Jamming Avoidance Response in Echolocation Calls of the Formosan Leaf-nosed Bat (Hipposideros armiger)

This study focused on jamming avoidance response (JAR) in pairs of the Formosan leaf-nosed bats, Hipposideros armiger, with different echolocation call frequencies. H. armiger emits constant frequency/frequency modulated (CF/FM) echolocation calls with relatively longer call duration. Hypotheses tested in this study were (1) JAR in frequencies: if the difference in peak frequency (CF part) between two individuals is small, bats would show JAR. However, if the difference is large, bats would not show JAR. Furthermore, there would be some JAR in the FM part of H. armiger’s echolocation calls (2) JAR in duration: species emit CF/FM echolocation calls would also shorten duration when flying in pair.
Results showed that pairs with small peak frequency differences expanded peak frequency differences in laboratory. However, pairs with large peak frequency differences reduced peak frequency differences. H. armiger also increased differences in minimum frequency and bandwidth, and emitted echolocation calls with higher minimum frequency and wider bandwidth when they flew in pairs. They reduced call duration when they flew in pairs, just as the hypothesis had predicted. However, results in field study were not always consistent with that in laboratory. This may be due to that we could not distinguish the age of bats flying in pairs, or that the calls we defined as emitted when bats were flying alone may not recorded under such condition.