Common Frog

Common Frog
Conservation status
Least Concern (IUCN 3.1)[1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Amphibia
Order:	Anura
Family:	Ranidae
Genus:	Rana
Species:	R. temporaria
Binomial name
Rana temporaria Linnaeus, 1758
Subspecies
R. t. temporaria R. t. honnorati R. t. parvipalmata

The Common Frog, Rana temporaria also known as the European Common Frog or European Common Brown Frog is found throughout much of Europe as far north as well north of the Arctic Circle in Scandinavia and as far east as the Urals, except for most of Iberia, southern Italy, and the southern Balkans. The farthest west it can be found is Ireland, where it has long been thought erroneously to be an entirely introduced species.

Appearance

Adult Common Frogs have a body length of 6 to 9 centimetres (2.5 to 3.7in)^[2] and their backs and flanks vary in colour, with olive green^[3] grey-brown, brown, olive-brown, grey, yellowish or rufous possible.^[4] However, Common Frogs are known to be able to lighten and darken their skin in order to match their surroundings.^[3] It is also not unknown for more unusual colouration- both black and red individuals have been found in Scotland, and male Common Frogs have been known to turn greyish blue in the mating season (video on page).^[3] Additionally, albino Common Frogs have been found with yellow skin and red eyes.^[3] Their average weight is 22.7g (0.8oz). Females are usually slightly larger than males.^[5]

Common Frogs' flanks, limbs and backs are covered with irregular dark blotches^[3] and they usually sport a chevron-shaped spot on the back of their neck.^[4] Unlike other amphibians, Common Frogs generally lack a middorsal band, and when they have one, it is comparatively faint.^[4] In many countries the moor frogs do have a light dorsal band which easily distinguishes them from common frogs. The frogs' underbellies are white or yellow (occasionally more orange in females) and can be speckled with brown or orange.^[3] Common Frogs have relatively short hind legs and possess webbed feet.^[3] The legs of the agile frog are much longer which distinguishes them from common frogs along with the agile frog's fainter colouration. Their eyes are brown with transparent horizontal pupils, and they have transparent inner eyelids to protect their eyes while underwater, as well as a 'mask' which covers their eyes and eardrums.^[3]

Male during breeding season showing the nuptial pad, white throat and a blue grey hue over normal the black and brown skin

Males are distinguishable from females due to hard swellings (called nuptial pads^[3]) on their first finger. These are used for gripping females during mating.^[2] Also, during the mating season, males' throats often turn white. A final differentiation can be the colour- during the mating season, males are generally light and greyish in colour, whereas the female is browner, or even red.^[4]

The mating season is short, just a week in March after which the frogs move back to their terrestrial habitat.

Distribution

Distribution of Rana temporaria in Europe

The Common Frog is found throughout much of Europe as far north as northern Scandinavia inside the Arctic Circle and as far east as the Urals, except for most of Iberia, southern Italy, and the southern Balkans. Other areas which the Common Frog has been introduced to include the Isle of Lewis, Shetland, Orkney^[3] and the Faroe Islands.^[6]

Ireland

The Common Frog has long been thought to be an entirely introduced species in Ireland,^[7] however, genetic analyses suggest that particular populations in the south west of Ireland are indeed indigenous to the country.^[8] The authors propose that the Irish frog population is a mixed group that includes native frogs that survived the last glacial period in ice free refugia, natural post-glacial colonisers and recent artificial introductions from Western Europe.^[8][9]

Diet

Adult Common Frogs will feed on any invertebrate of a suitable size, although they do not feed at all during the breeding season.^[3] Favourite foods include insects (especially flies),^[4] snails, slugs and worms.^[3] The frogs catch their prey on their long, sticky tongues.^[3] Their feeding habits change significantly throughout their lives; whereas older frogs will feed only on land, younger frogs will also feed in the water.^[3] Tadpoles are mostly herbivores, feeding on algae, detritus and some plants, although they will also eat other animals in small amounts.^[4]

Habitat and habits

Outside the breeding season, common frogs live a solitary life in damp places near ponds or marshes or in long grass.^[10] They are normally active for much of the year, only hibernating in the coldest months, sometime between August and early June depending on latitude and altitude.^[4] In the most northern extremities of their range they may be trapped under ice for up to nine months of the year, but recent studies have shown that in these conditions they may be relatively active at temperatures close to freezing.^[10] In the British Isles, common frogs typically hibernate from late October to January. They will re-emerge as early as February if conditions are favourable, and migrate to bodies of water such as garden ponds to spawn.^[7] Where conditions are harsher, such as in the Alps, they emerge as late as early June. Common frogs hibernate in running waters, muddy burrows, or in layers of decaying leaves and mud at the bottom of ponds. The oxygen uptake through the skin suffices to sustain the needs of the cold and motionless frogs during hibernation.^[3][4][11]

Breeding

Choir of greyish males and a few brownish females still present in a small pond

Common frogs breed in shallow, still, fresh water such as ponds, with breeding commencing in March. The adults congregate in the ponds, where the males compete for females. The courtship ritual involves croaking, and a successful male grasps the female under the forelegs. During the mating season the males can be recognised by a darkened swelling, the nuptial pad on their 'thumbs'. The actual spawning takes place at night but the courtship rituals are also at daytime. The females, which are generally larger than the males,^[3] lay between 1,000 & 2,000 eggs^[12] which float in large clusters.

Amplexus of a reddish female and male in breeding colors on a spawn covered pond

Conservation status

Common Frogs are susceptible to a number of diseases, including Ranavirus and the parasitic fungus Batrachochytrium dendrobatidis which has been implicated in extinctions of amphibian species around the world.^[13] Loss of habitat and the effect of these diseases has caused the decline of populations across Europe in recent years.^[13] It is thought that the spread of the Chytridiomycota fungus has been facilitated by the effects of global warming.^[14] The common frog is listed as a species of Least Concern on the IUCN Redlist of Threatened Species.^[1]

Predators

Tadpoles are eaten by fish, beetles, dragonfly larvae and birds. Adult frogs have many predators including birds of prey, crows, gulls, ducks, terns, herons, pine martens, stoats, weasels, polecats, badgers and otters.^[15]

Some frogs are killed, but rarely eaten, by domestic cats, and large numbers are killed on the roads by motor vehicles.^[16]

References

1. ^ ^{a b} S. Kuzmin (2008). "Rana temporaria". IUCN Red List of Threatened Species. Version 3.1. International Union for Conservation of Nature. http://www.iucnredlist.org/apps/redlist/details/58734. Retrieved November 4, 2010. 
2. ^ ^{a b} Sterry, Paul (1997). Complete British Wildlife Photoguide. London: HarperCollins. ISBN 0 583 33638 8. 
3. ^ ^{a b c d e f g h i j k l m n o p} "Common frog, grass frog". bbc.co.uk science and nature. BBC. http://www.bbc.co.uk/nature/wildfacts/factfiles/483.shtml. Retrieved 2007-08-09. 
4. ^ ^{a b c d e f g h} Sergius L., Kuzmin (1999-11-10). "Rana temporia". AmphibiaWeb. http://www.amphibiaweb.org/cgi-bin/amphib_query?where-genus=Rana&where-species=temporaria. Retrieved 2007-08-09. 
5. ^ Common frog, grass frog
6. ^ Rana temporaria have established themselves as a wild population in Nólsoy
7. ^ ^{a b} "The Common Frog - (Rana temporaria)". enfo.ie. ENFO. Archived from the original on 28 September 2007. http://web.archive.org/web/20070928111934/http://www.enfo.ie/leaflets/bs33.htm. Retrieved 2007-08-09. 
8. ^ ^{a b} Teacher, A. G. F.; T. W. J. Garner, R. A. Nichols (2009-01-21). "European phylogeography of the common frog (Rana temporaria): routes of postglacial colonization into the British Isles, and evidence for an Irish glacial refugium". Heredity 102 (5): 490–496. doi:10.1038/hdy.2008.133. ISSN 0018-067X. PMID 19156165. 
9. ^ "Irish frogs may have survived Ice Age". Zoological Society of London. March 17, 2009. http://www.zsl.org/science/news/irish-frogs-may-have-survived-ice-age,568,NS.html. 
10. ^ ^{a b} Roots, Clive (2006). Hibernation. Westport, Conn: Greenwood Press. pp. 510,511. ISBN 0-313-33544-3. 
11. ^ Dunlop, David (2004-2-26). "Common Frog final" (PDF). Lancashire BAP. http://www.lbap.org.uk/bap/urban/Microsoft%20Word%20-%20Common%20Frog%20final.pdf. Retrieved 2007-08-09. 
12. ^ The Macdonald Encyclopedia of Amphibians and Reptiles - Rana temporaria 80
13. ^ ^{a b} Eccleston, Paul (28 July 2008). "Appeal for public help to track deadly frog disease". The Daily Telegraph (Telegraph Media Group). http://www.telegraph.co.uk/earth/earthnews/3348137/Appeal-for-public-help-to-track-deadly-frog-disease.html. Retrieved 18 June 2010. 
14. ^ Eccleston, Paul (1 January 2008). "Disease threatens mass extinction of frogs". The Daily Telegraph (Telegraph Media Group). http://www.telegraph.co.uk/earth/earthnews/3320273/Disease-threatens-mass-extinction-of-frogs.html. Retrieved 18 June 2010. 
15. ^ Anon. "Common frog: rana temporaria". All about.... Scottish National Heritage. http://www.snh.org.uk/pdfs/education/commonfrog.pdf. Retrieved 10 November 2010. 
16. ^ RSPB Birds Magazine Summer 2004, page 66

External links

• Amphibians of Europe