Abstract
BackgroundMany animals reduce the risk of being attacked by a predator through crypsis, masquerade or, alternatively, by advertising unprofitability by means of aposematic signalling. Behavioural attributes in prey employed after discovery, however, signify the importance of also having an effective secondary defence if a predator uncovers, or is immune to, the prey’s primary defence. In butterflies, as in most animals, secondary defence generally consists of escape flights. However, some butterfly species have evolved other means of secondary defence such as deimatic displays/startle displays. The European swallowtail, Papilio machaon, employs what appears to be a startle display by exposing its brightly coloured dorsal wing surface upon disturbance and, if the disturbance continues, by intermittently protracting and relaxing its wing muscles generating a jerky motion of the wings. This display appears directed towards predators but whether it is effective in intimidating predators so that they refrain from attacks has never been tested experimentally.Methodology/Principal FindingsIn this study we staged encounters between a passerine predator, the great tit, Parus major, and live and dead swallowtail butterflies in a two-choice experiment. Results showed that the dead butterfly was virtually always attacked before the live butterfly, and that it took four times longer before a bird attacked the live butterfly. When the live butterfly was approached by a bird this generally elicited the butterfly’s startle display, which usually caused the approaching bird to flee. We also performed a palatability test of the butterflies and results show that the great tits seemed to find them palatable.Conclusions/SignificanceWe conclude that the swallowtail’s startle display of conspicuous coloration and jerky movements is an efficient secondary defence against small passerines. We also discuss under what conditions predator-prey systems are likely to aid the evolution of deimatic behaviours in harmless and palatable prey.
Highlights
Most species are subjected to predation as evidenced by ubiquitous morphological and behavioural traits that have evolved to minimise the risk of being attacked and killed
Another defence that several prey species employ when attacked by predators is startle displays which typically consist of a sudden exposure of conspicuous colours and patterns which are often accompanied by other stimuli such as sounds [1]
A majority (24 of 27) of the European swallowtail butterflies survived our experiment of being confined in a small room with a passerine predator
Summary
Most species are subjected to predation as evidenced by ubiquitous morphological and behavioural traits that have evolved to minimise the risk of being attacked and killed. Secondary defence includes a variety of responses such as evasion, deflection of attacks and death feigning [1,6] Another defence that several prey species employ when attacked by predators is startle displays (or ‘deimatic behaviour’) which typically consist of a sudden exposure of conspicuous colours and patterns which are often accompanied by other stimuli such as sounds [1]. The European swallowtail, Papilio machaon, employs what appears to be a startle display by exposing its brightly coloured dorsal wing surface upon disturbance and, if the disturbance continues, by intermittently protracting and relaxing its wing muscles generating a jerky motion of the wings This display appears directed towards predators but whether it is effective in intimidating predators so that they refrain from attacks has never been tested experimentally
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