Head–beam coordination in FM and CF-FM bats reveals distinct echolocation strategies during obstacle avoidance flight

Bats navigate in darkness by steering their sonar beams, but how head–beam coordination varies across species with contrasting emission systems remains poorly understood. We examined the oral-emitting FM bat Miniopterus fuliginosus (family Vespertilionidae) and the nasal-emitting CF-FM bat Rhinolophus nippon (family Rhinolophidae) during free-flight obstacle avoidance. Using a motion capture system to track head direction and a 24-channel microphone array to reconstruct sonar beam direction, we quantified angular offsets defined as the angle between head direction and pulse emission direction. Miniopterus fuliginosus exhibited tight head–beam coordination, validating assumptions from head-fixed studies. By contrast, R. nippon showed substantially larger offsets together with a significantly narrower horizontal beam width, a morphological and acoustic constraint that reduces instantaneous spatial coverage. Correspondingly, R. nippon actively shifted its beam between pulse groups, compensating for this restricted beam width and achieving spatial exploration comparable to the broader-beamed M. fuliginosus . Our findings demonstrate divergent acoustic gaze strategies: FM bats employ stable head–beam coordination, while CF-FM bats achieve flexible beam steering. These results highlight how emission mode and flight morphology jointly shape sensorimotor strategies for spatial perception in complex environments, providing evidence for species-specific adaptations in echolocation.