Beak marks on butterfly wings with special reference to Japanese black swallowtail

Birds are believed to be one of the principal predators of butterflies. The beak marks (BMs) left on the butterfly wings are useful indices of bird predation. We performed 84 collections in grasslands and woodlands during 2002–2006 in Ito, Shizuoka prefecture, and collected 893 specimens belonging to 48 species. In general, the larger was the body size the higher was the BM rate. There were two peaks in the BM rate and the peaks were higher by 13–14 % in autumn than in spring in both grasslands and woodlands. During 2007 and 2008, capture-mark-recapture surveys were conducted 82 times in a flight path of black swallowtail butterflies (BSBs). A total of 443 BSB were individually marked and released at a site 400 m away from the flight path after examining for BM, degree of wing damage, body size, sex and species. The BM% of BSB ranged from 40 to 46 %, which was the highest among the observed butterflies. The recapture rate was negatively correlated with the BM rate suggesting that the avian predation was strong enough to affect the survival rate of BSB adults. In addition, the BM rate showed a delayed positive response to BSB density in the previous month. Variation in the BM rate was analyzed with a multivariate model; it indicated that month and wing length were significant explanatory variables. In addition, the highest BM rate was observed at an intermediate wing size. These results strongly suggested that variation in the BM rate was caused by variation in avian life history and predator size. All the evidence suggested that an appreciable predation pressure by birds operated on BSB adult populations.