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 variation in their ventral plumage, ranging from reddish to whitish and from heavily spotted to no spots at all. In heterogeneous landscapes in Switzerland and Israel, reddish barn owls (Tyto alba) inhabit territories with proportionally more arable fields and consume proportionally more voles than their whiter counterparts. This is consistent with the habitat-matching choice hypothesis, but whether this also occurs in other regions and with the American barn owl has not yet been tested. This study sought to examine the relationships among prey composition, landscape composition, and degree of reddishness in barn owls throughout Napa Valley, CA. Pellet analysis was used to determine the proportion of mice (Peromyscus, Reithrodontomys, and Mus), voles (Microtus), and gophers (Thomomys) in the owls’ diet. The results show clear evidence for the existence of polymorphism in the heterogeneous landscapes within and surrounding vineyards, though the role of habitat heterogeneity remains incompletely resolved. These data also further reveal insights into predator-prey relationships and potentially provide vineyard producers with information about pest removal services.