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* Metric Name: Marbled Murrelet Suitable Nesting Habitat  

* Tier: 2  

* Data Vintage: 09/2017  

* Unit Of Measure: relative suitability ranging from **** 0 - 1.0  

* Metric Definition and Relevance: This data layer has been developed by an interagency team of scientists from the US Forest Service, US Fish and Wildlife Service, and Oregon State University. It was published in “Status and Trend of Nesting Habitat for the Marbled Murrelet Under the Northwest Forest Plan, 1993 to 2017” in 2021. It is part of the work to monitor the effectiveness of the Northwest Forest Plan. The data represent relative habitat suitability of habitat for marbled murrelet range in California for 2017; categorized as lower, moderate, and higher probability of nesting habitat, with probability gradients in each class.  

* Creation Method: Using Maxent species distribution models, the authors modeled the amount and distribution of probable nesting habitat in the murrelet’s range in 2017. Probability scores from Maxent provide information on the relative suitability of habitat. While thresholds were necessary in this report for estimating acres of habitat in different categories (e.g., comparing acres in 1993 to 2017), Maxent probability scores provide a complete, probabilistic map of habitat suitability.

Note: Imagery was obtained in late summer (July to September) rather than at
the change in the calendar year (December to January). Thus, some 2017 fires
were excluded from the analysis, such as the Chetco Bar Fire, which occurred
in late summer in 2017.

Within the higher probability nesting habitat, the authors estimated the
amount of contiguous habitat (core) versus the amount of habitat bounding core
habitat (edge) and habitat scattered in small forest fragments (scatter). The
authors considered this “core habitat” as the best habitat. Their models
indicate that there were 1.51 million acre of higher probability nesting
habitat over all lands in the murrelet’s range in Washington, Oregon, and
California 1 year prior to the start of the Northwest Forest Plan (NWFP) in
1993. Of this, 0.14 million acres were identified as core habitat, which are
defined as intact patches of higher probability nesting habitat >5.56 acre in
size. The authors estimated a net loss of about 1.4 percent in higher
probability nesting habitat across the NWFP area and 1.8 percent in core
habitat from 1993 to 2017. Their analysis estimates that in 2017 there were
3,175,539 acres of lower probability nesting habitat, 35,939 acres of moderate
probability nesting habitat, and 38,564 of higher probability habitat in
California.

The RRK team combined the Low (0.003 - 0.38), Moderate (0.381 - 0.645) and
High (0.646 - 1) suitability rasters into one raster. The modeled output
covers the entire range of Northern Spotted Owls: Washington, Oregon, and
northern California within the Northwest Forest Plan (NWFP) boundary. For RRK
purposes, it has been clipped to the Northern California region.

  

* Credits: Regional Ecosystem Office (REO) - Northwest Forest Plan https://www.fs.usda.gov/r6/reo/riec/ Lorenz, T.J.; Raphael, M.G.; Young, R.D.; Lynch, D.; Nelson, S.K.; McIver, W.R. 2021. Status and trend of nesting habitat for the marbled murrelet under the Northwest Forest Plan, 1993 to 2017. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 64 p.