Does mist-netting provide reliable data to determine the sex and age ratios of migrating birds? A case study involving the Great Tit (Parus major) and the Blue Tit (Cyanistes caeruleus)

Nowakowski J.K., Chruściel J., Muś K.: Does mist-netting provide reliable data to determine the sex and age ratios of migrating birds? A case study involving the Great Tit (Parus major) and the Blue Tit (Cyanistes caeruleus). Ekologia (Bratislava), Vol. 32, No. 2, p. 173-185 , 2013.

Ringing results of tits caught at two stations on the Polish Baltic coast were used to check if mistnetting could be successfully used to analyse the composition of sex and age classes of migrating birds. Four hypotheses are discussed, describing the distribution of age and sex classes during migration, and the consequences these distributions might have for the catching results. We analysed records of 59 000 Blue Tits and more than 84 000 Great Tits that were caught and we found a similarity in the results of catches at stations 188 km apart, and a higher similarity among catching sites 0.5-16 km apart. These results proved that mist-netting provides reliable data on the sex and age structure of migrating flocks, and that these data can generally be interpreted as representative for at least the area in a radius of more than 10 km. The results also showed a migratory divide through the central part of the Polish Baltic coastline between irruptive Blue Tits in the west and regular partial migrants in the east. Great Tits showed no tendency for irruptions anywhere in the study area. A high correspondence in the age and sex ratio was found for Great Tits and Blue Tits, in particular where both species are regular migrants. We found that the ratios of females and immatures did not differ by more than 1% over many years of study in these areas.