DST-NRF Centre of Excellence at the FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Hatfield, Private Bag X20, Pretoria, 0028, South Africa.
South African Research Chair in Conservation Physiology, National Zoological Garden, South African National Biodiversity Institute, P.O. Box 754, Pretoria, 0001, South Africa.
J Comp Physiol B. 2019 Feb;189(1):131-141. doi: 10.1007/s00360-018-1190-1. Epub 2018 Nov 28.
Much recent work on avian physiological adaptation to desert environments has focused on larks (Passeriformes: Alaudidae). We tested the prediction that the threatened red lark (Calendulauda burra), a species restricted to very arid parts of South Africa and which is not known to drink, exhibits highly efficient evaporative cooling and makes pronounced use of facultative hyperthermia when exposed to high air temperatures (T). We also predicted that C. burra possesses similarly low basal metabolic rate (BMR) and total evaporative water loss (EWL) at moderate T as reported for species from the deserts of the Middle East. Rest-phase thermoregulation in C. burra was characterized by an unusually low lower critical limit of thermoneutrality at T = ~ 21 °C and a BMR of 0.317 ± 0.047 W, the lowest BMR relative to allometrically-expected values yet reported in any lark. During the diurnal active phase, red larks were able to tolerate T up to 50 °C, with the onset of panting occurring at T = 38 °C. Maximum EWL was 1.475 ± 0.107 g h at T = 50 °C, equivalent to 620% of minimum EWL at thermoneutrality. The maximum ratio of evaporative heat dissipation to metabolic heat production was 1.58, a value towards the lower end of the range reported for passerines. Our data support the prediction that C. burra shows metabolic traits similar to those of other larks inhabiting extremely arid climates, but not the notion that evaporative cooling at high T in this species is more efficient than in most passerines.
近期有关鸟类适应沙漠环境的生理学研究主要集中在百灵科（雀形目：百灵科）。我们验证了这样一种预测，即受到威胁的红百灵（Calendulauda burra），一种仅生活在南非极干旱地区且不饮水的物种，表现出高效的蒸发冷却，并在暴露于高温（T）时明显利用适应性体温升高。我们还预测，C. burra 与从中东沙漠中报道的物种一样，在中等 T 时具有相似的低基础代谢率（BMR）和总蒸发水损失（EWL）。C. burra 在休息时的体温调节表现出不寻常的低临界热中性温度下限，在 T = ~ 21°C 时为 21°C，BMR 为 0.317 ± 0.047 W，这是在任何百灵科动物中报告的相对代谢率预期的最低 BMR。在白天的活动期，红百灵能够耐受高达 50°C 的 T，当 T = 38°C 时开始喘气。在 T = 50°C 时，最大 EWL 为 1.475 ± 0.107 g h，相当于热中性时最小 EWL 的 620%。蒸发散热与代谢产热的最大比值为 1.58，这是雀形目动物报告的范围内的低值。我们的数据支持这样一种预测，即 C. burra 表现出与其他栖息在极端干旱气候中的百灵科鸟类相似的代谢特征，但不能证明该物种在高温下的蒸发冷却比大多数雀形目动物更有效。
