ИСТИНА

Many recent studies of bird acclimation have demonstrated the high phenotypic plasticity of their basal metabolic rate (BMR). It turned out that the BMR of birds is negatively associated with ambient temperature (Ta) and can quickly adapt to changes in Ta. In Vietnam, we compared different energetic characteristics of wild sedentary tropical birds and long-distant migrants from mid-latitudes who winter there. Despite the existence of migrants and residents in the tropics for several months under the same climatic conditions, the effect of phenotypic plasticity does not equalize their BMR. It remains higher in migrants (see Bushuev et al. in another our contribution at IOC 2022). In this study, we compared several species of tropical migrants and residents focusing on other parameters of the Scholander-Irving energy model. Distant migrants breed in colder areas, so at breeding sites they should have smaller value of lower critical temperature (Tlc) and a more gentle slope of the dependence of the standard metabolic rate (SMR) on Ta. We tested whether this difference persists in the tropics or is offset due the effect of phenotypic plasticity. We found no differences between migrants and residents in the SMR slope. Contrary to ecological interpretation of the Scholander-Irving model, in both groups this slope was gentler than that in birds living in mid-latitudes. On the other hand, the Tlc of migrants was shifted to lower temperatures compared to the residents of the tropics. Our preliminary data indicate that the thermoregulatory abilities of birds exhibit greater phenotypic plasticity compared to BMR.