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1 December 2016 Blackcaps Sylvia atricapilla on Migration: A Link between Long-Term Population Trends and Migratory Behaviour Revealed by the Changes in Wing Length
Agnieszka Ożarowska, Grzegorz Zaniewicz, Włodzimierz Meissner
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Abstract

Recent climate change has a major impact on the sizes and distribution of bird populations, the phenology of their breeding/migration and migratory behaviour (migration distance, migration strategy). We documented changes in the numbers of juvenile Blackcaps migrating in autumn through the S Baltic that were paralleled by changes in wing length of captured individuals during a 43-year study period (1967–2009). We suggest that the observed trends may indicate changing population composition of migrating birds. In the Blackcap, wing length distinguishes among different populations and increases with increasing migration distance of a given population. Available published data show that long-distance and short-distance Blackcaps pass the study region. Hence, we assumed that shorter-winged birds are short-distance migrants wintering in the southern Europe, and that longer-winged individuals are long-distance migrants wintering in the sub-Saharan region. It seems that in 1967–1980 most Blackcap populations declined, but, as wing length slightly increased, the rate of this decline has been higher in the shorter-winged/short-distance Blackcaps. Over the subsequent 24 years alongside with rapidly growing numbers of birds, we noted a remarkable decrease in wing length. This indicates a pronounced increase in the number of short-distance individuals compared to long-distance migrants. Both groups may benefit from improved conditions at their breeding grounds, but the shorter migration route and favourable conditions at wintering sites north of Sahara could favour short-distance migrants over the longer distance and longer-winged Blackcaps.

Agnieszka Ożarowska, Grzegorz Zaniewicz, and Włodzimierz Meissner "Blackcaps Sylvia atricapilla on Migration: A Link between Long-Term Population Trends and Migratory Behaviour Revealed by the Changes in Wing Length," Acta Ornithologica 51(2), 211-219, (1 December 2016). https://doi.org/10.3161/00016454AO2016.51.2.007
Received: 1 November 2015; Accepted: 1 December 2016; Published: 1 December 2016
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