Moor frog sounds | Rana arvalis | Epic nature field recording ~1 hour

Moor frog (Rana arvalis; Blue frog; żaba moczarowa) is one of the most fascinating amphibians inhabiting Poland. Depending on the weather at the turn of March and April, you can witness an amazing spectacle of moor frog mating in small water reservoirs, along with the awakening of nature. During this period, the males turn a beautiful blue color due to the accumulation of lymph in the subcutaneous lymphatic sinuses. The azure shade of their skin is temporary and only lasts during mating. The moor frog mating call is unmistakable, sounding like "wuog ... wuog ... wuog," resembling a gurgling and chuckling bottle being opened underwater.

The scientific name of this frog is "Rana arvalis," which means "frog of the field" when translated, providing an idea of their preferred habitat. They thrive in open areas like damp meadows, wet heath, marsh forests, and peat bogs with high groundwater levels. In their natural habitat, they can live for up to 11 years.

Mating season occurs between March and June after hibernation. The males arrive at the ponds before the females and form breeding choruses, with their songs similar to those of the agile frog (Rana dalmatina). Their calls can sound like boiling water or air escaping from a submerged empty bottle. Male moor frogs turn blue during the mating season, but only for a few days during peak reproductive activity, while females remain brown. The blue color is conspicuous to human vision, but the greatest change occurs in the ultraviolet region from 350-450 nm, invisible to human vision. Males with brighter blue coloration may signal greater sexual and genetic fitness, but only tadpoles fathered by bright blue individuals have a greater chance of survival when pitted against large beetle larvae than those fathered by dull individuals.

The noticeable blue coloration is for attracting females, and it also helps other frog species recognize male moor frogs and prevents inter-species reproduction. Multimale amplexus, in which multiple males mate with a single female, is the predominant method of mating. Females do not prefer males of a particular size but tend to mate with males that have successfully produced offspring with them in the past.

Rana arvalis is included in Annex IV of the Habitats Directive, which requires all European Union countries to cover it with species protection, including the protection of breeding and resting places. This species is under strict protection in Poland.

Despite the excitement of moor frog mating, they are extremely alert and not easy to record. A slight disturbance is enough to make them disappear into the water. In such cases, it is best to remain calm and still for a moment to observe the interesting species, which will quickly return to their occupied positions.

When listening, apart from the sounds of waking birds, you can also hear the deep grumbling sounds produced by common grass frog (Rana temporaria) males through their vocal sacs, which often inhabit the same areas as the moor frog.

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