Dybowski's Frog

Dybowski's frog is a broad-headed true frog measuring 4.5–7.5cm. Its generally smooth back is tan to dark brown and may carry small protuberances, while the underside is white. Males possess paired vocal sacs used during the breeding season. Populations in northeastern China formerly named Rana chensinensis changbaishanensis are now treated as this species. Its wider range includes the Russian Far East, Korean Peninsula and Japan's Tsushima Island. (Wikipedia, general species account)

The frog usually occupies woodland outside its reproductive season and breeds in stagnant or slow-moving water. Before winter it migrates to hibernation sites that include spring-fed ponds, streams and rivers. Males arrive before females, juveniles precede adults, and aggregations may contain as many as 1,000 hibernating frogs. Studies have also recorded substantial seasonal changes in its physiology and gut microbial community as it enters and emerges from hibernation. (Wikipedia, general species account)