Advertisement call description of the exceedingly rare Phrynomantis affinis (Anura: Microhylidae), with comparisons to P. bifasciatus and range extensions for both species

Despite a relatively broad distribution in Africa, the Spotted Rubber Frog, Phrynomantis affinis, is extremely rarely encountered. Only 18 specimens from 12 localities have been collected with a few additional observations recorded. Virtually nothing of the species' natural history is known. We report or summarise new localities and range extensions of P. affinis in Namibia and Zambia and describe the call for the first time. We also compare its call to that of the sister species, P. bifasciatus, describing this call for the first time and noting a considerable range extension. The calls show several key differences, with P. affinis calls generally having a lower dominant frequency, pulse repetition rate, and number of pulses than P. bifasciatus. The calls of Namibian and Zambian P. affinis also show marked differences. These descriptions add valuable natural history information for both species and will considerably improve the field detection of the enigmatic P. affinis.