Assessing the effectiveness of a forest Habitat Conservation Plan for a threatened seabird, the marbled murrelet

Habitat Conservation Plans (HCPs) commonly facilitate habitat conservation on private land in the United States, yet the effectiveness of individual HCPs is rarely evaluated. Here, we assess the effectiveness of a high-profile HCP created by a lumber company to protect old-growth forest used for breeding by Marbled Murrelets (Brachyramphus marmoratus) on private land. We used 17 years of HCP-monitoring data to compare trends in murrelet occupancy and inland counts between private HCP areas and public reference areas over time. Based on occupancy models applied to audio-visual survey data, average occupancy was higher in public reference areas (0.85; 85% CI: 0.79-0.90) than in private HCP areas (0.46; 85% CI: 0.38-0.54). Numerically, trends in occupancy were slightly positive in public areas (λ=1.01; 85% CI: 0.94-1.08) and slightly negative in private areas (λ=0.97; 85% CI: 0.87-1.06), but confidence intervals did not preclude stable occupancy on both ownerships. Based on generalized lin...