Invasive predators can negatively impact 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 over time during invasion. Additionally, 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. We present diets from 6 invasive populations in California, Oregon and Washington, and 1 native population in Minnesota and Wisconsin. Dietary diversity was greater in the invasive range across all taxonomic levels, with the leading edge of the invasion in California having the most diverse diet. Non-mammalian prey had higher importance in the invasive range, with amphibians and invertebrates represented most often.