City of Seattle, Seattle Public Utilities, Marbled Murrelet Baseline Surveys 2005-2007, Cedar River Municipal Watershed, King County, WA

From 2005 to 2007, Seattle Public Utilities (SPU) hired consultants to use ornithological radar and protocol audio-visual (AV) surveys to establish baseline information on the distribution and abundance of Marbled Murrelets (Brachyramphus marmoratus) in the Cedar River Municipal Watershed (CRMW), Washington. Across the three years, radar surveys were conducted on 100 mornings at 18 sites, and AV surveys on 92 mornings at 12 sites. The study recorded murrelet targets via radar in all years, with 65 detections in 2005, 89 in 2006, and 25 in 2007. Mean daily landward radar counts ranged between 0 and 4 per morning, and did not differ significantly across years. Although overall radar counts were low, high day-to-day variability was observed (coefficients of variation from 130% to 173%). Monte Carlo simulations showed that with repeated surveys using the same methods, the monitoring program could detect an annual increase of 2–3% in Marbled Murrelet abundance over approximately 25–50 years. AV surveys confirmed murrelet occupancy at two sites: the Rex River in 2005 and the South Fork Cedar River in 2006. No murrelets were detected by AV in 2007, though radar data suggested low-level murrelet presence at several additional sub-basins. The findings indicate that Marbled Murrelets occur at low densities in the CRMW, likely limited by both high inland distance and relatively sparse old-growth forest structure suitable for nesting. The four radar stations established and resampled during the study provide an opportunity for long-term monitoring, offering sufficient power to detect changes in murrelet activity as ongoing forest restoration efforts in the CRMW progress.