Sex does not affect early growth or survival in chicks of the Roseate Tern

We sexed 327 Roseate Tem chicks (Srerna dougallii at hatching and measured their growth during the first three days of life. These data on early growt h predict their survival to fledging with high confidence (97% for A-chicks and 83% for B-chicks), using a discriminant function derived in an earlier study. After controlling for other factors, there was no evidence that ear ly growth or survival differed between males and females. This finding in a sexually monomorphic species is consistent with the hypothesis that the se x-biased chick mortality observed in sexually dimorphic species results fro m differential costs in chick-raising.