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In hot, arid environments, non-burrowing mammals are at risk of overheating and dehydration, so human-induced reduction in thermal cover may constitute a threat for their survival. We studied the daytime activity rhythm, habitat use, and space use of the beira (Dorcatragus megalotis), a threatened antelope living in arid hills of the Horn of Africa, where tree cover is shrinking because of logging, and overgrazing by livestock. During the cool season (Nov.-Mar.; mean midday temperature: 28.5 degrees C), beira did not particularly seek shade, and alternated in the course of the day between short phases of activity and rest (median duration in Dec.-Feb.: 57.5 and 42.5 min, respectively). In contrast, during the hot season (May-Sep.; mean midday temperature: 39.1 degrees C), beira often foraged in a hill’s shade, and midday resting phases were especially long (median duration in May-Jul.: 280 min) and spent in the shade of trees, or of rock shelters when available in the home range. Because of reduced diurnal movements when temperature was high, beira home ranges were smaller during the hot than during the cool season (mean +/- SE: 0.25 +/- 0.05 km(2) in May-Jul. vs 0.42 +/- 0.10 km(2) in Dec.-Feb.). Whatever the season, beira mainly used areas supporting trees. The obtained results suggest that the decrease of tree cover in the areas inhabited by the beira constitutes a threat for the species survival. (C) 2012 Elsevier Ltd. All rights reserved.