Title: Biosonar Navigation above Water I: Estimating Flight Height. Authors: Phone: +49 8161712807

30 Locomotion and foraging on the wing require precise navigation not only in the 31 horizontal plane. Navigation in three dimensions and specifically, precise adjustment 32 of flight height is essential for flying animals. Echolocating bats drink from water 33 surfaces in flight, which requires an exceptionally precise vertical navigation. Here we 34 exploit this behavior in the bat, Phyllostomus discolor, to understand the biophysical 35 and neural mechanisms which allow for sonar-guided navigation in the vertical plane. 36 In a set of behavioral experiments, we show that for echolocating bats, adjustment of 37 flight height depends on the tragus in their outer ears: Specifically, the tragus 38 imposes elevation-specific spectral interference patterns on the echoes of the bats’ 39 sonar emissions. Head-related transfer functions of our bats show that these 40 interference patterns are most conspicuous in the frequency range around 55 kHz. 41 This conspicuousness is faithfully preserved in the frequency tuning and spatial 42 receptive fields of cortical singleand multi-units recorded from anaesthetized 43 animals. In addition, we recorded vertical spatio-temporal response maps, which 44 describe neural tuning in elevation over time. One class of units, which were very 45 sharply tuned to frequencies around 55 kHz, showed unusual spatio-temporal 46