Predictors of habitat use and nesting success for two sympatric species of boreal woodpeckers in an unburned, managed forest landscape

Abstract

Forest harvesting reduces mean stand age and dead wood amount. Among species dependent upon older forests and dead wood, primary excavators such as woodpeckers play an important ecological role by providing cavities for many other species. Conservation of these species thus requires striking a balance between timber harvesting and dead wood supply, especially under moderate natural disturbance regimes. In this study, we quantified habitat use in two closely-related, sympatric species: Black-backed (Picoides arcticus) and American Three-toed (P. dorsalis) Woodpecker, in the highlands of northern New Brunswick, Canada. Natural fires are rare in this ecoregion and forest harvesting is the main agent of landscape change, along with infrequent outbreaks of spruce budworm (Choristoneura fumiferana). Based on its habitat use patterns in other ecoregions, we hypothesized that Black-backed Woodpecker would select nest sites in mature coniferous forest stands and we expected that it would achieve a higher nest survival rate in forest stands than within, or at the edge of, cutblocks. Owing to sample size limitations for American Three-toed Woodpecker, statistical analyses were restricted to its occurrence patterns. Both species co-occurred, and there was no difference in detectability following conspecific and heterospecific playbacks. Contrary to our prediction, Black-backed Woodpecker selected nest sites with higher proportions of recently cut areas within 50 m than at randomly selected sites. Black-backed Woodpecker selected cutblocks for nesting when suitable snags were available and mature forest stands were present nearby as foraging habitat. For the species to persist in this landscape, the supply of snags must be continuous and forest stands must be sufficiently mature to host saproxylic insects.