Fearless distasteful butterflies and timid mimetic butterflies: comparison of flight initiation distances in Papilioninae.

Prey are expected to flee from an approaching predator when the cost of remaining (i.e. being captured) exceeds the cost of fleeing. In species where individuals experience less predation pressure, delayed escape responses to predatory threats are predicted. Therefore, non-chalant behaviour should be observed in unpalatable and Batesian mimetic prey while rapid escape behaviour may be displayed in palatable and non-mimetic prey from closely related species. This study compared the flight initiation distances (FIDs; the distances at which a prey starts to flee during a standardized human approach) of several sympatric swallowtail butterflies (Papilionidae) in two areas with different temperate zones. As predicted, it was found that unpalatable species had significantly shorter FIDs than palatable species in both areas. By contrast, FIDs of Batesian mimic species were significantly longer than those of unpalatable model species and were not significantly different from those of palatable species. FIDs were not significantly different between mimetic and non-mimetic forms of the intraspecific polymorphic species Papilio polytes. The mimetic species or form may reduce the risk of revealing their identity (i.e. palatability) through early escape behaviour. These findings have implications for the selective forces that affect the escape tendency of prey.