Journal of Comparative Physiology B

, Volume 162, Issue 1, pp 74–84 | Cite as

Effect of temperature and humidity on evaporative water loss in Anna's hummingbird (Calypte anna)

  • Donald R. Powers


Evaporative water loss (EWL), oxygen concumption \(\dot V_{O_2 } \), 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 (ϱva) ranging from 20 to 37 °C and 2 to 27 g·m-3, respectively. The EWL decreased linearly with increasing ϱva at all temperatures. The slopes of least squares regression lines relating EWL to ϱva 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 ϱva 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 (\((\dot H_e /\dot H_m )\)) 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 \((\dot H_e /\dot H_m )\) 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).

Key words

Thermoregulation Water regulation Endothermy Climatic adaption Trochilidae 



basal metabolic rate


evaporative water loss

\(\dot H_e \)

percent of metabolic heat production dissipated by evaporation

\(\dot H_e \)

ambient water vapor density

\(\dot H_m \)

body surface water vapor density


resting metabolic rate




body temperature


dew-point temperature


thermoneutral zone


body surface temperature

\(\dot V_{co_{_2 } } \)

carbon dioxide production

\(\dot V_{O_2 } \)

oxygen consumption


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Copyright information

© Springer-Verlag 1992

Authors and Affiliations

  • Donald R. Powers
    • 1
  1. 1.Department of Avian SciencesUniversity of CaliforniaDavisUSA

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