Nestling sex ratios in the polygynously breeding Corn Bunting Miliaria calandra

We used a PCR-SSCP assay to sex 288 nestling Corn Buntings Milaria calandra from 113 clutches studied between 1988 and 1990 in the Western Isles, Scot land. In each year the sex ratio was not statistically different from 1:1. Brood sex ratios did not deviate significantly from the binomial distributi on when tested by robust randomisation tests. Although the effect was not s trong, the proportion of males in broods declined as the breeding season pr ogressed in 1989, although the opposite trend was observed in 1988 and 1990 . Overall, we found no effect of year, timing of breeding, levels of polygy ny, brood size or female size on brood sex ratios although several terms ha d significant interactions with year due to the effects of the data collect ed in 1989. Independently of brood size, the feeding rates of males, female s or both combined did not vary in relation to brood sex ratios. However, t he proportion of feeds provided by fathers was highest at male-biased brood s when brood size was small (1-3 young) but at female-biased broods when br ood size was large (4-5 young).