VARIATION IN SEX-RATIOS OF OFFSPRING IN WILD BUSHY-TAILED WOODRATS

We investigated the effects of maternal weight and age and density of breeding females on sex ratio (percentage of males) in litters of wild bushy-tailed woodrats (Neotoma cinerea), a sexually dimorphic rodent. Sex ratios in full-sized litters (i.e., those that had not likely exp erienced mortality during gestation or lactation) were unaffected by e xperimentally reduced densities of females, nor did they differ betwee n litters born to yearling and adult (greater than or equal to 2 years ) mothers. However, sex ratios in litters were strongly correlated (R = 0.71, P = 0.0001) with prebreeding body weight in adult mothers, sug gesting that adult woodrats adjust sex ratios in litters at conception or early gestation in relation to maternal condition. Although yearli ng mothers did not appear to adjust prebirth sex ratios, postbirth los s was more strongly male-biased in litters born to yearling mothers th an in those born to adults, and we suggest that yearlings may adjust s ex ratios during the investment periof from birth to weaning.