Vocalizations of Xenopus laevis are generated by central pattern generators (CPGs). Advertisement calls of Xenopus laevis are complex biphasic motor rhythms that consist of alternating slow and fast trills (a train of clicks). We found that advertisement calls are sensitive to temperature; click rates of slow and fast trills linearly accelerate as temperature increases. This rate modification of the vocal rhythms originates in the central pattern generators; a similar linear relation between temperature and compound action potentials in the laryngeal nerve was found in fictive advertisement calls evoked in the isolated brain in vitro, and temperature did not limit the contractile properties of laryngeal muscles within the frequency range of vocalizations. Previously, we have localized the vocal CPGs to the brainstem, but it was not clear whether the biphasic rhythms are generated by a single pattern generator that produces two, alternating rhythms, or by two separate generators. Taking advantage of the temperature sensitivity of the vocal CPG in vitro, we addressed this question by selectively cooling one of the candidate CPG nuclei, the dorsal tegmental area of medulla (DTAM). We found that bilateral cooling of DTAM selectively reduced the fast trill rates without affecting slow trill rates. Thus, we conclude that biphasic vocalizations of males are generated by two CPGs dedicated for each trill type.