In terms of their energy needs, the maintenance costs of individual birds while in Africa must be considerably less than on their Eurasian breeding grounds, as a result of two independent factors. The greater warmth in Africa reduces the intake of food needed to maintain body temperature, and the birds are less active in Africa because they carry none of the stresses associated with breeding, having only themselves to feed. On the basis of information available at the time, Moreau (1972) calculated that the daily maintenance needs of individual birds amount to roughly 60%, on average, of what they are on their breeding grounds. The mean temperature increase from breeding to wintering areas of 50 species of migrants was calculated by Moreau (1972) at over 6°C. Extremes were provided by tundranesting species which experienced July temperatures of 5-10°C, and then migrated to tropical Africa, with January temperatures of around 20-30°C.
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