Tian B, Schnitzler H U
Lehrstuhl Tierphysiologie, Universität Tübingen, Germany.
J Acoust Soc Am. 1997 Apr;101(4):2347-64. doi: 10.1121/1.418272.
Echolocation signals of horseshoe bats (Rhinolophidae) consist of a relatively long component of constant frequency (CF) which is preceded by an initial frequency-modulated (iFM) component and followed by a terminal frequency-modulated (tFM) component. To examine the role of these components in echolocation, four bats were trained to fly from a perch to a landing bar. A dual camera system allowed reconstruction of the flight paths in three dimensions. Echolocation signals were recorded, analyzed, and correlated with the flight behavior of the bats. It was confirmed that during flight the bats compensate the Doppler shifts which are produced by their own flight movement. In free flight they emit per wing beat one single signal of long duration, with little variation in the three signal components. In approach flight the bats reduce pulse duration and interval with decreasing target range. The iFM is not varied with respect to target range, suggesting that this component plays little role in the processing of echolocating a target of interest. The bandwidth of the tFM component is increased while its duration is shortened in proportion to decreasing target range, so that the signal-echo overlap of the FM component is avoided down to a target distance of 15 cm. These concurrent changes suggest that the tFM component is used for ranging. During the last 60 cm of the approach the bats compensated for the increase of echo SPL by lowering the emission level of the CF component by 6-9 dB and that of the tFM component by 9-11 dB per halving of range. The specific signal structure of horseshoe bats is discussed as an adaptation for the hunting of fluttering insects in highly cluttered environments.
菊头蝠科蝙蝠的回声定位信号由一个相对较长的恒定频率（CF）成分组成，该成分之前有一个初始调频（iFM）成分，之后有一个终末调频（tFM）成分。为了研究这些成分在回声定位中的作用，训练了四只蝙蝠从栖木飞向着陆杆。双摄像头系统能够重建三维飞行路径。记录、分析回声定位信号，并将其与蝙蝠的飞行行为相关联。结果证实，在飞行过程中，蝙蝠能够补偿自身飞行运动产生的多普勒频移。在自由飞行中，它们每振翅一次发出一个持续时间长的单一信号，三个信号成分变化很小。在接近飞行时，蝙蝠随着目标距离的减小而缩短脉冲持续时间和间隔。iFM成分不随目标距离变化，这表明该成分在对感兴趣目标进行回声定位的过程中作用不大。tFM成分的带宽增加，而其持续时间与目标距离的减小成比例缩短，从而在目标距离低至15厘米时避免FM成分的信号-回波重叠。这些同时发生的变化表明，tFM成分用于测距。在接近飞行的最后60厘米期间，蝙蝠通过将CF成分的发射水平每减小一半降低6 - 9分贝，将tFM成分的发射水平降低9 - 11分贝，来补偿回波声压级的增加。菊头蝠独特的信号结构被讨论为一种在高度复杂环境中捕食飞舞昆虫的适应性特征。
