Graduation Date

Fall 2023

Document Type



Master of Science degree with a major in Natural Resources, option Wildlife

Committee Chair Name

Dr. Matthew Johnson

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Dr. Jeffrey Black

Third Committee Member Name

Dr. Barbara Clucas

Third Committee Member Affiliation

HSU Faculty or Staff

Subject Categories



Many raptor species exhibit plumage polymorphism. Through the expression of a particular phenotype, polymorphism allows individuals to exploit alternative spatial or temporal environments and food resources most successfully. Barn Owls display within-species variation in their plumage, ranging from reddish to whitish and from heavily spotted to having no spots at all. In heterogeneous landscapes in Europe and the Middle East, reddish Common Barn Owls (Tyto alba) inhabit territories with proportionally more arable fields and consume proportionally more voles than mice in contrast to their whiter counterparts; a phenomenon known as habitat matching choice. This study sought to quantify polymorphism in female and male American Barn Owls (Tyto furcata) in Napa Valley, CA and to examine the relationships among landscape composition around nests, prey composition, and degree of reddishness in this population. Adult owls were photographed, and plumage characteristics were analyzed using MATLAB software. Pellet analysis was used to determine the proportion of mice (Peromyscus, Reithrodontomys, and Mus), voles (Microtus), and gophers (Thomomys) in the owls’ diet. Analysis of these data with linear regressions showed evidence of plumage-based habitat and prey composition. Redder females selected less forested areas, but unlike the European and Middle Eastern owls, they provisioned fewer voles than whiter females. The results provide further evidence for the existence of polymorphism in heterogeneous landscapes, in this case within and surrounding vineyards. Additionally, the relationship between individual color and prey consumption provides ecologists insight into predator-prey relationships and potentially provides vineyard producers with information about pest removal services.

Citation Style

Journal of Wildlife Management


Thesis/Project Location


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