Gerson A.R., Smith E.K., Smit B., McKechnie A.E., Wolf B.O.
Department of Biology, University of New Mexico, Albuquerque, NM, United States; Department of Zoology, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa; DST/NRF Centre of Excellence at the Percy FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield, South Africa
Gerson, A.R., Department of Biology, University of New Mexico, Albuquerque, NM, United States; Smith, E.K., Department of Biology, University of New Mexico, Albuquerque, NM, United States; Smit, B., Department of Zoology, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa; McKechnie, A.E., DST/NRF Centre of Excellence at the Percy FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield, South Africa; Wolf, B.O., Department of Biology, University of New Mexico, Albuquerque, NM, United States
Environmental temperatures that exceed body temperature (Tb) force endothermic animals to rely solely on evaporative cooling to dissipate heat. However, evaporative heat dissipation can be drastically reduced by environmental humidity, imposing a thermoregulatory challenge. The goal of this study was to investigate the effects of humidity on the thermoregulation of desert birds and to compare the sensitivity of cutaneous and respiratory evaporation to reduced vapor density gradients. Rates of evaporative water loss, metabolic rate, and Tb were measured in birds exposed to humidities ranging from ∼2 to 30 g H2O m−3 (0%-100% relative humidity at 30°C) at air temperatures between 44° and 56°C. In sociable weavers, a species that dissipates heat primarily through panting, rates of evaporative water loss were inhibited by as much as 36% by high humidity at 48°C, and these birds showed a high degree of hyperthermia. At lower temperatures (40°-44°C), evaporative water loss was largely unaffected by humidity in this species. In Namaqua doves, which primarily use cutaneous evaporation, increasing humidity reduced rates of evaporative water loss, but overall rates of water loss were lower than those observed in sociable weavers. Our data suggest that cutaneous evaporation is more efficient than panting, requiring less water to maintain Tb at a given temperature, but panting appears less sensitive to humidity over the air temperature range investigated here. © 2014 by The University of Chicago. All rights reserved.
air temperature; bird; body temperature; cooling; desert; environmental factor; evaporation; metabolism; relative humidity; thermoregulation; Animalia; Aves; Oena capensis; Philetarius socius; Water; animals; body temperature regulation; Columbidae; Hot Temperature; Humidity; Passeriformes; physiology; South Africa; Water Loss, Insensible; Animals; Body Temperature Regulation; Columbidae; Hot Temperature; Humidity; Passeriformes; South Africa; Water; Water Loss, Insensible