Coverdill Alexander J, Bentley George E, Ramenofsky Marilyn
Department of Biology, University of Washington, Seattle, WA 98195, USA.
J Biol Rhythms. 2008 Feb;23(1):59-68. doi: 10.1177/0748730407311456.
Avian migration is a seasonal activity that requires intricate timing on both an annual and daily basis. With increasing evidence for endogenous regulation of daily activities in migrant species, we tested whether a circadian oscillator may be involved with the expressions of daily locomotor activities and specific behaviors of the long-distance migrant, Gambel's white-crowned sparrow (Zonotrichia leucophrys gambelii). Our previous studies have identified both daytime and nighttime behavioral patterns under a photoperiod of 18L:6D. In 2 separate trials, birds in the vernal migratory life-history stage were exposed to constant dim light, (DD)dim, and constant bright light, LL, while locomotor activity and behavioral observations were collected. Under (DD)dim, the daytime behaviors that included active and quiescent components observed under 18L:6D were lost as migratory restlessness, the intense nighttime activity, persisted nonstop for 36.4 h. Furthermore, the specific behaviors of migratory restlessness that are normally confined to the dark phase of 18L:6D, beak-up and beak-up flight, were expressed also during the subjective day of (DD)dim. Birds exposed to LL retained similar patterns of activity to the 18L:6D condition for 3 days, after which they became arrhythmic. Behavioral observations of intense locomotor activity observed during the subjective night of LL revealed no beak-up and beak-up flight. Thus, the complete expression of migratory restlessness that includes beak-up and beak-up flight may not be regulated by a circadian oscillator but instigated by very low light intensity. Locomotor activity and associated daytime behaviors appear to be influenced by a circadian oscillator, given their persistent patterns under LL. Therefore, we suggest that the separate components of migratory behavior are regulated differentially by a circadian oscillator and ambient lighting conditions.
鸟类迁徙是一种季节性活动，在年度和每日基础上都需要精确的时间安排。随着越来越多的证据表明候鸟物种的日常活动存在内源性调节，我们测试了昼夜节律振荡器是否可能参与长途迁徙鸟类白顶雀（Zonotrichia leucophrys gambelii）的日常运动活动和特定行为的表达。我们之前的研究已经确定了在18小时光照：6小时黑暗（18L:6D）光周期下的白天和夜间行为模式。在两项独立试验中，处于春季迁徙生活史阶段的鸟类被置于持续昏暗光照（DD）dim和持续明亮光照LL条件下，同时收集运动活动和行为观察数据。在（DD）dim条件下，在18L:6D条件下观察到的包含活跃和静止成分的白天行为消失了，而迁徙不安这种强烈的夜间活动持续不间断达36.4小时。此外，通常局限于18L:6D黑暗阶段的迁徙不安的特定行为，即喙向上抬起和喙向上抬起飞行，在（DD）dim的主观白天也有表现。暴露于LL条件下的鸟类在3天内保持了与18L:6D条件下相似的活动模式，之后它们变得无节律。在LL的主观夜间观察到的强烈运动活动行为中没有发现喙向上抬起和喙向上抬起飞行。因此，包括喙向上抬起和喙向上抬起飞行的迁徙不安的完整表达可能不是由昼夜节律振荡器调节的，而是由非常低的光照强度引发的。鉴于运动活动和相关的白天行为在LL条件下的持续模式，可以看出它们似乎受昼夜节律振荡器的影响。因此，我们认为迁徙行为的不同组成部分受昼夜节律振荡器和环境光照条件的不同调节。
