Potential thermoregulatory advantages of shade use by desert bighorn sheep

摘要

Ungulates in arid climates use a variety of mechanisms to cope with environmental conditions that can result in heat stress and dehydration. Use of shade during midday is common among desert ungulates of the southwestern United States. Desert bighorn sheep (Ovis canadensis mexicana) use both vegetation and caves as sources of thermal cover. We assessed potential thermoregulatory advantages of the use of vegetation and caves by desert bighorn sheep on the Cabeza Prieta National Wildlife Refuge, Arizona. Midday ambient temperatures in caves were an average of 6.9 ℃ (SE = 0.344) lower than control sites; ambient temperature under tree canopies was an average of 3.3 ℃ (SE = 0.950) below control sites. Caves provided higher quality shade than tree canopies; midday temperature in caves was an average of 3.4 ℃ (SE = 1.06) lower than under tree canopies. Potential thermal benefits of both caves and tree canopies increased with increasing daily high temperature. Behavioral adaptations function in combination with physiological and morphological mechanisms and are of critical importance for the maintenance of temperature and water balance. Short-term physiological and ecological performance is influenced by habitat selection and use of microhabitat; abiotic factors (e.g., ambient temperature) can ultimately influence animal fitness and the demography of animal populations.