Rana pirica is a moderate-sized frog of the Rana temporaria group. Males have a snout to vent length of 46-55 mm and females 54-72 mm. The dorsal color is reddish brown and this frog also has a dark grayish brown temporal mask and hindlimb bars. Its throat, chest, and abdomen are whitish and covered with irregular grayish brown markings. The ventral surface of the legs is bright yellowish orange. It has a robust body and a short head that is slightly wider than long. The snout is triangular, but the tip is rounded in dorsal outline. Its forelimbs are stout, with thick, blunt-tipped, unwebbed fingers lacking discs. Hindlimbs are short, about 2.6 times the length of the forelimbs. The heels overlap when the limbs are held at right angles to body, and the tibiotarsal articulation of an adpressed limb reaches the anterior corner of eye. Toe tips are blunt, lacking discs, and the toes are moderately webbed. There is a dorsolateral fold from the supratympanic fold to the groin. The karyotype is diploid (2n=24), with five large and seven small pairs of chromosomes (Matsui 1991).
Rana pirica has been variously designated Rana temporaria, R. chensinensis, and R. dybowskii. However, when R. pirica was mated with any of these three species, the hybrids were inviable or infertile, which proved it to be an independent species. There is no other brown frog on Hokkaido (Goris 2004).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Japan
R. pirica occurs throughout Hokkaido and possibly on some of the outlying islands. It is found in both forests and grasslands from sea level to about 2000 m on Mt. Taisetsu (Goris 2004). 
Life History, Abundance, Activity, and Special Behaviors
R. pirica breeds from April to May after the spring thaw. They migrate to breeding sites during the day and night, usually in warm weather (from below 10 up to 21 degrees Celsius). Amplectant pairs are often formed on land, on the way to the breeding site (Kuzmin 2006). 
Males have paired vocal sacs and vocal openings at the corner of the mouth. The mating call is a fairly high-pitched squeak repeated 6-7 times.
Females lay eggs in globular masses in still, shallow waters of marshes, temporary puddles, and ponds. The egg masses contain 700-1100 eggs. Much of the egg mass is often above the surface of the water.
Tadpoles are brownish and reach a total length of 45 mm. Their tail is not very long, but the tail fin is high. Both hatching and development occur fairly rapidly (Goris 2004). R. pirica tadpoles have developed two predator-specific morphologies: a salamander-specific 'bulgy morph' (bulgy body and higher tail fin) and a dragonfly-specific 'high-tail morph' (only higher tail fin). The induction of the bulgy morph requires close proximity of the salamander, but the high-tail morph can be remotely cued by the larval dragonfly. There is now an arms race with larval Hynobius retardatus salamanders. The bulgy body morph prevents the gape-limited larval H. retardatus from swallowing the tadpole. So, larval H. retardatus salamanders, when exposed to a high number of R. pirica tadpoles, develop a carnivorous broad-headed morph which is advantageous for consumption of larger prey (Kishida 2005). 
Overwintering of tadpoles is unknown, even at high altitudes. Metamorphosed froglets leave the water well before winter sets in. Juveniles require 2-3 years to reach maturity. In the mountains of Shiretoko Peninsula, as long as 5 years may pass before the frogs are sexually mature. There is little information on the feeding habits, but they are probably similar to those of the other brown frogs of mainland Japan (Goris 2004).
Trends and Threats
Dozens of R. pirica are killed on highways by cars during breeding migrations. Attacks of leeches on adult frogs in ponds and of larval Trichoptera (caddisflies) on their spawn have been recorded (Kuzmin 2006).
Possible reasons for amphibian decline
Disturbance or death from vehicular traffic
Goris, R.C. and Maeda, N. (2004). Guide to the Amphibians and Reptiles of Japan. Krieger Publishing Company, Malabar, Florida.
Kishida, O., and Nishimura, K. (2005). ''Multiple inducible defences against multiple predators in the anuran tadpole, Rana pirica.'' Evolutionary Ecology Research, 7(4), 619-631.
Kuzmin, S. L., Sato, T., Nakabayashi, S., Maslova, I. V., and Narumi, N. (2006). ''Ecological observations on the Ezo Brown Frog (Rana pirica Matsui, 1991) on Hokkaido Island, Japan.'' Russian Journal of Herpetology, 13(2), 117-119.
Matsui, M. (1991). ''Original description of the Brown Frog from Hokkaido, Japan, genus Rana.'' Japanese Journal of Herpetology, 14(2), 63-78.
Originally submitted by: Nichole Winters (first posted 2007-04-02)
Edited by: Kellie Whittaker (2007-06-05)
Species Account Citation: AmphibiaWeb 2007 Rana pirica: Ezo Akagaeru <https://amphibiaweb.org/species/5127> University of California, Berkeley, CA, USA. Accessed Nov 28, 2023.
Feedback or comments about this page.
Citation: AmphibiaWeb. 2023. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 28 Nov 2023.
AmphibiaWeb's policy on data use.