During their annual activity period the toads have 2 or 3 separated calling seasons. The calling activity depends upon the water temperature. The lower limit of the calling activity of the fire-bellied toad is 12.5-13.5°C, the upper limit 30-34°C. The limits of the calling activity of the yellow-bellied toad are lower, the lower limit being 11.5-12° C and the upper limit 26-30° C. 2. According to the fluctuations of the water temperature, the toads demonstrate three different types of calling activity in the course of the year. During the first calling season they croak predominantly in the daytime, whereas they exhibit calling activity in the morning and in the evening or only in the evening during the following calling seasons. 3. Male calling toads occupy circular teritories. The territories of fire-bellied toads have a radius of 1-1.5 meters, whereas those of the yellow-bellied toads have a radius of only 0.5-0.75 meters. In both species the mating calls are territorial in function. 4. The fire-bellied toad has 5 different calls, the normal mating call, the modified mating call, the clasping call and the release calls of first and second order. Not having the release call of first order, the yellow-bellied toad has only 4 calls. The calls consist of harmonically related frequencies and are produced by forcing the air out of the oral cavity through the larynx and into the lungs. In toads the lungs are functional vocal sacs. 5. The mating calls of both species are related to environmental temperature. The repetition rate of calls of both species and the fundamental frequency of the calls of the fire-bellied toad are directly proportional to increasing water temperature. The duration of calls, however, decreases logarithmically with rising temperature. The increasing basic frequency of the yellow-bellied toad's call follows none of the above described patterns. 6. The mating calls of both species also change when the toads grow. Larger animals have a lower fundamental frequency and a longer duration of calls than smaller ones. On the other hand, the number of calls does not depend on the size of the toad and represents the most reliable differential characteristic of toad species.
