Reynolds D R, Smith A D, Chapman J W
Natural Resources Institute, University of Greenwich, Central Avenue, Chatham, Kent ME4 4TB, UK.
Bull Entomol Res. 2008 Feb;98(1):35-52. doi: 10.1017/S0007485307005470. Epub 2007 Dec 13.
Radar observations have consistently shown that high-altitude migratory flight in insects generally occurs after mass take-off at dusk or after take-off over a more extended period during the day (in association with the growth of atmospheric convection). In this paper, we focus on a less-studied third category of emigration - the 'dawn take-off' - as recorded by insect-monitoring radars during the summer months in southern England. In particular, we describe occasions when dawn emigrants formed notable layer concentrations centred at altitudes ranging from ca. 240 m to 700 m above ground, very probably due to the insects responding to local temperature maxima in the atmosphere, such as the tops of inversions. After persisting for several hours through the early morning, the layers eventually merged into the insect activity building up later in the morning (from 06.00-08.00 h onwards) in conjunction with the development of daytime convection. The species forming the dawn layers have not been positively identified, but their masses lay predominantly in the 16-32 mg range, and they evidently formed a fauna quite distinct from that in flight during the previous night. The displacement and common orientation (mutual alignment) characteristics of the migrants are described.
雷达观测一直表明，昆虫的高空迁徙飞行通常发生在黄昏大规模起飞之后，或者在白天更长时间内起飞之后（与大气对流增强有关）。在本文中，我们关注的是一类较少被研究的迁徙类型——“黎明起飞”，这是在英格兰南部夏季月份通过昆虫监测雷达记录下来的。特别是，我们描述了黎明时分迁徙昆虫形成显著层状聚集的情况，这些聚集集中在距离地面约240米至700米的高度，很可能是因为昆虫对大气中的局部温度最大值做出反应，比如逆温层顶部。在清晨持续数小时后，这些层最终与上午晚些时候（从06:00 - 08:00时起）随着白天对流发展而增强的昆虫活动融合在一起。形成黎明层的物种尚未得到确切鉴定，但它们的质量主要在16 - 32毫克范围内，而且它们显然构成了一个与前一晚飞行的昆虫群落截然不同的动物群落。文中描述了迁徙昆虫的位移和共同取向（相互排列）特征。
