The breeding performance of Hawfinches was studied during seven years (1991–98, except 1995) under conditions of an extensive close-to-pristine oak-lime-hornbeam forest in the Białowieża National Park, eastern Poland. Two 30–31.5 ha plots were regularly checked each year to find most nests present, usually observed since the period of their construction. Mean clutch size (5.27 ± 0.66, for best year — 5.5) finally produced small family size, owing to a partial loss, fledging and post-fledging mortality. Average breeding losses calculated traditional way were 72.8% (n = 202), mostly due to egg robbing, then predation on nestlings (three times less frequent), and, sporadically, adverse weather conditions at the moment of fledging. Nesting success (5.9–35.7%, 27.2% on average), strongly varying between years, is lower than in most Hawfinch populations from other (anthropogenic) habitats, being one of the lowest among temperate Passerines. In spite of low production of young the species remains numerous across deciduous stands of the Białowieża Forest, with its numbers even increasing since the 1980s. This large and dense population living in an apparently optimal habitat may, sporadically, be supported by influxes from other (anthropogenic?) sites.
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Vol. 47 • No. 1