_Repetition rate._--The repetition rate of the secondary notes, in calls consisting of more than one secondary, was measured for each form. A considerable amount of variation in this parameter was found in all of the taxa (Table 5). This variation probably is due in part to the effect of temperature differences. Repetition rate is the only parameter analyzed for which there is a correlation with the air-temperature, but even here the correlation is weak, probably due to the microenvironmental effects of humidity, air-movement, and other factors in addition to the ambient air temperature that influences the body temperature of the frogs. These rates are nearly alike in both subspecies of _H. microcephala_ and in _phlebodes_. The repetition rates in _H. robertmertensi_ and _H. sartori_ are considerably faster than in the other three taxa. _Hyla sartori_ has the fastest repetition rate of the group. In all characteristics of the mating calls the two subspecies of _H. microcephala_ agree closely, as might be expected, although the differences are statistically significant. _Hyla robertmertensi_ is distinctive in call pattern and seems to be closer to _microcephala_ in dominant frequency but closer to _H. phlebodes_ in fundamental frequency. Thus, it is somewhat intermediate between _microcephala_ and _phlebodes_. The identical pattern and similarity in fundamental and dominant frequencies of the calls of _H. phlebodes_ and _H. sartori_ possibly indicate close relationship. _Geographic variation in call._--_Hyla m. microcephala_ has higher fundamental and dominant frequencies in Costa Rica than in Panamá. In Costa Rican _H. m. underwoodi_ the fundamental and dominant frequencies are lower than in other parts of the range. Frogs of this subspecies recorded in Nicaragua and Honduras have slightly lower dominant frequencies and higher fundamental frequencies than those recorded in Guatemala or Oaxaca. The duration of both primary and secondary notes decreases to the south; samples from Nicaragua and Costa Rica have the shortest notes. Comparison of duration of notes in the two subspecies shows that the Panamanian _H. m. microcephala_ have slightly longer notes than do any _H. m. underwoodi_; the more northern populations of _H. m. underwoodi_ from México most closely approach _H. m. microcephala_ in this characteristic. The calls of _H. robertmertensi_ in Oaxaca have higher dominant and fundamental frequencies and longer secondary notes than do those in Chiapas. The calls of _H. phlebodes_ recorded at Puerto Viejo, Costa Rica, have slightly lower dominant frequencies than do those recorded at Turrialba, Costa Rica, and in Panamá, whereas those recorded at Turrialba have lower fundamental frequencies than in other samples. The duration of notes is slightly shorter in both Costa Rican samples than in those recorded in Panamá. LIFE HISTORY