Portland State University. Department of Biology
Michael T. Murphy
Date of Award
Doctor of Philosophy (Ph.D.) in Biology
1 online resource (vi, 166 pages)
Over fifty percent of humans live in cities. The environmental cost of this is massive, as is the potential for utilizing privately held yards as an integral part of conservation in urban areas. The Backyard Habitat Certification Program (BHCP) in Portland, Oregon, was established to reduce invasive plants, support wildlife, and promote conservation. The program involves > 3000 yards certified at three tiers. While onsite inspections are required to verify compliance, there has never been an assessment of the value of these yards to wildlife. In chapter 1 I examined the relationships between the urban landscape and bird distributions outside of yards. In chapter 2 I evaluated the ability of the program to separate yards by assessing differences in vegetation structure and composition. In chapter 3 I tested if avian abundance, richness and diversity in yards are a product of responses to yard or landscape vegetation structure. I collected avian data at 146 yards and 73 random locations in 2013 and 2014. I used public landscape data and collected yard data in the field. Avian abundance, richness, and diversity were affected negatively by urbanization (especially impervious surface) and population density, but positively by tree cover. The BHCP was effective at distinguishing platinum yards from others, but overlap was relatively high among gold, silver and uncertified yards. Avian abundance, richness and diversity within yards was less affected by yard vegetation than the structure of habitat in the surrounding landscape. Species responded individualistically to yard vegetation and the urban landscape, and response was a continuum of tolerance to urbanization. Ultimately, the ability of yards to support wildlife will depend on wide scale neighborhood participation.
Gibbs, Andrew Daniel, "Understanding the Impacts of Urbanization on the Avian Community of Portland Oregon and Evaluation of the Portland Oregon Backyard Habitat Certification Program" (2018). Dissertations and Theses. Paper 4386.