Arid-dwelling mammals are exposed to extreme daily temperatures, which puts these mammals at risk of overheating and dehydration, particularly while active, these risks are increased as the body size is reduced. Consequently, these small mammals often show strict nocturnality, confining their locomotor activity to the dark period of the day. One such animal is the Lesser Egyptian Jerboa (Jaculus jaculus), which occurs in the hyper-arid central regions of the Arabian Peninsula. In this study, twelve male J. jaculus were subjected to different light regimes. All the animals exhibited entrainment of their activity to the dark phase of each respective light regime. However, unlike other small arid dwelling mammals, J. jaculus confined most of its activity during the last few hours of the night rather than the initial hours of the night, a pattern which is consistent even under constant DD conditions. The last few hours of the night correlate to the coolest experienced temperatures in summer in the wild and, therefore, the ideal time for a very small mammal to be active. Larger small mammals, which may be less at risk of overheating, can afford to be active during the warmer periods of the night, namely the initial hours.

生活在干旱地区的哺乳动物每天都暴露在极端的温度下，这使这些哺乳动物面临过热和脱水的风险，特别是在活动时，这些风险随着体型的减小而增加。因此，这些小型哺乳动物经常表现出严格的夜间活动，将它们的运动活动限制在白天的黑暗时期。其中一种动物是小埃及跳鼠（Jaculus jaculus），它生活在阿拉伯半岛极度干旱的中部地区。在这项研究中，十二只雄性 J. jaculus 接受了不同的光照条件。所有动物都表现出将其活动夹带至每个相应光照状态的黑暗阶段。然而，与其他小型干旱栖息哺乳动物不同，J. jaculus 将其大部分活动限制在夜间的最后几个小时，而不是夜间的最初几个小时，即使在恒定的 DD 条件下，这种模式也是一致的。夜晚的最后几个小时与夏季野外最凉爽的温度有关，因此，这是小型哺乳动物活动的理想时间。较大的小型哺乳动物可能不太容易过热，因此可以在夜间较温暖的时期（即最初的几个小时）活动。