Invasive predators can have negative impacts on biological communities through top-down predation, but the ecological processes that shape the consumption of prey in novel communities are less understood. The “Enemy release hypotheses” and “Naïve prey hypothesis” are two explanations for why invasive species succeed in novel environments and, under these hypotheses, diets of invasive predators are expected to initially expand and then contract throughout the invasion process. Furthermore, differing invader densities, and fluctuations in climactic and biogeographic conditions that shape prey community composition are likely to influence prey availability and selection, but the relative importance of these factors has yet to be tested. Here we used DNA metabarcoding on intestinal samples to determine diet composition and diversity of Barred Owls (Strix varia) within their native and invasive ranges. Dietary diversity was greater in the invasive range across all taxonomic levels. Within the native range mice were the most consumed vertebrate (frequency of occurrence = 71%) but were a small component of invasive diet (26%). Non-mammalian prey items had higher importance within the invasive range. We provide preliminary evidence that expansion in hunting opportunities facilitates successful invasions.