Feeding Ecology of a Fish-eating Pitviper, Gloydius tsushimaensis: Seasonal Change of Foraging Sites

Kodoma, Tomonori Laboratory of Ethological Zoology Department of Zoology Graduate School of Science Kyoto University Kyoto, Japan asukamasuku@gmail.com

The Tsushima Mamushi (Gloydius tsushimaensis) is a pitviper endemic to Tsushima Islands, Japan. I conducted a field survey of foraging ecology of G. tsushimaensis by route-census in a mountainous area along Nita river on the northern Tsushima Island from spring to autumn in 2017 and 2018. I set four census routes: one along the main stream of Nita river and three along road-side-ditches near the river. Whenever I collected snakes, I examined their stomach contents by forced-regurgitation and marked them by ventral clipping for individual identification. In spring I also collected snakes in other small streams in distant places to examine stomach contents. In the route-census, I obtained a total of 89 prey items from stomach contents, including 50 amphibians and 29 fishes. In the side-ditches amphibians were the main diet, whereas in the river fishes were predominant. In spring and autumn amphibians mainly occupied the diet, whereas in summer fishes did. The number of snakes in the river increased in summer and decreased in spring and autumn, whereas that the number in the side-ditches showed the opposite tendency. Twenty of 39 individuals that appeared in the side-ditches in spring and autumn were found in the river in summer. In the small streams, lotic salamanders mainly occupied the diet: seven adult salamanders and four egg sacs of them were contained in 14 stomach contents. These results demonstrate G. tsushimaensis changes foraging sites and prey types seasonally. In addition, the large portion of the diet of the snake consisted of highly aquatic preys; fishes, lotic salamanders and their egg sacs. Taking features as a prey of them into account, G. tsushimaensis may have some morphological specializations. Future study should examine the relationship between the unique foraging ecology and morphological adaptations of the snake.

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