Abstract
The breeding sites and the number of egg masses of Hynobius retardatus and Rana pirica were surveyed in 755ha of the northeast area of Nopporo Natural Forest Park, Hokkaido Japan. There were 53 breeding sites of Hynobius retardatus, and the total number of egg masses was 788. While the sites of Rana pirica were 24, there were 398 in total. Among these respective breeding sites, 17 sites were used by both species. Hynobius retardatus began laying eggs when the water temperatuer was between 7 and 8℃, and increased noticeably when the water temperature reached 10℃. On the other hand, Rana pirica began laying eggs at 10℃C, and egg laying increased noticeably when the water temperature reached 12℃. My research indicates that both species instinctively return to the same breeding sites every breeding season. In order to further research the breeding dynamics of these two species, it is useful to record number of egg masses and breeding sites of both species.
