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Protected Species


RANA ARVALIS (1214)
Moor Frog

Moorfrosch (Rana arvalis)

Moorfrosch/Moor Frog (Rana arvalis) © Remo Schulze, CC BY-SA 3.0

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At first glance, the Moor Frog resembles the common Grass Frog (Rana temporaria). With a body length of 4.5 to 7.5 centimetres at most, the Moor Frog is the smallest native brown frog. It looks relatively clumsy with its short, pointed muzzle. Both sexes are mostly brown, rarely reddish, yellowish or greyish-coloured, on the upper side. The dorsal side is marked with a variable dark speckled pattern and in most cases with a quite noticeable bright longitudinal line in the middle. The white-yellowish ventral side is usually unspotted. During the mating season, the body colour changes in most males for a few days to a characteristic blue or purple colour. The Moor Frog’s mating call is also unmistakable: a short series of calls like "wuog ... wuog ... wuog", which is performed gurgling and chuckling and sounds like a bottle filled with air that you open under water.

Habitat and biology

The Moor Frog populates a variety of habitat types: It is found in damp and wet meadows, wet heaths, fens and swamps, border areas of peat and transition bogs as well as in alder, birch and pine marsh forests. In these landscapes which are characterized by high groundwater levels, it prefers nutrient-poor, weakly to moderately acidic, fish-free and plant-rich waters for reproduction: ponds, backwaters, ditches, moor waterbodies as well as the shallow and tidal water zones of small to medium-sized lakes and ponds are populated. As hibernating habitat flood-prone shrubs near the spawning grounds probably have a very high importance. Rarely, individuals hibernate at the bottom of waterbodies.

The main calling and spawning season is usually from the end of March to the beginning of April, with appropriate weather conditions even from mid-March or until the end of April. The eggs are attached in one or two strings (500 to 3,000 eggs each) on different plant structures and are similar to those of the common grass frog. Depending on the weather and nutritional conditions, the larvae hatch after 6 to 16 weeks. Depending on the water temperature, the metamorphosis usually takes place from the beginning of June, occasionally until the end of July. The first metamorphosed frogs will go terrestrial in June. Depending on the weather conditions, the development may also last until September. The mobility of the Moor Frog is rather low. The adult animals move only about 1,000 meters away from the spawning waters.

Sexual maturity sets in after two to three years. The life span of the Moor Frog is up to more than ten years in the wild.

Occurrence

In North Rhine-Westphalia, the Moor Frog reaches its south-western distribution limit. The primary distribution of the species lies in the lowlands in the Münsterland area. The species is classified as "Endangered" (EN).

In Lower Saxony, the Moor Frog is listed as "Vulnerable" (VU) in the Red List (2013). It inhabits almost exclusively the lowlands below 100 metres. Reports from the Börden and the hills and mountains are rare exceptions. The Mittelland Canal can be considered as the southern border of the distribution range. Only in the area of Braunschweig there are significant occurrences south of it. At the lower Middle Elbe, the Moor Frog is one of the most common amphibian species besides the common water frog.

Threats

The main threats for the Moor Frog are widespread habitat destruction due to drainage actions, backfilling of shallow water sinks, intensive cultivation and the general eutrophication of the landscape as well as the introduction of fish into previously fish-free or low-populated water bodies. Construction, development, expansion or deepening of the waterbodies, road construction as well as disturbance by traffic, use for leisure activities, pollutant influx and acidification of the water also contribute to the decline of the Moor Frog.

Types of action

Concrete implementation actions to improve the conservation status are the maintenance and restoration of extensive grasslands in lowland areas near to groundwater – combined with provision of sufficient pools and shallow waterbodies. Wetter areas with low agricultural benefits should be taken out of cultivation and left for bank shrubs and sedge reeds. The Moor Frog generally benefits from the restoration of partially turfed moors, provided that the pH-value in the open water does not sink too much into the acidic range. Suitable amphibian protection actions (e.g. amphibian fencing) should also be set up on traffic routes in the migratory corridors.

Actions within phase 1 of the LIFE IP

In the first phase of the project, seven actions which focus on improving the conservation status of the Moor Frog are planned in North Rhine-Westphalia. These actions are generally designed to optimize available habitat, such as the optimization of ponds (habitat types 3130, 3160) through desludging or clearing bank areas, optimizing wetlands and bog habitats (habitat types 4010, 7120, 7140), for example by removal of the seedlings. The new creation of ponds which serve as spawning waters is also planned.

In Lower Saxony, no specific actions for the Moor Frog are planned in the context of the LIFE IP, but synergy effects are to be expected with the implementation of actions for the other focus species and habitat types.

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