Pileated woodpecker nest and roost trees in Montana: links with old-growth and forest 'health'

摘要

The pileated woodpecker (Dryocopus pileatus) requires large trees for nesting, and its abandoned excavations are used by many birds and other small animals for nesting, roosting, hiding, and feeding. From 1973 through 1995, nest and roost trees of pileated woodpeckers were located in northwestern Montana forests dominated by western larch (Larix occidentalis) and Douglas-fir (Pseudotsuga menziesii). Nests (113 in 97 trees) were in western larch (n=52), ponderosa pine (Pinus ponderosa, n=18), blackcottonwood (Populus trichocarpa [P. balsamifera subsp. trichocarpa], n=15), trembling aspen (Populus tremuloides, n=7), western white pine (Pinus monticola, n=3), grand fir (Abies grandis, n=1), and Douglas-fir (n=1). Nest-tree diameter at breast heightaveraged 73 cm, and height averaged 29 m. Roost trees (n=40) were similar to nest trees, but had more cavity entrances and higher basal area of surrounding forest. Nest trees and roost trees typically were snags (81% and 78%, respectively) with broken tops (77% in both). Old-growth stands containing western larch were common nesting sites for pileated woodpeckers. Old-growth ponderosa pine, black cottonwood, and trembling aspen were locally important, but their distribution was more restricted. Comparedto other nest-tree species in Montana, undecayed larch wood is hard, making excavation difficult for woodpeckers. Heartwood decay, which softens the wood, becomes more prevalent as a forest matures and was characteristic of western larch nest trees. Inthe northern Rocky Mountains, the pileated woodpecker has been used too broadly and simplistically as a management indicator of old growth. A more realistic strategy would nurture western larch old growth, defined ecologically, as an indicator of high-quality nesting habitat for pileated woodpeckers. Large trees, logs, snags, carpenter ants (Camponotus spp.), and heartwood decay are intrinsic components of 'healthy' old growth that sustains pileated woodpeckers.