Ornis Hungarica. vol.19. (2011) p.40-52.
Ivarmeghatározás biometriai adatok alapján – esettanulmány a csilpcsalpfüzikére
In the current study, we used statistical methods to sex Chiffchaffs breeding within the Carpathian basin by their wing and/or tail length measurements of adult birds collected between 1984 and 2007 by the Ócsa Bird Ringing Station Society, and explored the possibilities of further usage of obtained results. A total of 2902 individuals were included in the analyses (1574 from spring and 1328 from autumn). We applied model based clustering on the wing length, tail length and both measurements simultaneously to differentiate the sex groups. Clustering based on wing lengths proved to have the smallest uncertainty, however models using both measurements allowed a finer classification. The sex ratio was biased towards males in both seasons; on average 45:55% in spring, while 33:67% in autumn. Moreover, the ratio changed in favour of males during the 23 years of the study period. We found significant increase in wing length when not considering the sexes, however this was caused by the significant shift in the sex ratio towards males. In general, we can conclude that the sexes can be separated with high certainty based on biometric measurements in case of Chiffchaffs breeding within the Carpathian Basin. Possibly the bias in sex ratio of spring and autumn migration may be caused by protandry or protogyny; the different migration strategies of sexes. By incorporating the sexes, studies can avoid showing seemingly significant trends in biometric traits, like the increase in wing length over a moderately long time period.