Effect of temperature and humidity on evaporative water loss in Anna's hummingbird (Calypte anna) |
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Authors: | Donald R Powers |
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Institution: | (1) Department of Avian Sciences, University of California, 95616 Davis, California, USA;(2) Present address: Department of Biology, George Fox College, 97 132 Newberg, Oregon, USA |
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Abstract: | Summary Evaporative water loss (EWL), oxygen concumption
, and body temperature (Tb) of Anna's Hummingbirds (Calypte anna; ca. 4.5g) were measured at combinations of ambient temperature (Ta) and water vapor density (va) ranging from 20 to 37 °C and 2 to 27 g·m-3, respectively. The EWL decreased linearly with increasing va at all temperatures. The slopes of least squares regression lines relating EWL to va at different temperatures were not significantly different and averaged-0.50 mg H2O·m-3·g-2·h-1 (range:-0.39 to-0.61). Increased va restricted EWL in C. anna more than has been reported for other endotherms in dry air. The percent of metabolic heat production dissipated by evaporation (
) was lower than that of other birds in dry air, but higher than that for other birds at high humidity when Ta 33 °C. When Ta>33 °C the effect of humidity on
was similar to that in other birds. Calypte anna might become slightly hyperthermic at Ta>37 °C, which could augment heat transfer by increasing the Tb-Ta gradient. Body temperature for C. anna in this study was 43 °C (intramuscular) at Tas between 25 and 35 °C, which is above average for birds. It is estimated that field EWL is less than 30% of daily water loss in C. anna under mild temperature conditions (<35 °C).Abbreviations BMR
basal metabolic rate
- EWL
evaporative water loss
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percent of metabolic heat production dissipated by evaporation
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ambient water vapor density
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body surface water vapor density
- RMR
resting metabolic rate
- Ta
ambient-temperature
- Tb
body temperature
- Td
dew-point temperature
- TNZ
thermoneutral zone
- Ts
body surface temperature
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carbon dioxide production
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oxygen consumption |
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Keywords: | Thermoregulation Water regulation Endothermy Climatic adaption Trochilidae |
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