Hypothalamic and colonic temperature were simultaneously measured in the calliope hummingbird (Stellula calliope). The vascular anatomy of the temporal region of these birds was also examined.
At air temperatures below 36°C, calliope hummingbirds regulated their body temperature between 35.6 and 40.6°C. At higher air temperatures, colonic temperature increased.
Brain temperature was lower than body temperature at high colonic temperatures (>39.5°C). The body-to-brain temperature difference in birds with high body temperatures averaged 0.73°C and remained relatively constant at all colonic temperatures above 39.5°C.
At body temperatures below 39.5°C, brain temperature of calliope hummingbirds exceeded colonic temperature by an average of 1.38°C. The possible explanations for this observation are discussed.
Calliope hummingbirds lack arete mirabile ophthalmicum, the countercurrent arterial-venous heat exchanger responsible for brain cooling in other birds.
Brain cooling in calliope hummingbirds apparently depends on heat exchange between arterial blood flowing to the brain, and cool venous blood returning from evaporative and convective surfaces at sites other than therete mirabile ophthalmicum.
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Burgoon, D.A., Kilgore, D.L. & Motta, P.J. Brain temperature in the calliope hummingbird (Stellula calliope): a species lacking arete mirabile ophthalmicum . J Comp Physiol B 157, 583–588 (1987). https://doi.org/10.1007/BF00700978
- Human Physiology
- Body Temperature
- Temperature Difference
- Heat Exchanger
- Temporal Region