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Deserts represent challenging, energy restricted environments for small mammals, but offer ample exposure to sunlight that might be used for energy saving during basking. The Succulent Karoo desert in southern Africa is a seasonal environment with cold moist winters, followed by maximum food availability in spring and dry hot summers with food shortage. The striped mouse (Rhabdomys pumilio) from the Succulent Karoo desert is diurnal and its activity is influenced by photoperiod in captivity. However, in contrast to standardized laboratory conditions, it can be expected that several factors other than photoperiod influence its activity pattern in the field. We expected that striped mice behave in a way that indicates that they use basking to passively warm up and thus reduce endogenous energy expenditure. We studied activity and basking patterns in 56 social groups of striped mice for a period of 4 yr, comprising 1534 observation sessions at their nests. Mice generally started activity around the time the sun illuminated their nest and terminated activity when their nest was no longer sunlit, i.e. they were strictly diurnal. The onset of activity was delayed on days when ambient temperature was colder and when group sizes were smaller. During the breeding season when food availability was high, striped mice usually left the nest before it was sunlit without basking. Outside the breeding season, they emerged and basked in front of nests mainly after nests were sunlit. These findings concur with the view that striped mice trade-off between active energy gain via foraging and passive energy acquisition by sun basking.