Abstract:
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.
