Garstang M, Larom D, Raspet R, Lindeque M
Department of Environmental Sciences, University of Virginia, Charlottesville 22903, USA.
J Exp Biol. 1995 Apr;198(Pt 4):939-51. doi: 10.1242/jeb.198.4.939.
Atmospheric conditions conducive to long-range transmission of low-frequency sound as used by elephants are found to exist in the Etosha National Park in Namibia during the late dry season. Meteorological measurements show that strong temperature inversions form at the surface before sunset and decay with sunrise, often accompanied by calm wind conditions during the early evening. These observations are used in an acoustic model to determine the sensitivity of infrasound to the effects of (a) the strength, thickness and elevation of temperature inversions, and (b) the growth and decay of an inversion typical of dry, elevated African savannas. The results suggest that the range over which elephants communicate more than doubles at night. Optimum conditions occur 1-2 h after sunset on clear, relatively cold, calm nights. At these times, ranges of over 10 km are likely, with the greatest amplification occurring at the lowest frequency tested. This strong diurnal cycle in communication range may be reflected in longer-lasting changes in weather and may exert a significant influence on elephant behaviour on time scales from days to many years.
研究发现，在纳米比亚埃托沙国家公园旱季后期，存在有利于大象所使用的低频声音进行远距离传播的大气条件。气象测量表明，日落前地表会形成强烈的逆温层，日出时逆温层消散，傍晚时分通常伴有静风状况。这些观测结果被用于一个声学模型，以确定次声对以下因素影响的敏感度：（a）逆温层的强度、厚度和高度；（b）非洲干燥、地势较高的稀树草原典型逆温层的形成和消散。结果表明，大象夜间交流的范围增加了一倍多。最佳条件出现在日落后1 - 2小时，天气晴朗、相对寒冷且平静的夜晚。在这些时段，传播范围可能超过10公里，在测试的最低频率处放大效果最为显著。这种交流范围强烈的昼夜循环可能反映在天气的长期变化中，并可能在从数天到多年的时间尺度上对大象的行为产生重大影响。
