We used a PCR-based molecular DNA sexing technique to sex European Sta
rling Sturnus vulgaris chicks from a nestbox colony at Wytham, Oxford,
UK. The nestling sex ratio among 350 one-week-old chicks from 108 bro
ods was significantly female-biased. There was no significant heteroge
neity in brood sex ratio. We found no significant correlations between
sex ratio and several environmental and parental variables, nor were
there any significant differences in egg dimensions or growth rates of
the sexes. Mortality, but not fledging sex ratio, was strongly correl
ated with hatching order, suggesting that the sex ratio imbalance was
not due to sex-biased chick mortality. The possibility that the overal
l sex ratio bias is dictated by maternal adjustment of the sex ratio i
s discussed.