Energetic adaptations in wintering passerines
Small sedentary passerines have to face lower resource levels, shorter days and harsher climatic conditions as winter approaches. These factors get increasingly severe the longer to the north an individual spends the winter and may well set the limit to the northern range for many bird species. By studying the same species at different latitudes, we can evaluate how individuals use specific adaptations depending on the severity of weather and foraging conditions. Such adaptations include metabolic adjustments, use of nocturnal hypothermia and improved feather quality.