Oxbow Farm & Conservation Center

Common yellowthroat in field-edge grasses. Photo courtesy of Dr. John Marzluff

In 2016, CREOi provided Oxbow Farm & Conservation Center with a grant to study bird diversity and habitat use on the 240 acres of agricultural and forest land managed by Oxbow.  Data were collected from point counts, spot mapping and mist netting to provide information on bird species found in upland forest areas, lowland semi-natural forests, lowland areas where ecological restoration has been started, and unrestored lowland areas (Figure 1).  Between April and August of 2016, researchers observed 78 species across the Oxbow property.  Nesting success of common species was approximately 50%, suggesting that nest predation and parasitism are not unusually high in this environment despite the high proportion of edge habitat.

Figure 1: Map of point counts, showing species richness and focal habitat types

Avian diversity was lowest in farm fields, but several birds with declining regional populations, including Savannah sparrows, use or nest in field-edge grasses. Based on these findings, Oxbow is setting a new mowing schedule that will avoid mowing tall grass areas during the summer nesting season, thereby improving the habitat value and perhaps increasing the pest reduction benefits to the farm.

Restored and unrestored riparian buffer areas and semi-natural areas in the lowland portions of the property together create a complex patchwork of shrubs, grass, saplings, and trees and contain the highest levels of bird diversity. Levels of species richness among these three land use types were statistically indistinguishable from one another (p>0.05), although unrestored areas trended highest in bird diversity. This finding, though initially surprising, reflects the young age of most restoration plantings on the property and the presence of remnant native vegetation in many of the as yet unrestored areas. Overall, restoration areas and unrestored areas have similar

Figure 2: NMDS ordination (where distance in graph represents dissimilarity in species composition), showing progression (arrow) of bird communities from low vegetation habitats (left) to tall vegetation (right).

avian species assemblages (Figure 2). The oldest restoration areas, which have developed more vegetation height and structure, have avian assemblages more similar to upland forest areas. The lowland riparian areas are used by several regionally declining species such as American goldfinch, black-capped chickadee, white-crowned sparrow, rufous hummingbird, Swainson’s thrush, and willow flycatcher.

Although species richness in upland habitats was found to be somewhat lower than lowland habitats, the suite of birds in the upland forests included several birds of particular conservation interest (Swainson’s thrush, Wilson’s warbler, and Pacific wren). Because these species are declining regionally and much of their global population is centered in the Pacific Northwest, protecting upland habitat for them and improving habitat in suitable lowland semi-natural areas will continue to be a priority for Oxbow.

Land managers at Oxbow will use the information from this study in concert with data on regional trends for bird species (Partners in Flight Science Committee 2013) to guide continued restoration efforts in each habitat type. Oxbow will also share findings with local landowners and other stakeholders. Ongoing monitoring in partnership with the Puget Sound Bird Observatory will continue to add to this dataset and build an understanding of temporal trends as restoration work continues.

Avian biologist Lauren Walker demonstrating banding to summer campers

This project served as the basis for developing new environmental educational programming at Oxbow as well. Education staff integrated bird research and concepts in ecology into 2016 summer camp activities, and the staff are now teaching an in-school module, “Calling all Birds”, to creatively introduce complex ecological concepts (e.g., habitat, adaptation, and ecological niche) to young children. In the 2017-18 school year, Oxbow will be partnering with a low-income elementary school in Monroe, WA to deliver quality environmental education via monthly educational experiences for the Kindergarten classes.  “Calling All Birds” will be one of the lessons delivered to the Kindergarten classes. ($15,000)

Table 1: Habitat resources, associated bird species, and management implications