Directionality of hearing in two CF/FM bats, Pteronotus parnellii and Rhinolophus rouxi

The head-related transfer function (HRTF) has been measured in two CF/FM bats, Pteronotus parnellii and Rhinolophus rouxi from 575 positions in the frontal hemisphere. P. parnellii showed an increase of the elevation angle of the axis of highest pinna gain with increasing frequency followed by a specific decrease at 75 kHz. Such a drop of elevation angle of the acoustic axis was not seen in R. rouxi. The HRTF further showed a spectral notch dependent on elevation and frequency in P. parnellii, but not in R. rouxi. The functional implications of this difference between both bat species are discussed. Frequencies at maximum pinna gain values did not clearly match the frequencies of the harmonics of the echolocation calls whereas spatial resolution of interaural intensity differences was best in a frequency range that included the higher harmonics of the echolocation calls in both bat species. However, specializations of HRTF patterns matching the exact frequencies of the harmonics of the echolocation calls could not be observed in both bat species.