Sexual and seasonal differences in the frequency of beak marks on the wings of two Lethe butterflies |
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Authors: | Jun-Ya Ide |
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Institution: | (1) Department of Zoology, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan;(2) Present address: Laboratory of Insect Ecology, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan |
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Abstract: | To assess bird predation pressure on butterflies, I investigated beak marks on the wings of two Lethe butterflies for 3 years in secondary temperate forests. If bird predation had significant effects on average longevity of
butterflies, and if the number of specimens preyed upon was proportionate to the number of beak-marked specimens, the beak
mark frequency would be negatively correlated with average longevity of a butterfly. Bird predation pressure is generally
thought to influence average longevity of butterflies. Therefore, if there is a negative correlation between beak mark frequency
and average longevity, bird predation pressure would be reflected in beak mark frequency. Beak mark frequency was negatively
correlated with longevity in Lethe diana (Butler), the more abundant of the two species; thus, the beak mark frequency was considered to be a suitable index of bird
predation pressure on the butterflies investigated in this study. In both Lethe species, beak mark frequency was higher in females than in males. Because female butterflies have a relatively smaller thorax
and flight muscles and a larger abdomen that contains eggs, they are presumably weaker or less agile fliers than males, and
are probably attacked more easily by birds. In autumn, butterflies were heavily attacked by birds irrespective of sex and
species. Because the numbers of lepidopteran larvae, which are the preferred prey of many birds, decreased in autumn, birds
were thought to shift their diets to alternative prey such as adult butterflies. |
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Keywords: | Bird predation Lepidopteran larvae Longevity Relative thoracic mass Symmetrical mark |
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