Underground behavior of overwintering Tokyo daruma pond frogs in early spring
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Underground behavior of overwintering Tokyo daruma pond frogs in early spring Naohisa Nakashima1 · Takumi Moriyama2 · Marina Motegi3 · Akira Mori4 · Keiji Watabe5 Received: 10 January 2020 / Revised: 17 September 2020 / Accepted: 22 September 2020 © The International Society of Paddy and Water Environment Engineering 2020
Abstract Although Tokyo daruma pond frogs (Pelophylax porosus porosus) were once commonly observed throughout paddy fields in Japan, their populations have recently declined. The mode by which frogs survive during the overwintering period is largely unknown. In this study, we observed the underground behavior of 12 free-living Tokyo daruma pond frogs that overwintered in paddy soil and a dry field by periodically excavating their overwintering positions from late March to early May. The mean overwintering depth of these frogs was ~ 19.8 cm, with 10 having migrated toward the soil surface (mean depth: ~ 8.6 cm) by late March, and finally, all 11 live frogs migrated further upward close to the soil surface. In addition, males tended to emerge earlier in spring than females. One monitored frog in the paddy soil that migrated close to the soil surface died, presumably from plowing. Aside from the 12 study frogs, several other mutilated frog corpses were found in the paddies. This species starts migrating to the soil surface during the same period when human disturbances begin, making the frogs vulnerable to these disturbances during this period. Consequently, it is necessary to facilitate the emergence of frogs to protect them from human disturbances—e.g., by temporarily filling fields with water. Keyword Amphibian · Emergence · Pelophylax porosus porosus · Rice paddy · Terrestrial hibernation · Underground movement
Introduction Paddy fields provide habitats and breeding sites for many frog species. Frogs are considered as biological indicators of ecosystem health because they thrive in diverse environments and are positioned in the middle nutrient stage of the food web as a food resource for other amphibians, reptiles, and birds (Mattoon 2001). The Tokyo daruma pond frog * Naohisa Nakashima [email protected] 1
Research Faculty of Agriculture, Hokkaido University, Kita 9 Jo, Nishi 9 Chome, Kita‑ku, Sapporo, Hokkaido 060‑8589, Japan
2
Graduate School of Agriculture, Utsunomiya University, 350 Mine‑machi, Utsunomiya, Tochigi 321‑8505, Japan
3
Kawachi Agricultural Development Office, Tochigi Prefec. Gov. 1‑1‑20 Hanawada, Utsunomiya, Tochigi 321‑0974, Japan
4
Natural History Museum and Institute, Chiba, 955‑2 Aoba‑cho, Chuo‑ku, Chiba city, Chiba 260‑8682, Japan
5
NARO, 3‑1‑1 Kannondai, Tsukuba, Ibaraki 305‑8517, Japan
(Pelophylax porosus porosus) has been designated as an indicator species for biodiversity, and as useful for agriculture (Tanaka 2010). Historically, this species was found throughout paddies and their neighboring agricultural waterways. However, recently, the Tokyo daruma pond frog has experienced a substantial population decline and was r
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