Sex Does Not Affect Early Growth or Survival in Chicks of the Roseate Tern

-We sexed 327 Roseate Tern chicks (Sterna dougallii) at hatching and measured their growth during the first three days of life. These data on early growth 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 early growth or survival differed between males and females. This finding in a sexually monomorphic species is consistent with the hypothesis that the sex-biased chick mortality observed in sexually dimorphic species results from differential costs in chick-raising. Received 15 September 2000, accepted 10 October 2000.