Alytes o. obstetricans produces calls from the beginning of April to the end of August on a gravel slope near Tübingen. The annual calling activity is divided into four calling periods of different lengths. They are largely independent of weather conditions. 2. The calling activity is based on an endogenous rhythm which is influenced by two exogenous factors, air temperature and light intensity. The lower temperature threshold of calling activity is about 7° C and the upper one about 26° C. The "Zeitgeber" (artificial light-dark cycle) can synchronize the endogenous rhythm in any way. The calling and physical activity take place during the dark phase and correspond to a "Bigeminus". 3. Male Alytes produce six functionally different calls: a slowly repeated mating call, a rapidly repeated mating call, two calls of excitement, a release call and a distress call. Female Alyies can likewise produce calls, although of only two types: a mating call and a distress call. The calls of both sexes represent harmonic frequencies, with the exception of the release call and the distress call. 4. The mating call is characterised by the following parameters: repetition rate of calls, fundamental frequency, duration of calls and sound level, all of which vary with a change in air temperature. With increasing air temperature, the repetition rate of calls and the fundamental frequency follow a positive linear regression: the duration of call, on the other hand, becomes logarithmically shorter. There is a rough linear correlation between increasing air temperature and increasing sound level. The fundamental frequency and duration of call also vary with the size of the animals. 5. The larynx of Alytes consists of one cricoid and two arytaenoids. Three pairs of muscles are inserted on the larynx cartilage: M. dilatator laryngis, M. sphincter and M. hyo-laryngeus. These are innervated by two branches of the N. vagus: the R. laryngeus longus and the R. laryngeus brevis.
