Abstract

Animals modify their behaviours and interactions in response to changing environments. In bats, environmental adaptations are reflected in echolocation signalling that is used for navigation, foraging and communication. However, the extent and drivers of echolocation plasticity are not fully understood, hindering our identification of bat species with ultrasonic detectors, particularly for cryptic species with similar echolocation calls. We used a combination of DNA barcoding, intensive trapping, roost and emergence surveys and acoustic recording to study a widespread European cryptic species complex (Pipistrellus pipistrellus and Pipistrellus pygmaeus) to investigate whether sibling bat species could exhibit extreme echolocation plasticity in response to certain environmental conditions or behaviours. We found that P. pygmaeus occupied the acoustic niche of their absent congeneric species, producing calls with P. pipistrellus’ characteristic structure and peak frequencies and resulting in false positive acoustic records of that species. Echolocation frequency was significantly affected by the density of bats and by maternity rearing stage, with lower frequency calls emitted when there was a high density of flying bats, and by mothers while juveniles were non-volant. During roost emergence, 29% of calls had peak frequencies typical of P. pipistrellus, with calls as low as 44 kHz, lower than ever documented. We show that automatic and manual call classifiers fail to account for echolocation plasticity, misidentifying P. pygmaeus as P. pipistrellus. Our study raises a vital limitation of using only acoustic sampling in areas with high densities of a single species of a cryptic species pair, with important implications for bat monitoring.

Significance statement

Ultrasonic acoustic detectors are widely used in bat research to establish species inventories and monitor species activity through identification of echolocation calls, enabling new methods to study and understand this elusive understudied group of nocturnal mammals. However, echolocation call signalling in bats is intrinsically different to that of other taxa, serving a main function of navigation and foraging. This study demonstrates an extreme level of plasticity, showing large variation in call frequency and structure in different situations. We showcase the difficulty and limitation in using acoustic sampling alone for bat monitoring and the complications of setting parameters for species identification for manual and automatic call classifiers. Our observations of call frequency variation correlated with density and absence of congenerics provide novel insights of behavioural echolocation plasticity in bats.

中文翻译：

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异位症中蝙蝠的回声定位可塑性：在对Pipistrellus sp。进行声学鉴定时要格外小心。

摘要

动物会响应不断变化的环境来修改其行为和互动。在蝙蝠中，环境适应性反映在用于导航，觅食和通讯的回声定位信号中。但是，回声定位可塑性的程度和驱动因素尚未完全了解，这阻碍了我们用超声波探测器识别蝙蝠物种，特别是对于具有类似回声定位要求的隐身物种。我们结合使用了DNA条形码，密集诱捕，栖息和出没调查以及声音记录，来研究广泛的欧洲隐性物种复合体（Pipistrellus pipistrellus和Pipistrellus pygmaeus）调查同胞蝙蝠物种是否可以对某些环境条件或行为表现出极大的回声定位可塑性。我们发现，P。pygmaeus占据了它们不存在的同类物种的声学利基，产生了带有P. pipistrellus的特征结构和峰值频率的声音，并导致了该物种的假阳性声音记录。蝙蝠的密度和产妇的孕育阶段对回声频率有显着影响，当蝙蝠的密度高时，回声频率会降低，而未成年的母亲则受到母亲回声的影响。在栖息地出现期间，有29％的电话出现峰值频率为pipistrellus，通话频率低至44 kHz，比以往任何时候都低。我们显示自动和手动呼叫分类器无法解决回声定位可塑性，从而将P. pygmaeus误识别为P. pipistrellus。我们的研究提出了一个严重的局限性，即在高密度的隐性物种对的单个物种的区域中仅使用声音采样，这对蝙蝠的监测具有重要意义。

重要性声明

超声波探测器广泛用于蝙蝠研究，以通过识别回声定位呼叫来建立物种清单并监测物种活动，从而为研究和了解这一难以捉摸的夜间哺乳动物群提供了新的方法。但是，蝙蝠中的回声定位呼叫信令本质上不同于其他类群，具有导航和觅食的主要功能。这项研究表明了极高的可塑性，显示了在不同情况下通话频率和结构的巨大差异。我们展示了仅使用声学采样进行蝙蝠监测的困难和局限性，以及为手动和自动呼叫分类器设置用于物种识别的参数的复杂性。