The response of songbird assemblages to commercial thinning is likely to change as vegetation develops over time after thinning. The influence of thinning intensity and pattern on the timing of transitions in bird community composition following thinning is of interest to managers when a goal is to maintain diversity and accelerate the development of late-seral forest structure. We investigated changes in the composition of songbird assemblages and density of individual species from 2 years before to 12 years after experimental thinning of 40-year-old stands dominated by Douglas-fir (Pseudotsuga menziesii) in the Oregon Cascades. Species richness, and density for five species and the neotropical migrant group were greater in thinned than in unthinned control stands over all post-treatment years of the study. Similarly, three species maintained a negative response to thinning over the post-treatment period. The initial positive influence of thinning was no longer in evidence a decade after harvest for five species. Of seven species with an initial negative response to thinning, three indicated recovery towards pre-treatment densities by the end of the most recent post-treatment survey. Our study is one of the first to document long-term effects of commercial thinning on forest songbird assemblages in the Pacific Northwest.