Offspring sex ratio variation in the European badger Meles meles

The sex ratio of post-emergence offspring of the European badger Meles meles in Wytham Woods, Oxfordshire, UK did not differ significantly from 50% between 1987 and 2001. Insofar as male offspring are more costly to rear successfully, mothers optimized cub productivity with regard to the level of resources that they could invest. When females had a relatively high index of body condition, they implanted early; when implantation was early, the cub sex ratio was male biased. Additionally, years with a male-biased cub sex ratio coincided with a significantly larger cub cohort. These results do not support the local resource competition hypothesis, which proposes that in years when female body condition is poor, females should lower competition for local resources by producing the dispersing sex, i.e., males. The potential mechanisms by which offspring sex ratios may be skewed are discussed. Overall, it appears that bias in the cub sex ratio may result from a combination of adaptive parental strategies, differential infanticide by individuals other than the mother, and differential fetal mortality between the sexes.