Effects of fire and salvage logging on the cavity-nesting bird community in northwestern Montana

Caton, Elaine

I studied the effects of a large, stand-replacement fire on a cavity-nesting bird community in northwestern Montana for five years, starting two years post fire. I compared bird abundances in burned and unburned mid-elevation coniferous forests, and investigated the importance of nest-site and foraging-site availability in explaining differences in abundance. Differences in abundance appeared to be due largely to differences in foraging opportunities, rather than to nest-site availability. Timber-drilling woodpeckers, aerial insectivores, and ground foragers were more abundant in post-fire habitat, whereas gleaners were less abundant. Pairs of species drawn from the same foraging guild were significantly more similar in abundance patterns than pairs drawn from different guilds, but species with similar nest sites did not show similar patterns of abundance. I recorded characteristics of sites used for foraging and nesting in the post-fire forest. Use of sites appeared to be determined by presence of foraging sites as well as nest-tree availability. Woodpeckers foraged on large larch, Douglas-fir, and lodgepole pines in stands with basal areas greater than expected based on availability. Correspondingly, nests were placed more often than expected in stands of high basal area and large-diameter trees. Nests were predominantly in large, broken-top aspen. I compared habitat and bird abundances between salvage logged and unlogged post-fire habitat. Bird abundances and nest densities were lower in post-fire forest stands that were logged, and fewer sites in logged stands were suitable for nesting. Within logged areas, birds nested in sites most similar to nest sites in unlogged habitat. Tree-foraging cavity nesters were less abundant in clearcut stands than in partially logged stands. Variation in forest stands around nests rather than in characteristics of nest trees seemed to best explain this difference in abundance. Fire maintains cavity nester diversity by providing plentiful foraging and nesting sites. Management actions that address only nest tree provisions will fall short of providing for all community members. Fire-created habitats that undergo little or no post-fire logging may become refugia for species facing rapidly dwindling sources of standing dead wood.