Cutaneous and respiratory water loss in larks from arid and mesic environments

Birds from deserts generally have lower total evaporative water loss (TEWL), the sum of cutaneous (CWL) and respiratory water loss (RWL), than species from mesic areas. We investigated the role of CWL and RWL as a function of air temperature (T-a) in hoopoe larks (Alaemon alaudipes) and Dunn's larks (Eremalauda dunni) from the Arabian Desert and skylarks (Alauda arvensis) and woodlarks (Lullula arborea) from temperate mesic grasslands. The proportional contribution of CWL to TEWL in all larks at moderate T-a ranged from 50% to 70%. At high T-a (40degrees+/-45degreesC), larks enhanced CWL by only 45%-78% and relied on an increase in RWL by 676%-2,733% for evaporative cooling. Surface-specific CWL at 25degreesC was 29% lower in the arid-zone species than in the mesic larks. When acclimated to constant T-a, 15degreesC-acclimated hoopoe larks increased CWL by 22% compared with 35degreesC-acclimated birds, but the other species did not change CWL. This study is consistent with the hypothesis that larks from deserts have a reduced CWL at moderate and low T-a but provided no support for the hypothesis that at high T-a larks from arid regions rely more on CWL than larks from mesic environments. Interspecific differences in CWL cannot be attributed to acclimation to environmental temperature and are possibly the result of genetic differences due to natural selection or of phenotypically plastic responses to divergent environments during ontogeny.