Top predator and interference competition modify the occurrence and breeding success of a specialist species in a structurally complex forest environment

The three-toed woodpecker Picoides tridactylus favours structurally complex forest biotopes that are also preferred by its predators and competitors. Among them, the goshawk Accipiter gentilis is a top predator that may have a positive indirect effect on the woodpecker by its negative impact on other predators. We studied this predator—prey community in a forest-dominated area of 470 km2 in southern Finland in 1987—2005 by controlling goshawk occupancy and habitat changes. Goshawk affected densities of bird predators and hole-nesting species and locations of the nest sites of woodpeckers. Goshawk (+) and great spotted woodpecker Dendrocopos major (—) were significantly associated with density changes and breeding success of three-toed woodpecker. Positive influence of goshawk was correlated with landscape fragmentation that indicates that goshawk could decrease mammalian nest predation on three-toed woodpecker. Territory quality of three-toed woodpecker may be substantially modified by species interactions and be mediated to its population development.