Fawcett Kayleigh, Jacobs David S, Surlykke Annemarie, Ratcliffe John M
Sound and Behaviour Group, Department of Biology, University of Southern Denmark, Campusvej 55, DK5230 Odense M, Denmark.
Department of Biological Sciences, University of Cape Town, 7701 Rondebosch, South Africa.
Biol Open. 2015 May 18;4(6):693-701. doi: 10.1242/bio.201511908.
Echolocating bats are exposed not only to the echoes of their own calls, but often the signals of conspecifics and other bats. For species emitting short, frequency modulated signals e.g. vespertilionoids, adjustments in both the frequency and time domain have been observed in such situations. However, bats using long duration, constant frequency calls may confront special challenges, since these bats should be less able to avoid temporal and frequency overlap. Here we investigated echolocation call design in the highduty cycle bat, Rhinolophus capensis, as bats flew with either a conspecific or heterospecific in a large outdoor flight-room. We compared these recordings to those made of bats flying alone in the same flight-room, and in a smaller flight room, alone, and hunting tethered moths. We found no differences in duty cycle or peak frequency of the calls of R. capensis across conditions. However, in the presence of a conspecific or the vespertilionoid, Miniopterus natalensis, R. capensis produced longer frequency-modulated downward sweeps at the terminus of their calls with lower minimum frequencies than when flying alone. In the presence of the larger high-duty cycle bat, R. clivosus, R. capensis produced shorter calls than when flying alone or with a conspecific. These changes are similar to those of vespertilionoids when flying from open to more cluttered environments. They are not similar to those differences observed in vespertilionoids when flying with other bats. Also unlike vespertilinoids, R. capensis used calls 15 dB less intense in conspecific pairs than when alone.
能够回声定位的蝙蝠不仅会接收到自身叫声的回声，还常常会接收到同种和其他蝙蝠的信号。对于发出短的、频率调制信号的物种，例如蝙蝠科动物，在这种情况下已观察到其在频域和时域上的调整。然而，使用持续时间长、频率恒定叫声的蝙蝠可能会面临特殊挑战，因为这些蝙蝠在避免时间和频率重叠方面的能力可能较弱。在此，我们研究了高占空比蝙蝠南非菊头蝠的回声定位叫声设计，让蝙蝠在大型室外飞行室中与同种或异种蝙蝠一起飞行。我们将这些录音与在同一飞行室单独飞行、在较小飞行室单独飞行以及捕食系留蛾类时的录音进行了比较。我们发现，在不同条件下，南非菊头蝠叫声的占空比或峰值频率没有差异。然而，在有同种蝙蝠或蝙蝠科的纳塔尔长翼蝠存在时，南非菊头蝠在叫声末尾会产生更长的调频向下扫频，其最低频率比单独飞行时更低。在有体型更大的高占空比蝙蝠南非鞍鼻菊头蝠存在时，南非菊头蝠发出的叫声比单独飞行或与同种蝙蝠一起飞行时更短。这些变化与蝙蝠科动物从开阔环境飞向更复杂环境时的变化相似。它们与蝙蝠科动物与其他蝙蝠一起飞行时观察到的差异不同。同样与蝙蝠科动物不同的是，南非菊头蝠在同种配对时发出的叫声强度比单独飞行时低15分贝。
