The relationship between echolocation-call frequency and moth predation of a tropical bat fauna

The allotonic frequency hypothesis proposes that the proportion of eared moths in the diet should be highest in bats whose echolocation calls are dominated by frequencies Outside the optimum hearing range of moths i.e., < 20 and > 60 kHz. The hypothesis was tested on an ecologically diverse bat assemblage in northern tropical Australia that consisted of 23 species (5 families, 14 genera). Peak frequency of signals of bats within the echolocation assemblage ranged from 19.8 to 157 kHz but was greatest between 20 and 50 kHz. A strong positive relationship existed between peak call frequency and percentage of moths in the diet for a sample of 16 bats from the assemblage representing 13 genera (R-2 = 0.54, p = 0.001). The relationship remained strong when the three species with low-intensity calls were excluded. When the two species with high duty cycle, constant-frequently signals were removed, the relationship was weaker but still significant. In contrast to previous research, eared moths constituted only 54% of moth captures in light traps at bat foraging grounds, and eared moths were significantly larger than non-eared individuals. These results show that the pattern of moth predation by tropical bats is similar to that already established for bat faunas in subtropical and temperate regions.