Survival to first breeding is not sex-specific in the Coal Tit (Parus ater)

Differential survival of males and females affects the structure and dynamics of avian populations, but studying sex-specific survival rates is difficult. This is especially true for offspring if the period between hatching and first breeding is considered. Under certain conditions, however, the determination of offspring sex ratio, recruitment and dispersal may help in the investigation of sex-specific survival rates to the age of first breeding. Applying a molecular technique we sexed a large sample of Coal Tit (Parus ater) nestlings from a nest box population in a coniferous forest near Lingen/Emsland (Lower Saxony, Germany). The study covered a period of two years and included first and second broods. We found that the sex ratio did not deviate from unity. Through capturing breeding adults in the second year, we were able to examine local recruitment rates and natal dispersal distances of male and female offspring. The sexes differed significantly neither in recruitment probability, which was generally high, nor in dispersal distance, which was generally low. Our results indicate that there is no difference in the survival rate of male and female Coal Tits during their first year of life. The relevance of our findings are discussed with regard to the characteristics of the study population.

Verena C. J. Dietrich, Tim Schmoll, Wolfgang Winkel and Thomas Lubjuhn, J. Ornithol. 144, 148-156 (2003)