Climate change and thermoregulation of big mammals in the field

Big mammals reproduce too slowly for them to be able to adapt genetically to current rapid climate change. Indeed, some big mammals alive in 2016 still could be alive at the 2050 climate tipping point. Whether big mammal species have the capacity to respond phenotypically to the current climate change is unknown, because techniques have not been available for experimental studies of responses of big mammals to climate change, especially long-term responses of big mammals in the field. We have developed techniques to measure body temperature at multiple sites, locomotor activity and thermoregulatory behaviour in free-living terrestrial mammals, for periods of more than a year, without human presence. We have applied those techniques to measure thermoregulatory responses of different species of free-living mammal in Africa, Australia, North America and the Middle East, with sizes between ground squirrels and elephants. Other researchers subsequently have applied similar techniques to study responses of free-living Alaskan bears, and European artiodactyls. We have discovered that some mammal species have the ability to reduce thermal loads, by well-controlled shade-seeking or by transferring foraging activity to the night. Some have latent physiological talents that reduce the consequences of inescapable thermal loads, including relaxation of homeothermy (which may be inevitable or implemented), and switching body cooling from evaporative mechanisms, which compromise body water balance, to non-evaporative cooling; in the southern hemisphere, aridity induced by climate change probably poses a bigger threat to mammal welfare than does increased temperature. Amongst the ungulate species so important in African ecology, and for livestock production, artiodactyl species appear to be more resilient to climate change than are perissodactyl species. Short episodes of intense exercise, for example cheetah hunts, do not appear to impose lethal thermal threats, even in hot environments. Potentially-lethal thermal threats do arise from fright-induced hyperthermia resulting from the presence of humans, and from starvation induced hypothermia; climate change will reduce food availability, especially for diet-selective mammal species. Unusually for a big mammal, the diet-selective aardvark, usually nocturnally-active, appears to use sun-basking to counteract starvation-induced hypothermia, often unsuccessfully. We currently are applying our techniques to free-living primates; knowledge about the thermoregulation of free-living non-human primate species, and therefore their likely responses to climate change, is particularly poor.