Department of Biology, Lund University, Ecology Building, 223 62 Lund, Sweden.
Department of Biology, University of Southern Denmark, 5230 Odense, Denmark.
J R Soc Interface. 2017 Oct;14(135). doi: 10.1098/rsif.2017.0455.
Bats navigate the dark using echolocation. Echolocation is enhanced by external ears, but external ears increase the projected frontal area and reduce the streamlining of the animal. External ears are thus expected to compromise flight efficiency, but research suggests that very large ears may mitigate the cost by producing aerodynamic lift. Here we compare quantitative aerodynamic measures of flight efficiency of two bat species, one large-eared () and one small-eared (), flying freely in a wind tunnel. We find that the body drag of both species is higher than previously assumed and that the large-eared species has a higher body drag coefficient, but also produces relatively more ear/body lift than the small-eared species, in line with prior studies on model bats. The measured aerodynamic power of was higher than predicted from the aerodynamic model, while the small-eared species aligned with predictions. The relatively higher power of the large-eared species results in lower optimal flight speeds and our findings support the notion of a trade-off between the acoustic benefits of large external ears and aerodynamic performance. The result of this trade-off would be the eco-morphological correlation in bat flight, with large-eared bats generally adopting slow-flight feeding strategies.
蝙蝠利用回声定位在黑暗中导航。外部耳朵增强了回声定位，但外部耳朵增加了投影的正面面积，并降低了动物的流线型。因此，外部耳朵预计会降低飞行效率，但研究表明，非常大的耳朵可能通过产生空气动力升力来减轻成本。在这里，我们比较了两种蝙蝠物种（一种大耳蝙蝠和一种小耳蝙蝠）在风洞中自由飞行的定量空气动力学效率测量值。我们发现，两种物种的身体阻力都高于先前的假设，而且大耳物种的身体阻力系数也更高，但与小耳物种相比，它产生的耳/体升力相对更多，这与先前对模型蝙蝠的研究一致。测量的蝙蝠的空气动力功率高于空气动力模型的预测值，而小耳蝙蝠则与预测值一致。大耳物种相对较高的功率导致较低的最佳飞行速度，我们的研究结果支持了大的外部耳朵的声学益处和空气动力学性能之间存在权衡的观点。这种权衡的结果将是蝙蝠飞行中的生态形态学相关性，大耳蝙蝠通常采用缓慢飞行的觅食策略。
