Fig. 1

Bats adjust their mouth gape to control acquisition. A A bat circling the target (“+”). Flight trajectory—black dotted line; beam direction—turquoise (approach beams), magenta (search beams), flight start and direction depicts by bat symbol. The bat performs two approaches in this trial: an initial one with three beams pointed at the target; and a long one, without landing. B Bats increased emission rate, decreased call duration, and increased call peak frequency prior to landing or attempting to land on the target. In both “B” and “C,” the sequence presents two phases—approach and search. Time “0” depicts the first call after the minimal ICI, mean ± SE, n = 5 bats. C The bats controlled their vertical beam-width by widening the gape prior to landing. Simulated vertical (yellow) and horizontal (purple) beam widths. Simulations are averaged for two models based on the average gape of all five bats. D The bats widened their gape when aiming their gaze (head) at the target (X axis shows azimuth relative to target), mean ± SE, n = 5. E1–E2 Schematics illustrating two approach trials. Flight trajectory—black line; echolocation calls—red squares; mouth gape—turquoise shading. F The change in gape as a function of the ICI, mean ± SE, n = 5 bats. G 3D acoustic simulation of the vertical beam-width (two-sided 6 dB) as a function of the emission frequency for the observed two gapes: 2.2 mm—green and 5.7 mm—brown. The average of two models is presented. A piston model of a 7 mm aperture is shown in black. Horizontal and vertical dashed lines depict the bats’ peak frequencies during search and approach, respectively (40 and 50 kHz). H Call peak frequency increased during the approach. Insert shows two call spectrograms and spectra—search in red and approach in turquoise