Male calling effort and mitochondrial DNA (mtDNA) variation were examined in a breeding chorus of toads from a hybrid zone between Bufo microscaphus and B. woodhousii in central Arizona. The chorus comprised 50 B. microscaphus and 17 hybrids, identified on the basis of morphology and advertisement calls; no pure B. woodhousii were observed. Males produced advertisement calls throughout the early evening, even when relatively large numbers of males (>50) were present at the chorus; active searching and satellite tactics were not observed. Calling efforts (call duration X call rate) of hybrids (23.9%, n= 8) and B. microscaphus (24.9%, n= 19) were similar and comparable to call efforts of B. woodhousii (21.9%, n= 10) from a different [...]