Brinkløv Signe, Elemans Coen P H, Ratcliffe John M
Sound Communication and Behaviour Group, Department of Biology, University of Southern Denmark, 5230 Odense M, Denmark.
Department of Biology, University of Toronto Mississauga, Mississauga, Ontario, CanadaL5C 1C6.
R Soc Open Sci. 2017 May 24;4(5):170255. doi: 10.1098/rsos.170255. eCollection 2017 May.
Oilbirds are active at night, foraging for fruits using keen olfaction and extremely light-sensitive eyes, and echolocate as they leave and return to their cavernous roosts. We recorded the echolocation behaviour of wild oilbirds using a multi-microphone array as they entered and exited their roosts under different natural light conditions. During echolocation, the birds produced click bursts (CBs) lasting less than 10 ms and consisting of a variable number (2-8) of clicks at 2-3 ms intervals. The CBs have a bandwidth of 7-23 kHz at -6 dB from signal peak frequency. We report on two unique characteristics of this avian echolocation system. First, oilbirds reduce both the energy and number of clicks in their CBs under conditions of clear, moonlit skies, compared with dark, moonless nights. Second, we document a frequency mismatch between the reported best frequency of oilbird hearing (approx. 2 kHz) and the bandwidth of their echolocation CBs. This unusual signal-to-sensory system mismatch probably reflects avian constraints on high-frequency hearing but may still allow oilbirds fine-scale, close-range detail resolution at the upper extreme (approx. 10 kHz) of their presumed hearing range. Alternatively, oilbirds, by an as-yet unknown mechanism, are able to hear frequencies higher than currently appreciated.
油鸱在夜间活动，利用敏锐的嗅觉和极度感光的眼睛觅食水果，并在进出洞穴栖息地时进行回声定位。我们使用多麦克风阵列记录了野生油鸱在不同自然光条件下进出栖息地时的回声定位行为。在回声定位过程中，这些鸟类发出持续时间小于10毫秒的咔嗒声脉冲串（CBs），由数量可变（2 - 8个）、间隔为2 - 3毫秒的咔嗒声组成。在距离信号峰值频率 - 6分贝处，CBs的带宽为7 - 23千赫。我们报告了这种鸟类回声定位系统的两个独特特征。第一，与漆黑无月的夜晚相比，在晴朗有月光的天空条件下，油鸱会减少其CBs中的咔嗒声能量和数量。第二，我们记录到油鸱报告的最佳听觉频率（约2千赫）与其回声定位CBs的带宽之间存在频率不匹配。这种不寻常的信号与感觉系统不匹配可能反映了鸟类在高频听力方面的限制，但仍可能使油鸱在其假定听力范围的上限极端（约10千赫）实现精细尺度、近距离的细节分辨。或者，油鸱通过一种尚不清楚的机制，能够听到比目前所认为的更高的频率。
