Family: Ranidae - "True Frogs"
Order: Anura - Frogs
Phylum: Chordata - Vertebrates
Red List status: Least Concern
Variable over its range. This is a frog of cool climates, and is largely confined to montane regions in southern parts of its range, and abundant and widespread in a wide range of moist habitats further north, from garden ponds and farmland to woodland. Breeding habitat is most often standing water, including shallow temporary pools, farm and garden ponds, and ditches, but frogs may breed in slow-flowing rivers and streams.
Altitudinal range: 0 - 3,000 m, occurring as high as the snow line in parts of the Alps and Pyrenees.
A terrestrial frog in most of its range which is often active early in the year, occasionally as early as January in northern regions. After breeding, animals usually disperse into surrounding terrestrial habitats for most of the year, where they prefer shaded environments. Most populations return to water to hibernate in late autumn. Southern populations differ in spending most of their time in and around pools or streams, and those in the southwest may forgo hibernation altogether. Animals may travel up to 10km in the breeding season to visit breeding sites.
Food items include insects and other terrestrial arthropods, snails and worms. The diet may include pest species such as mosquitoes, making common frogs a potentially valuable control agent. The larval diet consists mostly of algae and detritus (leaf litter and other organic waste), but may take animal matter in smaller quantities.
Courtship behaviour: Male common frogs gather around breeding sites to form choruses, calling from water to attract mates which they then grasp in amplexus.
Reproductive biology: The common frog's reproductive biology has come to typify the classic image of a frog's life cycle. Animals migrate to breed in early spring, though breeding may extend over several months in warmer areas. Females lay one or two clutches, each of up to 4,500 eggs, in shallow water, which rises to form a mat on the water surface. Clutches from many females are typically laid in the same breeding pool, forming a dense aggregation of eggs and eventually larvae. After fertilisation by the male, eggs develop into free-swimming tadpoles which develop into young froglets over the course of the spring. In the far north of the species' range, where development is slow, tadpole cohorts may overwinter as larvae and complete metamorphosis the following year. In southern populations, development may only take weeks. Metamorphosis occurs earlier in the year than in many species, as does breeding, and this appears to enhance metamorph survival rates in the first year of life.
Lifespan: Common frogs are able to live for over a decade; in the east of their range a lifespan of 17 years has been recorded. Adults reach reproductive maturity at three years of age.
Rana temporaria AmphibiaWeb: Information on amphibian biology and conservation. [web application]. 2008. Berkeley, California: AmphibiaWeb. Available: http://amphibiaweb.org/. (Accessed: Sep 15, 2008)
Arnold, N. and Ovenden, D. (2004) Collins Field Guide: Reptiles & Amphibians of Britain & Europe. HarperCollins, London: 287pp
Ramos, M. 2001. "Rana temporaria" (On-line), Animal Diversity Web. Accessed September 15, 2008 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Rana_temporaria.html.
Common frog. Buckinghamshire, United Kingdom
Other Common Names: European frog, European common brown frog, grass frog.
Most of Europe east to the Urals, western Scandanavia and Khazakstan; absent from Portugal and much of Italy, Spain and the Balkans. The species extends northwards into Scandinavia, and is the only amphibian in the region to occur in the Arctic Circle. It has been introduced to Ireland, which represents the western extent of the species' range.
Adult: The common frog is a member of the European brown frog complex, and can be difficult to distinguish from close relatives. In general appearance, these frogs have relatively long legs and robust bodies (including thick forelimbs in breeding males), extensive webbing on the toes, a prominent tympanum and horizontal pupils. Members of this group can be distinguished from other European pond frogs by their widely-spaced eyes, the presence of a dark facial mask behind the eye, and the presence of dorsolateral folds along the back, which typically lacks green colouring. Additionally, males have a single vocal sac beneath the head, not two that inflate to the sides as in green frogs. Colouration is variable from brown or yellow to olive and various shades of red, but rarely if ever green.
The common frog differs from other brown frogs in possessing relatively short legs in most populations, a distance between the dorsolateral folds (measured from behind the forelimbs) between 1/5.5 and 1/7 of the body length, a tympanum diameter equal to or smaller than the width of the eye, and a small, soft metatarsal tubercle. Patterning consists of dark blotches on the dorsum
and flanks. The underside is pale or yellow, with darker
speckling. The throat may be bluish in breeding males. A dark
inverted V mark may be present between the shoulders.
Males and females can be distinguished by the slightly smaller adult size of males and, more reliably, by the male's white nuptial pads, which are present year-round; they become enlarged and turn dark brown or black in the breeding season.
Call: A low, loud purring sound that may be heard at any time of night or day through the breeding season, normally emitted by multiple males in a chorus.
Similar species: Other brown frogs, in particular the moor frog (Rana arvalis), which has a large, hard metatarsal tubercle. Common frogs rarely have striped patterning and the snout is usually blunt rather than pointed (although this may vary in juveniles), but neither characteristic is definitive. The moor frog also exhibits a preference for more open habitats than the common frog.
Common frogs are similar in size to common toads (Bufo bufo), with which they are often confused by inexperienced nature-lovers, but lack parotid glands and have smooth rather than warty skin.
Details of common frog head, showing widely-separated eyes and part of the facial mask.