Metabolic rate and evaporative water loss of Mexican Spotted and Great Horned Owls

Abstract

We measured rates of oxygen consumption and evaporative water loss (EWL) of Mexican Spotted (Strix occidentalis lucida) and Great Horned (Bubo virginianus) owls in Arizona. Basal metabolic rate averaged 0.84 ccO₂ ^. g^{-1 .} h^-1 for the Spotted Owl and 0.59 ccO₂ ^. g^{-1 .} h^-1 for the Great Horned Owl, with apparent thermoneutral zones extending from 17.0-25.2°C for the Spotted Owl and 20.3-32.2°C for the Great Horned Owl. EWL increased exponentially with ambient temperature in both species, but the Great Horned Owl showed a greater ability to dissipate metabolic heat production at high temperatures than did the Spotted Owl. Body temperature of Spotted Owls was significantly higher above than below the upper critical temperature (25.2°C) whereas body temperature of Great Horned Owls did not differ significantly with ambient temperature. Gular flutter was first observed in Spotted Owls at 30°C and in Great Horned Owls at 37°C. The lower ability of the Spotted Owl to dissipate heat via evaporative cooling may partially explain its tendency to use habitats featuring cool microsites.

Citation

Ganey, Joseph L.; Balda, Russell P.; King, Rudy M. 1993. Metabolic rate and evaporative water loss of Mexican Spotted and Great Horned Owls. Wilson Bulletin 105 (4) 645-656