Use of artificial spawning pools by the Japanese brown frog, Rana japonica, in wet abandoned paddies of Inzai City, Chiba Prefecture, Japan

Abstract

We conducted a survey to determine the breeding status of the Japanese brown frog, Rana japonica, and observe its use of newly constructed spawning pools in Inzai City, Chiba Prefecture. The survey site, approximately 11 ha in area and located at the bottom of a valley, was mostly abandoned rice paddies. During the breeding seasons of 2021 and 2022, we recorded the number and location of egg masses from 29 sections within the overall site. Of more than 500 egg masses observed, more than half occurred in just two sections. In 2022, approximately 10% of the egg masses died, probably because of drying. More than 100 egg masses were laid in two pools constructed through citizen activities, with no eggs found in new rice paddies created near the pools. In habitats with dense spawning sites and often facing drought risks, constructing spawning pools may help reduce early mortality in R. japonica.