiseshell; and (4) the intimidating pattern and behaviour of peacocks was effective—when discovered, all peacocks survived interactions with blue tits, whereas only 22% of commas and 8% of small tortoiseshells survived.
We thank Birgitta Tullberg, Cecilia Kullberg, Sören Nylin, and two anonymous referees for valuable comments on the manuscript. This study was financially supported by the Swedish Research Council (to C.W.). Birds were captured with permission from the Swedish Bird Ringing Centre (permit 619:M03). Housing of animals and experimental setup was reviewed and approved by the regional ethical committee (permit Linköpings djurförsöksetiska nämnd 49-01). The experiments described herein comply with the current laws of Sweden.
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