Wintering Site Environment for the Nagoya Daruma Pond Frog (Pelophylax porosus brevipodus) in Kurashiki, Okayama Prefecture, Western Japan

Abstract

We conducted field surveys to clarify distribution of the wintering Nagoya Daruma Pond Frog (Pelophylax porosus brevipodus) and the environmental factors affecting wintering site of this species in a rice paddy field and an adjacent fallow paddy field in Kurashiki, Okayama Prefecture, western Japan, where the species inhabits at a high density. The majority of the wintering individuals (34 out of 35) were found in the fallow paddy field. A GLM was fitted using presence and absence of this species as the objective variable, whereas cover rate, plant height, soil pH, volumetric water content, gravimetric water content, degree of saturation, porosity, and topsoil hardness as the explanatory variables. The best model selected based on AIC consisted of soil hardness, cover rate, and the quadratic term of plant height, in which the negative effect of soil hardness was significant. The results insist on the importance of soil hardness and the presence of plants on the topsoil when creating wintering habitat for this frog species in rice paddy fields.