[Truncated abstract] The dibbler, Parantechinus apicalis, is an endangered marsupial that exists on Boullanger, Whitlock and Escape islands off Jurien Bay in Western Australia. The introduced house mouse, Mus domesticus, exists on Boullanger and Whitlock islands, and the King’s skink, Egernia kingii, inhabits Boullanger and Escape islands. The grey-bellied dunnart, Sminthopsis griseoventer, exists on Boullanger Island. Over the last 150 years, the wedge-tailed shearwater, Puffinus pacificus, has colonised the islands to varying degrees. The interaction between dibblers and other island species is not clear. The purpose of this study was to determine the main factors regulating the dynamics of mammals, and in particular dibblers, on the Jurien islands. This was achieved by examining the effect of seabirds, the competitive interactions between species living on the islands, and seasonal changes in the environment. Animals were trapped for a period of 30 months, and their population structure, body condition, longevity, habitat preferences, diet and ecophysiology were examined. The results presented support the theory that by increasing soil nutrient concentrations, burrowing seabirds increase the primary productivity of islands, which has flow on effects to other trophic levels. Densities of seabirds and soil nutrient concentrations were highest on Whitlock Island, intermediate on Escape Island, and lowest on Boullanger Island . . .Thirty-five percent of dibblers on Escape Island were missing their tail or a limb, probably as a result of aggression from King’s skinks. Competition from high numbers of house mice on Boullanger Island, and from high numbers of King’s skinks on Escape Island, may increase the occurrence of male die-off on these islands. The better body condition and greater longevity of dibblers on Whitlock Island, despite high numbers of house mice, suggests that abundant resources are available to sustain both species. This study demonstrates that high densities of seabirds positively affect the population dynamics of mammals on the Jurien islands. Burrowing seabirds appear to influence the dynamics of dibblers more so than competition from house mice or King’s skinks. The findings from this study will assist the Dibbler Recovery Team with future management decisions regarding the viability of dibblers on the Jurien islands, and with decisions regarding the necessity to control house mouse numbers in the presence of native species.