We studied the diurnal activity patterns of the African ice rat Otomys sloggetti robertsi, a murid rodent endemic to the harsh alpine and sub-alpine habitats of southern Africa. The taxon is poorly adapted physiologically to cold conditions, and we investigated whether the activity of free-living O. s. robertsi is modified by prevailing environmental conditions. O. s. robertsi displayed a bimodal diurnal activity profile in summer, retreating into underground burrows during the middle of the day when ambient temperatures and solar radiation levels were at their highest. In contrast, during winter, O. s. robertsi displayed a unimodal activity profile by spending most of the day foraging aboveground and extending its foraging bouts for about half an hour after sunset. More time was spent foraging than basking in winter compared to summer. Levels of foraging decreased and levels of basking increased during periods of snow cover, although runways beneath the snow could have provided access routes to foraging areas. O. s. robertsi activity is dictated by environmental conditions seasonally, time of the day, and the absence or presence of snow, and the taxon responds to these conditions by trading off between behaviors critical for meeting thermoregulatory requirements.