Figure 1.
Bird heads [chicken (a, d), rook (b) and duck (c)] modify sound intensity dependent on elevation.
Monaural gain [dB] is displayed at the right ear for multiple sound positions. Coordinates of 0° azimuth and 0° elevation face the beak, −90° azimuth and 0° elevation face the right ear. Sound intensity is projected according to the Hammer projection. Meshgrid spacing is 30°, iso-contourline spacing is 2 dB.
Figure 2.
Contralateral peak position is stable over a wide frequency range.
Positions of the minimum of the upper and lower notch and position of the maximum of the contralateral and ipsilateral peak from 3500 Hz to 5500 Hz in the chicken.
Figure 3.
Monaural spectral cues change systematically along elevation.
Monaural spectral cues between 3000 and 5500 Hz at a specified azimuth position for different elevation positions in the chicken.
Figure 4.
Localization error in elevation is lowest at spatial positions lateral to the head.
The localization error in elevation is based on either the chicken‘s pHRIR (a), mHRIR (b) or both combined (c). The mHRIR‘s differential contribution to reduce elevation error (d) is calculated by subtracting (a) from (c). Spacing of error-contourline is 5°, map orientation in relation to the head and map projection are the same as in Figure 1.
Figure 5.
Schematic interpretation that directionality of vision and hearing align.
Lateral eyed birds like Gallus gallus have access to elevation dependent IIDs on both sides (a) (Figures S4 to S6). Frontal eyed birds like Tyto alba however have access to their elevation dependent IIDs in front (b) [6]. Color indicates changing IID values.