Distorted Sex Ratio among Small Broods in a Declining Capercaillie Population

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Abstract
A declining capercaillie, T. urogallus L. population was studied between 1968 and 1978 in south Norway. Autumn brood sizes were small and varied between 3 phases of the population density change. Female chicks outnumbered male chicks by > 2 to 1. The deviation from a 1:1 sex ratio increased as broods became smaller, particularly when brood size decreased from 3-2. Sex-preferential mortality related to food quality was the most probable causal factor. The observed phenomenon may also have an adaptive significance.

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