LAUSR

1 Forest Biodiversity Research Network, Department of Forest Ecosystems and Society, Oregon State University, Corvallis, Oregon 2 Wildlife Research and Monitoring Section, Ontario Ministry of Natural Resources and Forestry, and Environmental and Life Sciences Graduate Program, Trent University, Peterborough, Ontario, Canada 3 Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon 4 Cooperative Institute for Marine Resources Studies, Oregon State University, Newport, Oregon 5 Department of Natural Resources Science, University of Rhode Island, Kingston, Rhode Island 6 US Department of Agriculture Forest Service, Rocky Mountain Research Station, Ogden, Utah 7 Department of Forest Ecosystems and Society, Oregon State University, Corvallis, Oregon 8 Current address of author James W. Rivers is Department of Forest Engineering, Resources, and Management, Oregon State University, Corvallis, Oregon Abstract Theory predicts that species requiring multiple habitat types simultaneously should have heightened sensitivity to anthropogenic pressures, yet tests of this prediction are especially rare. We tested whether breeding site occupancy of the threatened marbled murrelet (Brachyramphus marmoratus) was driven by the synergistic effects of nesting habitat loss in forests, and changing ocean conditions. We paired 70,700 murrelet surveys at 19,837 sites across 20 years from the Oregon Coast Range with annual data on the extent of old forest and biophysical ocean conditions. Dynamic occupancy models indicated that local murrelet colonization rates were strongly reduced during warm ocean conditions with low prey availability. Landscapes that contained more old forest and were closer to the ocean showed reduced rates of local extinction. Given predictions of accelerated ocean warming and increased global timber demand, our results suggest murreletsmay continue to be imperiled by deterioration of the two habitats upon which they depend.