Range-dependent flexibility in the acoustic field of view of echolocating porpoises (Phocoena phocoena)

Toothed whales use sonar to detect, locate, and track prey. They adjust emitted sound intensity, auditory sensitivity and click rate to target range, and terminate prey pursuits with high-repetition-rate, low-intensity buzzes. However, their narrow acoustic field of view (FOV) is considered stable throughout target approach, which could facilitate prey escape at close-range. Here, we show that, like some bats, harbour porpoises can broaden their biosonar beam during the terminal phase of attack but, unlike bats, maintain the ability to change beamwidth within this phase. Based on video, MRI, and acoustic-tag recordings, we propose this flexibility is modulated by the melon and implemented to accommodate dynamic spatial relationships with prey and acoustic complexity of surroundings. Despite independent evolution and different means of sound generation and transmission, whales and bats adaptively change their FOV, suggesting that beamwidth flexibility has been an important driver in the ...齿鲸类（Toothed whales）依靠声呐探测、定位并追踪猎物。它们会根据目标距离调整发射声强、听觉灵敏度以及回声定位咔哒声的频率，并以高重复率、低声强的蜂鸣声终止捕猎追踪。然而，过往研究认为其狭窄的声学视场（acoustic field of view, FOV）在接近目标的全过程中保持恒定，这可能会为猎物在近距离逃脱提供便利。本研究表明，如同部分蝙蝠，港湾鼠海豚在攻击的终端阶段会拓宽其生物声呐波束，但与蝙蝠不同的是，它们在该阶段仍可调整波束宽度。基于视频、磁共振成像（magnetic resonance imaging, MRI）以及声学标签（acoustic tag）的录制数据，我们推测这种波束灵活性由额隆（melon）调控，用于适配与猎物间的动态空间关系以及周边环境的声学复杂性。尽管鲸类与蝙蝠的演化路径相互独立，且声波产生与传播的方式截然不同，但二者均会自适应地调整其声学视场，这表明波束宽度灵活性是推动[...]的重要驱动因素之一。