King penguins (Aptenodytes patagonicus) may fast for up to 30 days during their breeding period. As such extended fasting may affect the relationship between the rate of O(2) consumption (Vo(2)) and heart rate (f(H)), five male king penguins were exercised at various speeds on repeated occasions during a fasting period of 24-31 days. In addition, Vo(2) and f(H) were measured in the same animals during rest in cold air and water (4 degrees C). Vo(2) and f(H) at rest and Vo(2) during exercise decreased with fasting. There was a significant relation between Vo(2) and f(H) (r(2) = 0.56) that was improved by including speed, body mass (M(b)), number of days fasting (t), and a cross term between f(H) and t (r(2) = 0.92). It was concluded that there was a significant change in the Vo(2)-f(H) relationship with fasting during exercise. As t is measurable in the field and was shown to be significant and, therefore, a practical covariate, a regression equation for use when birds are ashore was obtained by removing speed and M(b). When this equation was used, predicted Vo(2) was in good agreement with the observed data, with an overall error of 3.0%. There was no change in the Vo(2)-f(H) relationship in penguins at rest in water.
