LAUSR

Bats are the only mammals capable of powered flight. This characteristic has allowed them to successfully exploit many ecological niches inaccessible to other species of mammals and has led to an impressive taxonomical diversity. Bats thrive in virtually all kinds of habitats in the world, including deserts. It is almost counterintuitive that bats occupy desert environments. Powered flight requires wings with high surface areas relative to body mass, a high power output and high evaporative water loss rates; thus, bats would show physiological adjustments to be able to colonise habitats where the availability of food and drinking water is low. We collected data for 136 species of bats covering several physiological, morphological and behavioural variables, including mechanisms that have received little attention in the literature, such as conservation of plasma volume, faecal water loss or milk production, to describe a suite of physiological adaptations of arid‐zone bats. We found that arid‐zone bats are generally smaller than bats living in mesic environments. The typical arid‐zone bat is insectivorous; because of its diet, it shows a higher relative medullary thickness, and a higher urine osmolarity, traits that are also desirable to cope with aridity. This bat has a lower energy expenditure, a lower water loss, a higher physiological tolerance to roost in exposed sites and uses torpor at a higher ambient temperature than the mesic bat, characteristics that allow energy and water savings. In addition, the arid‐zone bat has a higher wing aspect ratio and a lower wing loading, which allows a higher efficiency for long‐distance flights to allow access to patchy resources. In summary, arid‐zone bats seem to show phenotypic adjustments going towards a reduction in both energy expenditure and water loss in such harsh environments, a strategy that has been reported in other groups of mammals subjected to similar selective pressures.