ИСТИНА

Basal metabolic rate (BMR) reflects the minimum energy expenditure of an animal to maintain fundamental physiological processes. Previous analysis of a global database by Jetz et al. (2008) has demonstrated that long-distance migrants have an increased BMR compared to non-migrants (residents). Aviary acclimation studies have revealed a considerable phenotypic plasticity in BMR: under the influence of low ambient temperatures (Ta), BMR of birds increased after a relatively short time. Since the proportion of migrants is much higher among species breeding in colder regions (high and temperate latitudes) compared to warmer regions (subtropical and tropical latitudes), the increased BMR in migrants was often attributed to a negative relationship between BMR and Ta. In our study, we performed a phylogenetically controlled analysis using two datasets: a global database of published avian BMRs from measurements on breeding grounds, and our own BMR measurements in birds from Vietnam (127 tropical sedentary species and 23 long-distance migrants on their wintering grounds). We took into account the effect of phylogenetic plasticity of BMR by including in the analysis the Ta that the birds experienced within the week preceding BMR measurements. We estimated different characteristics of Ta based on the information of the exact timing and location of BMR measurements from the original publications. In a phylogenetically controlled analysis of the global database, we showed that despite the strong temperature effect, the BMR of migrants was significantly higher than that of residents. In addition, we showed that although the climatic life conditions of migrants and residents in Vietnam were the same for several months, the BMR of the former was higher than that of the latter. We suggest that the high BMR of migratory birds reflects the high energetic cost of maintaining the physiological machinery required to perform long-distance flights.