Development of methods to detect hibernation sites of Tokyo Daruma pond frog （<i>Pelophylax porosus porosus</i>）using the PIT Tag system.

Underground behavior of overwintering Tokyo daruma pond frogs in early spring

“…During the wintering survey, we observed 61 dropped tags (~55.0%) and 6 rotting corpses (~5.4%) in district K, and 19 dropped tags (~9.0%) and 6 decayed frogs (~2.8%) in district T. The loss of other tags can be partially attributed to individuals leaving the survey area due to predation or migration and failure to detect underground tags. The latter was mainly a consequence of bumpy surfaces in paddy fields resulting in a narrower tag reception range than the range of 20-25 cm reported by Noda et al (2019). However, the overall rate of refinding the frogs using the PIT tag method, including dropped tags, was high enough to consider it an efficient method for detecting overwintering frogs, especially in fields with a simple structure without a ditch such as those in district K (~73.9%).…”

“…Prior to this study, wild Tokyo daruma pond frogs were captured using either a shrimp net with a 1.2 m handle or by hand, and then inserted with PIT tags (Biomark, BIO12B, length: 12.5 mm, diameter: 2.1 mm, weight: 0.1 g) in the field, and immediately released at the site of capture by following the method of Noda et al (2019). To avoid negative effects on survival or behavior, the PIT tags were inserted into the frogs with a snout-vent length (SVL) of ≥40 mm (Pyke 2005).…”

“…The defined control point was fixed by driving timber piles deep into the exteriors of the paddy fields, such as furrows and banks. The first set of excavations was conducted at the same time when the PIT tags were detected to determine survival and overwintering depths (initial overwintering depths), from November 2017 to January 2018 (Noda et al 2019). The subsequent eight tracking excavations were conducted during the daytime on March 27; April 5, 9, 12, 17, 21, and 27;and May 2, 2018. Moreover, from March 8 to May 31, 2018, the research farmlands were surveyed every day, including days when excavations were not conducted, to check the portable antennae's reactions from the ground surface.…”

“…Only small numbers of previous studies have addressed overwintering in the Tokyo daruma pond frog or the closely related Nagoya daruma pond frog (Pelophylax porosus brevipodus). These studies focused on detecting hibernation sites, such as paddy fields and furrows (Niwa et al 1999;Morita et al 2001;Mizuno et al 2007), an adjacent fallow paddy field (Tada et al 2019), and drylands near their breeding paddies (Noda et al 2019). However, although these studies required a great deal of research, the number of frogs found was not commensurate.…”

“…This is because it is difficult to visually observe Tokyo daruma pond frogs during their overwintering period underground and thus also difficult to elucidate the overwintering ecology of this species (Kusano 2011). Noda et al (2019) embedded passive integrated transponder (PIT) tags with a built-in passive radio frequency identifier (RFID) in the bodies of Tokyo daruma pond frogs to enable the successful detection of individuals that overwinter underground. Following the development of technology to determine a sufficient number of overwintering frogs, Nakashima et al (2018) estimated the period when Tokyo daruma pond frogs emerge.…”