干旱区生态环境知识资源中心

Nocturnally active birds roosting in exposed microsites can experience operative temperatures (T-e) that markedly differ from air temperature (T-a). Thus, quantifying T-e becomes important for accurately modeling energy and water balance. We measured T-e at roost and nest sites used by Rufous-cheeked Nightjars (Caprimulgus rufigena A. Smith, 1845) (mean body mass = 57.1 g) with three-dimensionally printed models covered with the plumage of a bird. Additionally, we estimated site-specific diurnal water requirements for evaporative cooling by integrating T-e and T-a profiles with evaporative water loss (EWL) data for Rufous-cheeked Nightjars. Between the hours of 12: 00 and 15: 00, representing maximum solar radiation, mean T-e at roost sites varied from 33.1 to 49.9 degrees C, whereas at the single nest site, Te averaged 51.4 degrees C. Mean diurnal EWL, estimated using T-e, ranged from 2.8 to 10.5 g among roosts, values 1.2- and 3.6-fold greater, respectively, than T-a estimates. At the nest site, total EWL estimated using T-e was 11.3 g, 4.0-fold greater than the corresponding estimate based on T-a. Consequently, Rufous-cheeked Nightjars can experience EWL potentially approaching their limits of dehydration tolerance. In the absence of microsite changes, climate change during the 21st century could perhaps create thermal conditions under which Rufous-cheeked Nightjars exceed dehydration tolerance limits before the onset of their nocturnal active phase.