Moor Frog (Rana arvalis)
The family the moor frog belongs to, Ranidae, is a broad group containing 605 species. The family is like a “catch-all” for ranoid frogs that do not belong to any other families. Since this is the case, the characteristics that define them are more general, and the frogs are found all throughout the world, on every continent but Antarctica.
The moor frog’s genus, Rana, is a little more specific. Frogs of this genus are found in Europe, Asia, South America, and North America. The moor frog is not found in either of the Americas, unlike the foothill yellow-legged frog, Cascades frog, and Columbia spotted frog, which are all found in North America.
The moor frog’s scientific name, Rana arvalis means “frog of the fields”. It is also called the Altai brown frog because frogs from the Altai Mountains in Asia have been included in the R. arvalis species. The Altai frogs have some different characteristics such as shorter shins, but currently there is no official distinction and all frogs are placed under Rana arvalis.
This is a small frog, characterized by an unspotted belly, a large, dark ear spot, and — often, not always — a pale stripe down the center of the back. They are generally described as a reddish-brown, but can also be yellow, gray, or light olive. Their bellies are white or yellow and they have a “bandit-like” black stripe going from their nose to their ears. They vary from 5.5 to 6.0 cm long, but can reach up to 7.0 cm in length, and their heads are more tapered than those of the Common frog (Rana temporaria). The skin on their flanks and thighs is smooth, and the posterior part of their tongues is forked and free. They have horizontal pupils, their feet are partially webbed, and their back legs are shorter than those of other species of frogs. The males are different from the females because of the nuptial pads on their first fingers and their paired guttural vocal sacs.
The frogs can be found inhabiting an area stretching from the lowlands of Central and Southern Europe to Siberia, in Austria, Belarus, Belgium, Czech Republic, Denmark, Estonia, Finland, France, Germany, Hungary, Italy, Latvia, Lithuania, Moldova, Netherlands, Norway, Poland, Romania, Russian Federation, Slovakia, Slovenia, Sweden, Switzerland, and Ukraine. However, they are believed to be extinct in Switzerland and maybe Siberia, as well. The records of frogs being in Siberia at all possibly were in error. Alsace, France, constitutes the western boundary of their territory.
The types of land they can inhabit are greatly varied. They live in tundra, forest tundra, forest, forest steppe, and steppe, forest edges and glades, semideserts, swamps, meadows, fields, bush lands, and gardens. They prefer areas untouched by humans, such as damp meadows and bogs, but they still may be able to live in agricultural and urban areas.
Moor frogs will hibernate sometime between September and June, depending on the latitude of the location. Frogs in southwestern, plains areas will disappear later (around November or December) and return earlier (February). Frogs in cold, polar areas, though, will disappear sooner (in September) and return later (in June).
The mating season takes place between March and June right after the end of hibernation. Males form breeding choruses, and their songs sound similar to those of the agile frog, (Rana dalmatina). Their calls can “sound like air escaping from a submerged empty bottle: ‘waug.…waug….waug’. Males can also develop bright-blue coloration for a few days during the season.
The spawning happens very quickly and is completed in three to 28 days. The spawn of each frog is laid in one or two clusters of 500-3000 eggs in warm, shallow waters like in ponds.
Metamorphosis happens between June and October. Larvae are about 45 mm long and colored dark with small metallic dots. When they become tadpoles, they eat algae and small invertebrates. The adult frogs’ feeding is halted during the breeding season, but their diets consist of insects and various invertebrates.
When moor frogs on land sense a threat, they will make a large jump and bury themselves in soil or grass.
This species faces few major threats and is on the IUCN‘s Lowest Concern list. There are problems, though, with destruction and pollution of its habitat and breeding grounds through urbanization, etc., where people overwhelm their environments. Droughts and predation can also cause problems, but overall it quite adaptable and its population trend is considered stable.
Extensive scientific experiments have been performed on moor frogs in an attempt to understand them better. This species is known to have a limited decline in population, but increased acidity levels in breeding areas might be a problem. Studies have shown, when moor frogs are exposed to acidity, they are able to adapt to it and their populations survive.