Avian Conservation Bioacoustics in Human-modified Landscapes: Community Responses to Forest Management and Riparian Urbanization in the Pacific Northwest

Abstract

The global loss of biodiversity is among the most central environmental challenges of the 21st century, and understanding the effects of land-use change and resource management on forest and riparian ecosystems is critical for the conservation of wildlife and ecosystem functions. Populations of many avian species in the Pacific Northwest have declined substantially over the past half century due to a legacy of habitat loss and degradation through forest management and urban development. These trends continue today despite the designation of late-successional reserves and general stability of early-seral habitat following the passage of the Northwest Forest Plan in 1994, and the increasing adoption of compact urban growth strategies and riparian protections––initiatives that have revolutionized land-use and resource management in the region. This points to an urgent need to better understand the processes that generate and maintain avian biodiversity and inform management strategies to ensure ecosystem integrity amid the ongoing biodiversity crisis. Several practical challenges and knowledge gaps limit our current understanding of the relationships between forest and riparian management and avian communities. First, managers lack robust monitoring solutions that can operate at large spatiotemporal scales, and the promise of leveraging pre-trained bioacoustic classifiers with passive acoustic monitoring as an accessible and scalable method for rapid ecosystem surveillance remains unfulfilled due to poor generalization of classifiers in applied biodiversity surveys. Second, integrated forest management aims to balance biodiversity conservation with timber production and ecosystem service objectives, but the response of bird communities to habitat created through integrated forest management remains poorly understood, and uncertainties remain regarding the relative conservation value and ecological function of the developmental stages that constitute managed forest landscapes. Third, declines in insectivorous bird populations are attributed in part to parallel reductions in riparian habitat and the availability of aquatic prey, however, it remains unknown how urbanization alters aquatic subsidies and how these changes propagate to avian consumers, limiting our ability to anticipate future urbanization impacts and inform cross-boundary mitigation strategies. I address these challenges by applying novel methods in passive acoustic monitoring, machine learning, and quantitative community ecology to enable the investigation of avian community responses to forest management and riparian urbanization in the Pacific Northwest. My first chapter demonstrates the use of a few-shot transfer learning approach to efficiently adapt a pre-trained bioacoustic classifier to a new domain with minimal local training data. I present an open-source workflow with guidelines for evaluating performance with ecologically meaningful metrics and training a model to improve performance for existing species and to add additional species or sounds of interest. In my second chapter, I employ a custom bioacoustic classifier to survey breeding bird communities across a mosaic of forest developmental stages maintained by management in the Olympic Experimental State Forest, Washington. By leveraging multi-species occupancy models and multivariate analyses of community composition, I demonstrate the irreplaceable conservation value of mature primary forests and early-seral habitat and explore the importance of landscape management strategies that integrate both late-successional reserves and structurally enriched managed stands. Finally, in my third chapter I examine how aquatic insect communities, riparian vegetation, and urban land cover influence breeding bird assemblages across streams spanning an urbanization gradient in the Seattle metropolitan area. I use multi-species occupancy and structural equation modeling to reveal strong associations between stream biotic integrity and the richness of insectivore and migrant guilds, and report that the protection and restoration of riparian vegetation at both local and landscape scales may be necessary to maintain present-day avian richness levels in the face of projected urban expansion throughout the remainder of the century. Collectively, this research demonstrates the value of conservation bioacoustics for monitoring avian communities in human-modified landscapes and informing management strategies to protect avian biodiversity and ecosystem functions amidst continuing population declines.