Blackcap numbers, phenology and reproduction in a primeval forest--a 33-year study

Tomasz Wesołowski (1)

1 Department of Avian Ecology

Data on Blackcaps gathered in 1975-2007 in an old-growth primeval forest (Białowieża National Park, Poland) are analysed to see whether the species numbers, breeding phenology or reproduction showed any long-term trends. Neither the clutch size (mean 4.8) nor the nesting success (c. 38%) changed, but a number of directional changes during 33 years were observed. In comparison with the 1970s, in the twenty-first century, Blackcaps arrived over 2 weeks earlier, but advanced egg-laying by only 8 days. The breeding numbers increased threefold; they had been increasing slowly before 2000, but almost exponentially from 2001 onwards. The densities raised to c. 10 pairs/10 ha in luxuriant riverine habitats. Due to structural changes in the oak-hornbeam habitat, in the twenty-first century, Blackcaps situated nests lower and less frequently in conifers. The numerical increases were only partially accountable by structural changes in local habitats, but they were concordant with large-scale increases of Blackcaps across W Europe. It is hypothesised that the forest has recently been invaded by Blackcaps from strongly increasing, SW migrating, populations.

Mots clés: Timing of breeding; Clutch size; Nesting success; Nest site; Arrival date

Tomasz Wesołowski. Blackcap numbers, phenology and reproduction in a primeval forest--a 33-year study. Journal für Ornithologie = Journal of Ornithology, 2010, 152 (2), pp.319-329. ⟨10.1007/s10336-010-0585-x⟩. ⟨hal-00630273⟩