Olea europaea (European olive) is invasive in Australia and widely planted in California. Vertebrates, particularly birds, mediate Olea seed dispersal. Fruits are large, but their sizes range widely. We measured fruit widths from 12 study stands in California and constructed esophageal probes in diameters spanning the resulting size range. We then obtained whole-bird frugivorous bird carcasses and used the probes to determine the fruit sizes that each bird species would be anatomically capable of swallowing. This allowed us to develop lists of potential dispersers for each study stand. Even stands with the largest measured fruits had several potential disperser species, but the list of species expanded greatly as fruit sizes decreased. Feral Olea stands with remarkably small fruits have been observed in California and Australia. An increase in the incidence of such stands might augment the regional spread rate for the species.