Video from GPS collars reveals factors influencing tracking performance and desert bighorn sheep use of thermal refugia

Caves provide cooler microclimates than surrounding landscapes and may function as thermal refuges for desert species. Desert bighorn sheep ( Ovis canadensis mexicana ) inhabit hot, arid environments, yet the timing and factors driving cave use remain poorly understood. We fitted 16 desert bighorn sheep (9 F; 7 M) with GPS collars, 9 (5 F; 4 M) of which had video capabilities, to investigate determinants of cave use and fix loss and to predict interannual trends. GPS fix loss peaked during the hottest months and times of day (18.7%), with caves accounting for most fix loss (85.3%). Cave use was predicted by temperature, humidity, solar radiation, and daylength, and increased nearly 17-fold as ambient temperatures rose from 30 °C to 40 °C. Cave use peaked at midday during June–August and was rare during cooler seasons and at night. Bighorn sheep selected caves on north-facing slopes in midsummer; however, most midday bedding sites were not in caves. These findings highlight the importance of favorable microclimates during extreme heat and reveal tradeoffs between thermoregulation and predation risk. We suggest wildlife managers consider constructing permanent waters near caves on open, north-facing slopes where thermal benefits are greatest, but risk is reduced. • Cave use increased 17-fold as temperatures rose from 30 °C to 40 °C. • Cave use peaked at midday during June–August. • Cave use was infrequent during cooler seasons and at night. • Bighorn sheep selected caves on north-facing slopes during July and August. • Caves were the primary feature influencing fix loss.