Marbled murrelet (brachyramphus marmoratus) populations along the west coast of the United States have been in decline for over a century due primarily to widespread logging of coastal old-growth forests which provide large trees that are suitable for nesting and within reach of near-shore marine waters where they forage for fish. More recently, climate change is driving increased rates of forest disturbance (e.g. wildfire, bark beetle outbreaks) and also widespread changes in the marine food web that affect the foraging success of seabirds like the marbled murrelet. These stressors have resulted in marbled murrelets being listed as threatened by the US Fish and Wildlife Service and endangered by the Washington State Department of Fish and Wildlife.

This study advances our understanding of how climate, forest management, and forest succession interact to shape suitable nesting and foraging habitat for marbled murrelets. Understanding these relationships is critical to devising effective forest management strategies to sustain and recover populations of this federally threatened seabird. Mapping of areas with high nesting habitat suitability according to the model and quantifying the area of suitable habitat over time addresses the marbled murrelet habitat monitoring and trends reporting requirements of the Northwest Forest Plan. These reports provide valuable information for managers to understand the effectiveness of their recovery efforts and help adjust management plans to increase effectiveness in the future.

The US Forest Service and partner agencies perform regular surveys for marbled murrelets at-sea using boat transects along the US Pacific coast, and on land using transects, grid searches, and site visits. We identified and gathered data related to climate, near-shore foraging habitat, and forest structural attributes potentially related to the at-sea abundance or nest site selection of marbled murrelets. From these data, we trained models to predict at-sea abundance and the probability of occupied nest sites along coastal areas from Washington to California.

From the model projections, we quantified the area of suitable habitat within the NW Forest Plan management area and assessed trends in habitat and at-sea abundance over time across various subregions of Washington, Oregon, and California and also across different ownerships (e.g. federal, private). We identified hotspots of at-sea abundance and areas with high concentrations of nesting habitat that could be targeted for conservation actions to help sustain and recover this species.

We monitored murrelet populations offshore of the NWFP area from 2000
to 2013 to estimate population size and trend at several spatial scales. 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 trends. Results
indicate about 2.5 million acres 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 ands, and timber harvest on nonfederal lands.

Lastly, we assessed the relative contributions of 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.