A critical issue when managing for habitat in urban areas is habitat size. What is the minimum viable patch size for a species of concern? Can multiple smaller patches, such as yards and parks, collectively “scale up” to provide connected, suitable habitat? Michael Vermeulen, an M.S student at Portland State University, spoke at IUWC2019 about his work investigating avian species richness and diversity in small urban habitat patches, and how we can increase biodiversity in our yards.
Vermeulen notes that neighborhoods are highly fragmented habitats, consisting of patches of green space surrounded by an inhospitable matrix that includes residential areas, industrial areas, and roads. Habitat quantity can vary across the urban landscape, with some areas containing more vegetation, and different habitat patch sizes. Large parks (greater than 10 hectares) are known to support rich bird communities, while small parks are much less valuable to birds. However, collectively yards and small parks may have the ability to collectively provide suitable habitat for urban species. Vermeulen’s main questions are how bird richness and diversity varies between residential neighborhoods in Portland, OR, and whether the utilization of these small habitat patches by birds differs within these neighborhoods.
To address these questions, he selected sampling sites in two Portland neighborhoods, Hillsdale and Lents. Hillsdale is much more forested, while Lents was more residential. He selected all the parks in each region, and classified these as either “nature parks” if they had understory vegetation present, or “recreational parks.” Community-based scientists sampled birds at these parks, as well as residential stations scattered throughout the two neighborhoods. At residential sites, he also performed front yard vegetation surveys to assess the habitat structure they provide for birds.
Over the course of this study, he observed 39 bird species total. Of these, only 17 species accounted for 95% of all observations. These were all winter residents; no long distance migrants were sampled in abundance. Using non-metric multidimensional scaling, to compare the neighborhoods, Vermeulen found that there was a similar bird community composition between these two areas. On average, however, species richness and Shannon’s Diversity were both greater in the Hillsdale (more vegetated) neighborhood.
Comparisons were also made within sites. There was no difference in species richness between residential areas and nature parks in Hillsdale. In Lents, the less tree-canopied neighborhood, nature parks, and residential stations had similar species richness and diversity, but recreational parks had significantly lower values. Additionally, yard vegetation has an important role to play in bird habitat. Areas with more residential area understory canopy had significantly more diversity than those with less vegetation.
Vermeulen’s findings suggest that urban areas that might be lacking large, high-quality bird habitat (those parcels 10 hectares or larger,) do have the potential to “scale up” via individual management decisions and provide habitat of higher value. Increased vegetation and tree cover in neighborhoods, as well as the inclusion of understory shrubs in urban parks, can have a significantly positive impact on our urban bird communities.
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