GREAT-TIT-HATCHLING SEX-RATIOS

The sex of Great Tit Parus major nestlings was determined using PCR RA PDs. Because this technique requires minute amounts of DNA, chicks cou ld be sampled soon (0-2d) after hatching, before any nestling mortalit y occurred. The proportion of males among 752 chicks hatching in 102 b roods (98.9% of those that hatched) increased with hatching date from 42.4% male in first broods (n=555 chicks) to 50.9% male in second broo ds (n=167). The proportion of males among hatchlings also decreased wi th increasing clutch size and increased with increasing hatching async hrony. These three variables are intercorrelated and it was not possib le to separate them statistically. Hatchling sex ratio was not correla ted with the age, weight or wing-length of either of the parents, broo d size at hatching or fledging, hatching or fledging success, mean chi ck weight, or position in the hatching sequence. The functional signif icance of the sex ratio variation found is unknown.