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. Keywords: abundance, biosecurity, distribution, index, introduced small mammals, Tinian, trap comparison
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.
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.
Islands can be powerful demonstrations of how destructive invasive species can be on endemic faunas and insular ecologies. Oceanic islands in the eastern Indian Ocean have suffered dramatically from ...the impact of one of the world’s most destructive invasive species, the black rat, causing the loss of endemic terrestrial mammals and ongoing threats to ground-nesting birds. We use molecular genetic methods on both ancient and modern samples to establish the origins and minimum invasion frequencies of black rats on Christmas Island and the Cocos-Keeling Islands. We find that each island group had multiple incursions of black rats from diverse geographic and phylogenetic sources. Furthermore, contemporary black rat populations on these islands are highly admixed to the point of potentially obscuring their geographic sources. These hybridisation events between black rat taxa also pose potential dangers to human populations on the islands from novel disease risks. Threats of ongoing introductions from yet additional geographic sources is highlighted by genetic identifications of black rats found on ships, which provides insight into how recent ship-borne human smuggling activity to Christmas Island can negatively impact its endemic species.
We compared track-tube sampling with mark–recapture livetrapping and evaluated a track-tube index, defined as the number of track tubes with identifiable small mammal tracks during a 4-night period, ...as a predictor of small mammal abundance estimates in North Dakota grasslands. Meadow voles (Microtus pennsylvanicus) were the most commonly recorded species by both methods, but were underrepresented in track-tube sampling, whereas 13-lined ground squirrels (Spermophilus tridecemlineatus) and Franklin's ground squirrels (S. franklinii) were overrepresented in track-tube sampling. Estimates of average species richness were lower from track tubes than from livetrapping. Regression models revealed that the track-tube index was at best a moderately good predictor of small mammal population estimates because both the form (linear versus curvilinear) and slope of the relationship varied between years. In addition, 95% prediction intervals indicated low precision when predicting population estimates from new track-tube index observations. Track tubes required less time and expense than mark–recapture and eliminated handling of small mammals. Using track tubes along with mark–recapture in a double sampling for regression framework would have potential value when attempting to estimate abundance of small mammals over large areas.
Although it is generally accepted that introduced small mammals have detrimental effects on island ecology, our understanding of these effects is frequently limited by incomplete knowledge of small ...mammal distribution, density, and biomass. Such information is especially critical in the Mariana Islands, where small mammal density is inversely related to effectiveness of Brown Tree Snake (Boiga irregularis) control tools, such as mouse-attractant traps. We used mark-recapture sampling to determine introduced small mammal distribution, density, and biomass in the major habitats of Guam, Rota, Saipan, and Tinian, including grassland, Leucaena forest, and native limestone forest. Of the five species captured, Rattus diardii (sensu Robins et al. 2007) was most common across habitats and islands. In contrast, Mus musculus was rarely captured at forested sites, Suncus murinus was not captured on Rota, and R. exulans and R. norvegicus captures were uncommon. Modeling indicated that neophobia, island, sex, reproductive status, and rain amount influenced R. diardii capture probability, whereas time, island, and capture heterogeneity influenced S. murinus and M. musculus capture probability. Density and biomass were much greater on Rota, Saipan, and Tinian than on Guam, most likely a result of Brown Tree Snake predation pressure on the latter island. Rattus diardii and M. musculus density and biomass were greatest in grassland, whereas S. murinus density and biomass were greatest in Leucaena forest. The high densities documented during this research suggest that introduced small mammals (especially R. diardii) are impacting abundance and diversity of the native fauna and flora of the Mariana Islands. Further, Brown Tree Snake control and management tools that rely on mouse attractants will be less effective on Rota, Saipan, and Tinian than on Guam. If the Brown Tree Snake becomes established on these islands, high-density introduced small mammal populations will likely facilitate and support a high-density Brown Tree Snake population, even as native species are reduced or extirpated.
Conservation and management of small mammals requires reliable knowledge of population size. We investigated precision of mark–recapture and removal abundance estimates generated from live-trapping ...and snap-trapping data collected at sites on Guam (n = 7), Rota (n = 4), Saipan (n = 5), and Tinian (n = 3), in the Mariana Islands. We also evaluated a common index, captures per unit effort (CPUE), as a predictor of abundance. In addition, we evaluated cost and time associated with implementing live-trapping and snap-trapping and compared species-specific capture rates of selected live- and snap-traps. For all species, mark–recapture estimates were consistently more precise than removal estimates based on coefficients of variation and 95% confidence intervals. The predictive utility of CPUE was poor but improved with increasing sampling duration. Nonetheless, modeling of sampling data revealed that underlying assumptions critical to application of an index of abundance, such as constant capture probability across space, time, and individuals, were not met. Although snap-trapping was cheaper and faster than live-trapping, the time difference was negligible when site preparation time was considered. Rattus diardii spp. captures were greatest in Haguruma live-traps (Standard Trading Co., Honolulu, HI) and Victor snap-traps (Woodstream Corporation, Lititz, PA), whereas Suncus murinus and Mus musculus captures were greatest in Sherman live-traps (H. B. Sherman Traps, Inc., Tallahassee, FL) and Museum Special snap-traps (Woodstream Corporation). Although snap-trapping and CPUE may have utility after validation against more rigorous methods, validation should occur across the full range of study conditions. Resources required for this level of validation would likely be better allocated towards implementing rigorous and robust methods.
Estimating the detection probability of introduced organisms during the pre-monitoring phase of an eradication effort can be extremely helpful in informing eradication and post-eradication monitoring ...efforts, but this step is rarely taken. We used data collected during 11 nights of mark-recapture sampling on Aguiguan, Mariana Islands, to estimate introduced kiore (Rattus exulans Peale) density and detection probability, and evaluated factors affecting detectability to help inform possible eradication efforts. Modelling of 62 captures of 48 individuals resulted in a model-averaged density estimate of 55 kiore/ha. Kiore detection probability was best explained by a model allowing neophobia to diminish linearly (i.e. capture probability increased linearly) until occasion 7, with additive effects of sex and cumulative rainfall over the prior 48 hours. Detection probability increased with increasing rainfall and females were up to three times more likely than males to be trapped. In this paper, we illustrate the type of information that can be obtained by modelling mark-recapture data collected during pre-eradication monitoring and discuss the potential of using these data to inform eradication and post-eradication monitoring efforts.
Although it is generally accepted that introduced small mammals have detrimental effects on island ecology, our understanding of these effects is frequently limited by incomplete knowledge of small ...mammal distribution, density, and biomass. Such information is especially critical in the Mariana Islands, where small mammal density is inversely related to effectiveness of Brown Tree Snake (Boiga irregularis) control tools, such as mouse-attractant traps. We used mark-recapture sampling to determine introduced small mammal distribution, density, and biomass in the major habitats of Guam, Rota, Saipan, and Tinian, including grassland, Leucaena forest, and native limestone forest. Of the five species captured, Rattus diardii (sensu Robins et al. 2007) was most common across habitats and islands. In contrast, Mus musculus was rarely captured at forested sites, Suncus murinus was not captured on Rota, and R. exulans and R. norvegicus captures were uncommon. Modeling indicated that neophobia, island, sex, reproductive status, and rain amount influenced R. diardii capture probability, whereas time, island, and capture heterogeneity influenced S. murinus and M. musculus capture probability. Density and biomass were much greater on Rota, Saipan, and Tinian than on Guam, most likely a result of Brown Tree Snake predation pressure on the latter island. Rattus diardii and M. musculus density and biomass were greatest in grassland, whereas S. murinus density and biomass were greatest in Leucaena forest. The high densities documented during this research suggest that introduced small mammals (especially R. diardii) are impacting abundance and diversity of the native fauna and flora of the Mariana Islands. Further, Brown Tree Snake control and management tools that rely on mouse attractants will be less effective on Rota, Saipan, and Tinian than on Guam. If the Brown Tree Snake becomes established on these islands, high-density introduced small mammal populations will likely facilitate and support a high-density Brown Tree Snake population, even as native species are reduced or extirpated.
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