Abstract
A conservation goal of the Northwest Forest Plan (NWFP) is to stabilize and increase marbled murrelet (
Brachyramphus marmoratus) populations by maintaining and increasing nesting habitat. We monitored murrelet populations offshore of the NWFP area from 2000 to 2013 to estimate population size and trend at several spatial scales. At the conservationzone scale, 2013 population estimates ranged from 71 birds in Conservation Zone 5 (San Francisco Bay north to Shelter Cove, California) to 7,880 in Conservation Zone 3 (Coos Bay, Oregon north to the Columbia River). The 2013 estimate for the entire NWFP area was 19,700 (95-percent confidence interval: 15,400 to 23,900). We found strong evidence of linear population declines in Washington at the state scale (4.6-percent decline per year; 95-percent confidence interval: −7.5 to −1.5 percent), and for the two conservation zones within the state. We found no evidence of a declining trend in California or Oregon, and inconclusive evidence for a trend at the scale of the NWFP area. We monitored murrelet nesting habitat distribution and trend, using maximum entropy (Maxent) models. Results indicate about 2.5 million ac of potential nesting habitat within the NWFP area at the start of the NWFP (1993), with a substantial amount of this (41 percent) on nonfederal lands. We found net losses of about 2 percent of habitat on federal lands and about 27 percent on nonfederal lands between 1993 and 2012. Fire was the major cause of habitat loss on federal lands, and timber harvest on nonfederal lands. Lastly, we assessed the relative contributions a suite of terrestrial and marine factors to murrelet spatial distribution and trend at sea by examining spatial and temporal correlations, and using boosted regression tree (multivariate) analyses. The results of both these analyses suggest that conservation of suitable nesting habitat is key to murrelet conservation, but marine factors, especially factors that contribute to murrelet prey abundance, may play a role in murrelet distribution and trend.
Keywords
Brachyramphus marmoratus,
habitat suitability model,
marbled murrelet,
Northwest Forest Plan,
population monitoring,
population trends,
nesting habitat trends,
effectiveness monitoring,
seabird,
old-growth forest.
Citation
Falxa, Gary A.; Raphael, Martin G., tech. coords. 2016. Northwest Forest Plan—the first 20 years (1994–2013): status and trend of marbled murrelet populations and nesting habitat. Gen. Tech. Rep. PNW-GTR-933. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 132 p.
