Energetics and survival of birds in extreme environments

As northern climates changed towards those existing at present, bird taxa kept evolving forms adapted to the variety of high-latitude habitats - inland, coastal and alpine. These habitats are structurally simple and dominated by dramatic seasonality and permafrost. These adaptations are expressed in several seasonal and regional avifaunas which include the 20-25 resident bird species of the Siberian taiga, and some 15-45 typical summer visitors to hypoarctic, subalpine and tundra habitats. The survival strategies of birds in these extreme habitats are discussed in the light of experimental data and observations gathered during the seemingly most stressful periods of the birds' annual life cycle, namely mid-winter in north-eastern Asia and incubation on permafrost in upland tundra. Of the subarctic residents, only grouse utilise predictable browse foods, but have to cope with its low energy content. Winter survival in other taxa depends on utilising fall harvests and individual energy stores. In all cases, the energy utilisation in wintering birds appears to be minimised. In summer, non-resident birds treat their local resources in quite a different way with no evidence of direct energy limitation on reproduction, including incubation. There is little evidence of individual cost-minimisation strategies. Instead, local population-resource balances are regulated through a variety of social mechanisms.