Rana ridibunda is the largest frog species native to Europe, with adults reaching up to 15 cm in size (1). There is a horizontal pupil present in the eyes (2). It has long hind legs, with the heel extending past the eye (1). There is sexual differentiation between the sexes, as males have paired, grey vocal sacs situated behind the mouth (2).
There is quite a bit of variation in the colour morphs that can be found. The dorsal surface can appear brownish to grey, with a green tint present; occasionally can be found entirely green or grey. Dark spots can be found on the back, which can vary in size and number (1) (2). The belly can be a greyish-white to yellow colour, with an obvious dark spotted pattern (2).
There are approximately 665 species within the genus Rana, of which approximately 29 can be found in Europe (3). It is most similar in appearance to the Pool Frogs (Rana lessonae), and the Edible Frogs (Rana kl. esculenta), which are a hybrid produced between copulations of the Marsh and Pool Frogs (1). Marsh Frogs that are found in the southern regions of their range often have a bright green colouration on their back (1).
Rana ridibunda is a diurnal species, but can also be active at night. It is aquatic and an gregarious species, with some areas of riverbanks obtaining a population of 1000 individuals per kilometre (2). Hibernation takes place from September to December, and will last until January to June, depending on how far south they are found. Hibernation usually takes place in water, and group hibernation is a characteristic of this species (2).
The Marsh Frog is a very vocal species, with many different types of song present in its vocabulary, and will sing throughout the day and night. Efforts are much increased during the breeding season (1).
Mating season starts around one month after hibernation is ceased (2). Males will defend their established territories within the rivers, and form choruses to call for females (1) (2). Females will lay up to 13,000 eggs in a season, typically hidden within aquatic vegetation situated underneath the surface of the water (1). Tadpoles will appear after a week, but may not metamorphose until the following spring as they may hibernate over the winter period (1). Sexual maturity is reached in males when they are two years old, whilst in females it is not reached until they are three (1).
Marsh Frogs occur in all types of water bodies, including ponds, streams, ditches, rivers and lakes. If there is a territory overlap with the Pool or Edible Frogs, then Rana ridibunda will most likely be present in larger water bodies (1). Can often be found basking on lily pads, or banks of rivers, and when in water the head is usually the only part that is visible (1). R. ridibunda can also tolerate a high salinity content in water (2).
This species occurs throughout most of Europe, especially within the central and eastern regions. It can be found in the Balkan peninsular, but not many are present in Albania and Greece. It has been introduced into England, and this is thought to be the case for some scattered populations throughout France (1).
The main component of a tadpoles’ diet is objects that can be found in the benthic zone of water bodies, such as algae, detritus, plants and some invertebrates (2).
Adults tend to consume aquatic and terrestrial insects. As they are a voracious species, they have also been known to eat conspecifics, other amphibians, reptiles, small birds and rodents (2). When weather conditions are undesirable (such as low rainfall), there are increased incidences of cannibalism (2).
Rana ridibunda have been given a status of Least Concern by the IUCN Red List of Threatened Species (3). This is due to their large population sizes, as well as the broad range they are found in. It has also been shown that this species are quite tolerant of environmental pollution (2).
It is also listed under Appendix III of BERN Convention (5).
Description written by Sheridan Willis (2009)
(1) Arnold, E.N., 2004. A field guide to the reptiles and amphibians of Britain and Europe. 2nd ed. London: Harper Collins Publishers
(2) AmphibiWeb: Information on amphibian biology and conservation. 2009. Rana ridibunda in: <http://www.amphibiaweb.org> Downloaded on 08 July 2009
(3) Zipcode Zoo. 2009. Rana ridibunda in: <http://www.zipcodezoo.com/Animals/R/Rana_ridibunda/>
(4) IUCN 2009. IUCN Red List of Threatened Species. Version 2009.1. Rana ridibunda in: <www.iucnredlist.org> Downloaded on 08 July 2009
(5) Europe, C.o., 2002. Convention on the conservation of European wildlife and natural habitats: Bern Convention. [Online] Available at: http://conventions.coe.int/Treaty/FR/Treaties/Html/104-3.htm [Accessed 23 July 2009]