Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus, Denmark
Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus, Denmark.
J Exp Biol. 2019 Aug 19;222(Pt 16):jeb206169. doi: 10.1242/jeb.206169.
Echolocating mammals generally target individual prey items by transitioning through the biosonar phases of search (slow-rate, high-amplitude outputs), approach (gradually increasing rate and decreasing output amplitude) and buzzing (high-rate, low-amplitude outputs). The range to the main target of interest is often considered the key or sole driver of such biosonar adjustments of acoustic gaze. However, the actively generated auditory scene of an echolocator invariably comprises a large number of other reflectors and noise sources that likely also impact the biosonar strategies and source parameters implemented by an echolocating animal in time and space. In toothed whales, the importance of context on biosonar adjustments is largely unknown. To address this, we trained two harbour porpoises to actively approach the same sound recording target over the same approach distance in two highly different environments: a PVC-lined pool and a semi-natural net pen in a harbour, while blind-folded and wearing a sound recording tag (DTAG-4). We show that the approaching porpoises used considerably shorter interclick intervals (ICIs) in the pool than in the net pen, except during the buzz phase, where slightly longer ICIs were used in the pool. We further show that average click source levels were 4-7 dB higher in the net pen. Because of the very low-level in-band ambient noise in both environments, we posit that the porpoises adapted their echolocation strategy to the different reverberation levels between the two settings. We demonstrate that harbour porpoises use different echolocation strategies and biosonar parameters in two different environments for solving an otherwise identical target approach task and thus highlight that biosonar adjustments are both range and context dependent.
回声定位哺乳动物通常通过经历生物声纳的搜索（慢速率、高振幅输出）、接近（逐渐增加的速率和降低的输出振幅）和嗡嗡声（高速率、低振幅输出）阶段来定位单个猎物。目标物的距离通常被认为是这种生物声纳调整声焦点的关键或唯一驱动力。然而，回声定位器主动生成的听觉场景通常包含大量其他反射器和噪声源，这些源可能也会影响回声定位动物在时间和空间上实施的生物声纳策略和源参数。在齿鲸中，背景对生物声纳调整的重要性在很大程度上是未知的。为了解决这个问题，我们训练了两头宽吻海豚，让它们在两个非常不同的环境中，以同样的接近距离主动接近同一个声音记录目标：一个 PVC 衬里的水池和一个港口的半自然网箱，同时蒙住眼睛并戴上声音记录标签（DTAG-4）。我们发现，在水池中，接近的海豚使用的短间隔时间（ICIs）明显比在网箱中短，除了在嗡嗡声阶段，在水池中使用的 ICIs 略长。我们还发现，平均点击源级在网箱中高 4-7dB。由于在这两个环境中，带内环境噪声非常低，我们假设海豚适应了不同环境的混响水平，从而改变了它们的回声定位策略。我们证明，在解决完全相同的目标接近任务时，港湾海豚在两个不同的环境中使用不同的回声定位策略和生物声纳参数，因此突出表明生物声纳调整既与距离有关，也与背景有关。
