Passive Acoustic Monitoring within the Northwest Forest Plan Area: 2024 Annual Report

Abstract

Passive acoustic monitoring (PAM) has become the primary framework for assessing the status, distribution, and habitat associations of forest-dependent wildlife under the Northwest Forest Plan (NWFP). In 2024, the NWFP PAM program continued to operate as a fully integrated, range-wide monitoring network, building on deployments initiated in 2018 and now conducting surveys across approximately 24 million acres of federal land. Using a randomized 2+20% sampling design, more than 4,000 autonomous recording units generated over 2 million hours of acoustic data analyzed with convolutional neural networks, enabling statistically rigorous inference at regional and range-wide scales. This report summarizes 2024 field efforts and analytical advancements in the context of recent peer-reviewed and in-progress studies. Updated analyses confirm persistent, low occupancy of northern spotted owls (Strix occidentalis caurina), with detections concentrated in the Klamath Mountains and southern Cascades, consistent with long-term demographic declines. Range-wide models of barred owl (Strix varia) landscape use continue to show high occupancy across much of the NWFP area, reinforcing competitive displacement as the dominant driver of spotted owl range contraction. The PAM network also advanced monitoring of marbled murrelets (Brachyramphus marmoratus), with 2024 results supporting PAM as a cost-efficient alternative to traditional audio-visual surveys for assessing inland nesting habitat use in coastal forests. Beyond focal species, the program increasingly supports multi-taxa biodiversity monitoring through bioacoustic bycatch and soundscape analyses, linking species occurrence, habitat condition, and disturbance dynamics. Collectively, 2024 results demonstrate that PAM has reached operational maturity as the cornerstone of Phase II NWFP effectiveness monitoring. Sustaining adequate sampling effort and field capacity remains a challenge but essential, as reduced deployment intensity would increase uncertainty and weaken inference. Continued investment in PAM infrastructure and expertise is critical for informing adaptive management, supporting sustainable timber harvest, and evaluating ecosystem resilience under changing disturbance regimes.