The blue days of moor frog

A pleasant warmth awakens the moor frog (Rana arvalis) from hibernation. The coming spring is luring him out of his winter shelter. He spent the winter hidden in a deep rock crevice, which offered him (overwinter) protection from cold. But this year the shelter was not enough to protect him from freezing.

The moor frog (photo: Goran Šafarek).

Fortunately for the moor frog, freezing isn’t a serious issue. Though the ice crystals forming in the body can harm cells and organs of most animals, frogs and toads are protected by high concentrations of glucose which prevents the damaging freezing of the tissue. And so, even though his heart stopped beating for a while, at the end of February the moor frog awakes alive and kicking.

The male immediately springs into action. His rivals for the females have already started their concert in the nearby pond and there is no time to waste. Their eager singing guides him to the breeding area, which he's been visiting since the age of three, when he became mature enough for mating. Their song resembles the sound of air bubbles escaping from a submerged bottle, but for the female ears, it is a heavenly sound.

When strategically positioned, he joins the choir of a few hundred moor frogs. He knows the females will be able to distinguish his song from all the others and pick him to fertilize their eggs. His skin becomes blue and will remain such for the next few days.

Watch the moor frog singing and mating. 

Captivated by his performance, the first female finds him and he grabs her with his thumb pads. With the male on her back, she lays eggs into the water and he fertilizes them. The females lay their eggs together in a shallow and warm place in the pond, leaving behind a big, soft pillow from which tadpoles will be hatched.

When the breading season ends, the moor frog will leave the pond. He and his mates will travel to their summer residence, which can be as far as one kilometer away in a bright flooded forest or meadow, wetland or a lowland field. There they will catch insects and other invertebrates until autumn, when the cooling air will drive them back into their winter shelters.

Did you know?

- The moor frog is usually 5.5 to 6.0 cm long, but can reach up to 7 cm. It is typically reddish-brown, but the color may vary from yellow to gray. It has a pointed head, a large, dark ear spot, and a lighter belly.

- The moor frogs are native to Europe and Asia. Depending on the location, they hibernate sometime between September and June, and mate between March and June. The mating season starts right after the end of hibernation and lasts for 3-28 days.

- Metamorphosis occurs between June and October. Larvae are about 45 mm long and dark with small metallic dots. Tadpoles eat algae and small invertebrates.

- They are nocturnal, except during breeding season, when they are active day and night.

- The "pillow" made by females can contain up to 3000 eggs.


You can find more beautiful photos of the moorfrogs in Davorin Tome blogpage 
I'm very thankful to Ana Bohte and Katarina Jerin for revising my text.