Ornis Hungarica. vol.19. (2011) p.75-84.
Changes in abundance of Greenfinches (Carduelis chloris) at Ócsa Bird Ringing Station in winters of 1984–2007
Kovács Szilvia, Csörgő Tibor, Harnos Andrea, Nagy Krisztina
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The partially migrating bird species react rapidly to changing weather parameters:
they alter their migration phenology. To describe these changes we used the records of 6226 Greenfinches (Carduelis chloris) caught at feeders and ringed by a standard methodology in winters of 1984-2007. 246 was the number of local breeders in the wintering population. 638 birds were recaptured after more than 6 days. According to our results the number of caught birds is low both in extremely mild and in extremely frosty winters, consequently our study site (Ócsa) could be in the middle zone of the wintering area of the species. The colder the weather is, the more adult birds spend the winter in the Carpathian Basin. In the population of birds breeding and wintering at our study site the ratio of subdominant individuals – juvenile females – decreases, if the average amount of precipitation of the previous year was large.
In these years the survival rate of southern wintering birds could be larger therefore the rate of overwintering individuals decreases in the next generation of Carpathian Basin breeders. The reasons of observed changes could be results of physiological reactions of individuals to changing weather parameters or results of evolutionary adaptations.