Large-scale studies on population-level sex ratios are few, even though sex ratio is an important determinant of population viability and dynamics. Mechanisms driving large-scale sex ratio variation include spatially autocorrelated resources and scale differences in local versus global Fisherian feedback of the operational sex ratio. In this study, we reanalyze historic data on sex ratios based on 187,404 hunted subadult and adult red squirrels (Sciurus vulgaris) capturing spatial sex ratio variation in 50×50 km squares throughout Finland over a period of 8 years. Overall, sex ratio was slightly male biased (50.9%) and relatively more 50×50 km squares showed a bias toward males (19% of squares) compared to females (8% of squares). Sex ratio was spatially autocorrelated at distances up to 200 km and in some years showed a U-shaped pattern: regions that were in close proximity and those that were far apart had similar sex ratios, but regions in-between had opposite sex ratios. We found no evidence that food supply (spruce cone crop) drives regional red squirrel sex ratio. Our findings add to the scarce evidence that vertebrate sex ratios show spatial patterns over large scales.
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Vol. 97 • No. 3