DIFFERENTIAL WINTERING AND SURVIVAL RATES OF AGE AND SEX GROUPS IN SOME SPECIES OF FINCHES

The data of trapping and ringing of chaffinches (Fringilla coelebs), b ramblings (F. montifringilla) and siskins (Carduelis spinus) migrating through Courish Spit of the Baltic Sea in 1957-1991 were used to dete rmine the winter distribution and survival rates of sex and age groups . No differences in the directions of migrations were found between se x and age groups of all three species. No significant difference in th e distance of migrations were found between the groups of siskins. The females of chaffinch and brambling migrate farther to the south than males, and among males adults migrate farther to the south than immatu re individuals. No significant differences were found in the annual su rvival rates between males and females and between adult and immature finches in all three species, although the survival of males was somew hat higher than that of females and the survival of adults was somewha t higher than that of immature birds. These results are discussed taki ng into account three hypotheses suggested to explain the causes of di fferential migration. None of these hypotheses can explain, why adult males migrate farther to the south than immature ones. The hypothesis is suggested, that the wintering in rigorous climate permits the immat ure finches to avoid overpopulation and severe competition.