Abstract
The study is based on own nest-card material from a mountain area in northern Finnish Lapland, where bird populations fluctuate greatly between years. Fifteen passerines were included in the analysis. Of these only one species (Anthus pratensis) had a larger average clutch size in northern Lapland than further south. It is suggested, in contrast to some earlier studies, that in harsh (or unstable, variable, unpredictable) physical conditions avian clutch size will be reduced. Apparently there is a limit to the reproductive capacity of females: they cannot afford to spend more than a limited amount of energy on reproduction when conditions are very unfavourable. The evolutionary implications of a low reproductive rate are discussed in relation to three theoretical life-history models (bet-hedging, stress-tolerant strategy, and adversity strategy), which all emphasize risk-avoidance in harsh environments.
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