Long-term observations (1991–2002) have shown that Hawfinches breed throughout the extensive Białowieża Forest; they are only slightly less numerous in the forest interior than at its edge. Population size, habitat and nest sites were studied in two plots in the species-optimal habitat (continuous oak-lime-hornbeam old-growth). The true breeding density there was 4.0–8.4, reaching as much as 15.2 p/10 ha in some years, while, according to the combined territory-mapping method for the same period, it was, on average, 5.8 pairs/10 ha in oak-lime-hornbeam, 3.3 pairs/10 ha in riparian ash-alder, but less than 0.5 pairs/10 ha in mixed coniferous-deciduous or young deciduous stands (marginal habitats for this species). Being among the most numerous species in the Białowieża Forest bird community, Hawfinches hold small nesting territories that are sometimes loosely grouped. Nests are built at an average height of 18.1 (7–34) m in the tree canopy. Hornbeams are the preferred tree species for nesting in the oak-lime-hornbeam stands (also clumps of mistletoe in the continental maple), while black alders in the riparian woodland. Originally, the Hawfinch must have been a species of old, high forests. Its recent nesting elsewhere — low in bushes or, preferably, along woodland edges — is likely to be a secondarily acquired trait; it could also be due to a bias — Hawfinch nests are more easily discovered in such localities.
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Vol. 40 • No. 2