Ladegaard Michael, Jensen Frants Havmand, Beedholm Kristian, da Silva Vera Maria Ferreira, Madsen Peter Teglberg
Zoophysiology, Department of Bioscience, Aarhus University, Aarhus 8000, Denmark
Aarhus Institute of Advanced Studies, Aarhus University, Aarhus 8000, Denmark.
J Exp Biol. 2017 Jul 15;220(Pt 14):2654-2665. doi: 10.1242/jeb.159913. Epub 2017 May 19.
Toothed whales have evolved to live in extremely different habitats and yet they all rely strongly on echolocation for finding and catching prey. Such biosonar-based foraging involves distinct phases of searching for, approaching and capturing prey, where echolocating animals gradually adjust sonar output to actively shape the flow of sensory information. Measuring those outputs in absolute levels requires hydrophone arrays centred on the biosonar beam axis, but this has never been done for wild toothed whales approaching and capturing prey. Rather, field studies make the assumption that toothed whales will adjust their biosonar in the same manner to arrays as they will when approaching prey. To test this assumption, we recorded wild botos () as they approached and captured dead fish tethered to a hydrophone in front of a star-shaped seven-hydrophone array. We demonstrate that botos gradually decrease interclick intervals and output levels during prey approaches, using stronger adjustment magnitudes than predicted from previous boto array data. Prey interceptions are characterised by high click rates, but although botos buzz during prey capture, they do so at lower click rates than marine toothed whales, resulting in a much more gradual transition from approach phase to buzzing. We also demonstrate for the first time that wild toothed whales broaden biosonar beamwidth when closing in on prey, as is also seen in captive toothed whales and bats, thus resulting in a larger ensonified volume around the prey, probably aiding prey tracking by decreasing the risk of prey evading ensonification.
齿鲸已经进化到生活在极其不同的栖息地，但它们都强烈依赖回声定位来寻找和捕捉猎物。这种基于生物声纳的觅食过程包括寻找、接近和捕捉猎物的不同阶段，在这个过程中，使用回声定位的动物会逐渐调整声纳输出，以主动塑造感官信息流。要测量这些输出的绝对水平，需要以生物声纳波束轴为中心的水听器阵列，但对于接近和捕捉猎物的野生齿鲸，从未进行过这样的操作。相反，野外研究假设齿鲸在接近阵列时会以与接近猎物时相同的方式调整其生物声纳。为了验证这一假设，我们记录了野生亚河豚在接近并捕捉系在星形七水听器阵列前的水听器上的死鱼时的情况。我们证明，亚河豚在接近猎物时会逐渐缩短点击间隔并降低输出水平，其调整幅度比根据先前亚河豚阵列数据预测的要大。猎物拦截的特点是点击频率高，但尽管亚河豚在捕捉猎物时会发出嗡嗡声，但其点击频率低于海洋齿鲸，导致从接近阶段到嗡嗡声阶段的过渡更加平缓。我们还首次证明，野生齿鲸在靠近猎物时会拓宽生物声纳波束宽度，圈养的齿鲸和蝙蝠也有这种情况，因此在猎物周围形成更大的声纳照射体积，这可能通过降低猎物躲避声纳照射的风险来帮助追踪猎物。
