Metabolic response to changes in temperature in northern wheatears from an arctic and a temperate populations
2013
Maggini, Ivan | Bairlein, Franz
Until recently it had been widely accepted that birds are energetically adapted to the latitude they inhabit, having an increased basal metabolic rate (BMR) at higher latitudes. Latterly, this general view has been questioned and the influence of phenotypic flexibility, due to factors such as habitat, life‐history or acclimatization has received increased attention. In particular, focus has been directed towards comparing species from arid and mesic habitats, but less attention has been given to species which breed in cold climates. We chose to study northern wheatears Oenanthe oenanthe from two populations at different latitudes (southern Norway, Iceland), but with similar life‐histories and habitat requirements throughout the year, in a common‐garden experiment. In order to assess true latitudinal trends in metabolic rate, we estimated the nocturnal resting metabolic rate (RMR) of northern wheatears from southern Norway and Iceland at different temperatures from 0° to 30°C. We found that Norwegian birds had overall lower metabolic rates than Icelandic birds, which were also slightly larger. This difference was not observed at 0°C, which might indicate that Icelandic birds might rely on better feather insulation reducing metabolic costs at very low temperatures. At temperatures above 10°C birds of both populations had constant metabolic values, indicating that their thermoneutral range almost completely covered the temperatures experienced during the breeding period. This study shows that the northern wheatear, which is one of only a few insectivorous long‐distance migratory songbirds occurring at such high latitudes, has evolved metabolic adaptations to life at cold temperatures which are endogenously determined.
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