Although the northern slopes of the hills still are covered with snow and ice in interdune depressions has not melted yet, spring has begun. Eagles and ravens, for which there was no shortage of animal carcasses this winter, returns to their territories. Sky is full of winged travelers going home. Forests and grasslands are full of bird voices. It seems that the bird songs suppress all the other sounds of nature, and yet, if well-listened, from sun shined waters it can be heard something like a cat purring, whereas distant dog barking, there spawn brown frogs and toads. Brown frogs are the very first that start to spawn. Their body is in brown tones. In Latvia there are two brown frog species - the common frog and the moor frog. Both species are difficult to tell apart, but in the spring - mating time, it is a lot easier to do. Frog mating songs are different. Common frogs at spawning site purr as a cat, but moor frog sounds as if something was bubbling in a huge pot. Often these two species are heard in one place. Males of both species during mating time turn bluish. Common frog male at this time obtains bluish dewlap, while moor frog males also have bluish flanks. In addition, the moor frog has more pointed nose and shorter limbs.
Common frogs spend the winter under the water, where they dig into the mud. Most of the moor frogs spend winter on land. At spawning areas first arrive males. When they have found suitable place, they start singing and waiting for females, which arrive later and at the spawning site spends three times shorter time than the males. Rut lasts only 2-3 weeks. Males stick like a limpet to female. Sometimes, unable to find a female, they tend to cling to one another, and even inanimate objects. Females are larger than males and therefore are able to jump around with the lover on her back, as if it was a backpack and nothing more. Female releases spawn at the bottom of water body, at the same time 'backpack' - the male releases sperm and it is done - the spawn is fertilized. After a day pericarp swells up and rises to the surface. Depending on water temperature, sooner or later from the spawn will hatch tadpoles.
At northern coast of Courland in suitable habitats frogs are found in large numbers. In SNP the common frog is occurred more often, but in some places, such as Pēterezera Viga moor frog spawn in large numbers. It is included in the Latvian Red List. As a specially protected brown frogs are included in the appendix of EU Habitats Directive and the Berne Convention. Frog presence gives the evidence of environmental quality. Frogs have priceless role in food chains.