Modeling Avian Habitat Suitability in Puget Sound

Our study provides valuable information about the environmental drivers of bird distribution and abundance and identifies important areas for birds in Puget Sound. The key findings from our study are:

• Estuarine emergent wetlands, mudflats, and freshwater emergent wetlands are important explanatory variables for modeling the occurrence and abundance of our five study species. Puget Sound estuary restoration and management projects that restore or protect these features can benefit a variety of estuary birds, including waterfowl, shorebirds, and landbirds.

• Prospective restoration sites that lie within historical wetlands, have currently low avian abundance, and have space for marsh migration have a high potential to benefit estuary birds.

• Standardizing monitoring efforts across seasons and basins in Puget Sound estuaries will improve our understanding of avian-habitat relationships and increase the effectiveness of habitat management interventions.

The coastal ecosystems of Puget Sound have been severely altered since European settlement. Less than 25% of the region’s historical estuarine wetlands remain, and shorelines have become shorter, straighter, and significantly more developed (Fresh et al. 2011). As a result, there is less coastal and estuarine habitat available to terrestrial and aquatic wildlife, and much of what remains is fragmented or otherwise degraded. Much attention has been paid to the impacts of coastal and wetland habitat loss and degradation on salmon populations and fisheries, but many other wildlife species, including birds, are affected as well.

Meaningful recovery of estuary bird communities in Puget Sound requires that we have a clear understanding of species status and trends, where and when they occur, and the environmental conditions and human pressures that influence their occurrence. 

Habitat suitability models use species distribution data and environmental attributes to identify the most influential variables explaining species occurrence (e.g., presence/absence) and abundance (e.g., how many in a given area). These models can be used to identify potential suitable habitat areas for birds, and can identify key environmental features associated with birds to include in restoration projects. They can also be used to assess how the loss of key environmental features might negatively impact birds, such as under future climate change conditions.  

We defined the study area as the Puget Sound and southern Salish Sea region of Washington State. The study area is restricted to the marine waters of Washington State east of Cape Flattery, and includes the U.S. portions of the Strait of Juan de Fuca, the southern Strait of Georgia, Hood Canal, Puget Sound proper and several other smaller basins. The study area contains portions of the ancestral lands of tribes signatory to the Treaty of Point Elliot, Medicine Creek, and Point No Point. The study area boundary was derived from the Submerged Vegetation Monitoring Program (Christiaen et al. 2019) and expanded to include Lake Washington and the city of Seattle. 

Port Susan Bay

We defined a second case study area spanning Port Susan Bay and southern Skagit Bay for estuarine wetland restoration scenario modeling. We selected this region as a case study because of ongoing progress in large-scale restoration across the Stillaguamish River delta.

We modeled habitat suitability for the five estuarine marsh bird narrative species across the Puget Sound during the seasons in which they occur in the region. These models relate bird occurrence and abundance from survey and community science data ( eBird ) with remotely-sensed land cover, tidal, and aquaculture data. The models provide two valuable pieces of information to inform conservation and restoration decisions: identification of the drivers of bird distributions, and maps showing when and where the species occur in the Puget Sound.

We found that availability of estuarine emergent wetland, mudflat, and palustrine wetland (all types) best predicted marsh bird occurrence. Where the species occurred, their relative abundance was most strongly predicted by cover of agriculture, estuarine emergent wetland, and mudflat as well as survey effort. The maps in the Imagery Viewer below show the predicted relative abundance (or occurrence probability) of marsh birds across the Puget Sound for each season, and can be used to help identify priority areas for conservation.

We conducted a restoration scenario modeling exercise to evaluate the potential benefit of estuarine wetland restoration in the Puget Sound. We used our bird-habitat suitability models to predict how many marsh birds might occur if all estuarine wetlands were restored to their original extent. We conducted this scenario modeling exercise at two spatial extents - across the entire Puget Sound, and within a case study area spanning Port Susan Bay and southern Skagit Bay - for two species in one season each.

We found that Greater Yellowlegs winter abundance was expected to increase by 20.7% if wetlands were restored to their original extent across the entire Puget Sound study area.

Within the Port Susan Bay study area, Greater Yellowlegs winter abundance was expected to increase by 1.7%.

For Northern Pintail, we found that spring abundance was expected to increase by 335% if wetlands were restored to their original extent across the entire Puget Sound study area.

Within the Port Susan Bay study area, Northern Pintail spring abundance was expected to increase by 204%.

Michel, N., T. Bayard, A. Summers, G. Slater, and K. Spragens. 2021. Avian Habitat Suitability Models for Puget Sound Estuary Birds. Prepared for the Puget Sound Ecosystem Monitoring Program, Puget Sound Partnership. Tacoma, WA, USA.

• Full Report:  https://pspwa.box.com/v/AvianHabModel 

• Summary Materials:  https://pspwa.box.com/v/AvHabModSummary 

• Species Profiles:  https://pspwa.box.com/v/AvianHabModA 

This study was supported by the Stillaguamish Tribe of Indians with funding from the Puget Sound Partnership (#2020-49) and benefitted from the input of our technical advisory group members: Tish Conway-Cranos (WDFW), Kit Crump (Snohomish County), Melanie Davis (USGS), Jason Griffith (Stillaguamish Tribe), Greg Hood (Skagit Watershed Cooperative), and members of the Puget Sound Ecosystem Monitoring Program Marine Birds Work Group. We also acknowledge the data owners whose contributions made this work possible, including Ecostudies Institute, Jamestown S’Klallam Tribe, Olympic Peninsula Audubon Society, Samish Indian Nation, Skokomish Tribe, Stillaguamish Tribe, U.S. Geological Survey, Washington Department of Fish & Wildlife, and all the community scientists who submitted their observations to eBird.