Lessons from long-term hole-nester studies in a primeval temperate forest

Nonexcavators (secondary hole-nesters) are birds that critically depend on holes for nesting and roosting; the absence of holes renders habitat uninhabitable to them. In man-managed woods, their populations are known to increase with the provision of nest-boxes, suggesting that the birds are limited by shortage of holes and must compete for them. I use 30 years of observations in the last fragments of primeval temperate forest of lowland Europe (Bialowieza National Park, eastern Poland) to test these assumptions. They show that, in primeval forest conditions, (1) birds do not face a shortage of holes, (2) competition for nest sites is of minor importance, (3) woodpeckers are not keystone hole providers, and (4) nonexcavated holes provide safer nest sites than excavated holes. The Bialowieza results are compared with studies from primeval forests on other continents. I conclude that in primeval forest conditions, hole-nesting nonexcavator birds are not, as a rule, nest-site-limited.