Journal
JOURNAL OF COMPARATIVE PHYSIOLOGY B-BIOCHEMICAL SYSTEMS AND ENVIRONMENTAL PHYSIOLOGY
Volume 189, Issue 1, Pages 131-141Publisher
SPRINGER HEIDELBERG
DOI: 10.1007/s00360-018-1190-1
Keywords
Alaudidae; Basal metabolic rate; Body temperature; Calendulauda burra; Evaporative water loss; Heat tolerance
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Funding
- DST-NRF Centre of Excellence at the FitzPatrick Institute
- National Research Foundation of South Africa [110506]
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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-a). We also predicted that C. burra possesses similarly low basal metabolic rate (BMR) and total evaporative water loss (EWL) at moderate T-a 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-a=21 degrees C and a BMR of 0.317 +/- 0.047W, 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-a up to 50 degrees C, with the onset of panting occurring at T-a = 38 degrees C. Maximum EWL was 1.475 +/- 0.107g h(-1) at T-a = 50 degrees 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-a in this species is more efficient than in most passerines.
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