Audiograms of a South Indian bat community

Summary

• 1. Audiograms are recorded from one non-echolocating and nine echolocating sympatrically living bat species of South India. These species areCynopterus sphinx (non-echolocating),Tadarida aegyptiaca, Taphozous melanopogon, T. kachhensis, Rhinopoma hardwickei, Pipistrellus dormeri, P. mimus, Hipposideros speoris, H. bicolor andMegaderma lyra.

• 2. InRhinopoma hardwickei a highly sensitive frequency range was found which is narrowly tuned to the frequency band of the bat's CF-echolocation call (32–35 kHz, Fig. 3). In hipposiderids a ‘filter’ narrowly tuned to the frequency of the CF-part of the CF-FM echolocation sounds (137.5 kHz inH. speoris and 151.5 kHz inH. bicolor, Fig. 5) could be recorded from deeper parts of IC.

• 3. In the echolocating species the best frequency of the audiograms closely matched with that frequency range in the echolocation calls containing most energy.

• 4. In bat species foraging flying prey best frequencies of audiograms and height of preferred foraging areas are inversely related, i.e. bat species hunting high above canopy have lower best frequencies than those foraging close to or within canopy (Fig. 6).

• 5. A hypothesis is forwarded explaining how fluttering target detection by constant frequency echolocation might have evolved from long distance echolocation by pure tone signals.