Notes on the Introduced Small Mammals of Tinian, Mariana Islands

Abstract: The negative effects of introduced small mammals have been well documented on islands, but their presence in the Mariana Islands warrants special attention, as they are an important prey species of the introduced brown treesnake (Boiga irregularis), which devastated the avifauna of Guam and remains a threat for introduction to nearby islands. The U.S. Navy has a major presence in the Mariana Islands and is charged with maintaining biosecurity protocols when transporting equipment between islands. We conducted small mammal trapping on Tinian, located approximately 165 km northeast of Guam, in 2017 as a baseline survey of introduced species distribution in areas used for military training. These data will facilitate long-term monitoring of introduced small mammals and early detection of newly established species. We also report an updated Catch Per Unit Effort index of small mammal abundance and tested for differences in capture success across species and between two trap types: Sherman live traps and Victor snap traps. We confirmed general patterns of abundance and distribution from previous sampling on Tinian: Rattus diardii and Suncus murinus were common and widespread, Mus musculus less common and more patchy in distribution, R. norvegicus rare, and R. exulans not detected. Comparisons between Sherman and Victor traps showed important differences in species-specific capture rates on Tinian and aligned with previous research from the Mariana Islands.