Effectiveness of Snap and A24-Automated Traps and Broadcast Anticoagulant Bait in Suppressing Commensal Rodents in Hawaii

Commensal rodents (invasive rats, Rattus spp.; house mice, Mus musculus) are well established globally. They threaten human health by disease transfer and impact economies by causing agricultural damage. On island landscapes, they are frequent predators of native species and affect biodiversity. To provide managers with better information regarding methods to suppress commensal rodent populations in remote island forests, in 2016 we evaluated the effectiveness of continuous rat trapping using snap-traps, Goodnature®A24 self-resetting rat traps, and a 1-time (2-application) hand-broadcast of anticoagulant rodenticide bait pellets (Diphacinone-50) applied at 13.8 kg/ha per application in a 5-ha forest on Oahu, Hawaii, USA. We compared rat and mouse abundance at the rat trapping site to a reference site by monitoring rodent tracking tunnels, which are baited ink cards in tunnels that allow footprints of animal visitors to be identified. We found that trapping reduced rat, but not mouse, abundance. The rodenticide treatment did not further reduce rat populations (P = 0.139), but temporarily reduced the mouse populations (P \u3c 0.001; from 33% tracking to 0% for 1.3 months). Our study highlighted the role of continuous trapping for rats and rodenticide baiting for mice as effective methods to suppress commensal rodent populations in remote island forests to protect native species biodiversity

Hawai‘i Forest Review: Synthesizing the Ecology, Evolution, and Conservation of a Model System

As the most remote archipelago in the world, the Hawaiian Islands are home to a highly endemic and disharmonic biota that has fascinated biologists for centuries. Forests are the dominant terrestrial biome in Hawai‘i, spanning complex, heterogeneous climates across substrates that vary tremendously in age, soil structure, and nutrient availability. Species richness is low in Hawaiian forests compared to other tropical forests, as a consequence of dispersal limitation from continents and adaptive radiations in only some lineages, and forests are dominated by the widespread Metrosideros species complex. Low species richness provides a relatively tractable model system for studies of community assembly, local adaptation, and species interactions. Moreover, Hawaiian forests provide insights into predicted patterns of evolution on islands, revealing that while some evidence supports “island syndromes,” there are exceptions to them all. For example, Hawaiian plants are not as a whole less defended against herbivores, less dispersible, more conservative in resource use, or more slow-growing than their continental relatives. Clearly, more work is needed to understand the drivers, sources, and constraints on phenotypic variation among Hawaiian species, including both widespread and rare species, and to understand the role of this variation for ecological and evolutionary processes, which will further contribute to conservation of this unique biota. Today, Hawaiian forests are among the most threatened globally. Resource management failures – the proliferation of non-native species in particular – have led to devastating declines in native taxa and resulted in dominance by novel species assemblages. Conservation and restoration of Hawaiian forests now rely on managing threats including climate change, ongoing species introductions, novel pathogens, lost mutualists, and altered ecosystem dynamics through the use of diverse tools and strategies grounded in basic ecological, evolutionary, and biocultural principles. The future of Hawaiian forests thus depends on the synthesis of ecological and evolutionary research, which will continue to inform future conservation and restoration practices

Data from: Microhabitat heterogeneity and a non-native avian frugivore drive the population dynamics of an island endemic shrub, Cyrtandra dentata

Understanding of the role of environmental change in the decline of endangered species is critical to designing scale-appropriate restoration plans. For locally endemic rare plants on the brink of extinction, frugivory can drastically reduce local recruitment by dispersing seeds away from geographically isolated populations. Dispersal of seeds away from isolated populations can ultimately lead to population decline. For localized endemic plants, fine-scale changes in microhabitat can further limit population persistence. Evaluating the individual and combined impact of frugivores and microhabitat heterogeneity on the short-term (i.e. transient) and long-term (i.e. asymptotic) dynamics of plants will provide insight into the drivers of species rarity. In this study, we used four years of demographic data to develop matrix projection models for a long-lived shrub, Cyrtandra dentata (H. St. John & Storey) (Gesneriaceae), which is endemic to the island of O'ahu in Hawai'i. Furthermore, we evaluated the individual and combined influence of a non-native frugivorous bird, Leiothrix lutea, and microhabitat heterogeneity on the short-term and long-term C. dentata population dynamics. Frugivory by L. lutea decreased the short-term and long-term population growth rates. However, under the current level of frugivory at the field site the C. dentata population was projected to persist over time. Conversely, the removal of optimum microhabitat for seedling establishment (i.e. rocky gulch walls and boulders in the gulch bottom) reduced the short-term and long-term population growth rates from growing to declining. Survival of mature C. dentata plants had the greatest influence on long-term population dynamics, followed by the growth of seedlings and immature plants. The importance of mature plant survival was even greater when we simulated the combined effect of frugivory and the loss of optimal microhabitat, relative to population dynamics based on field conditions. In the short-term (10 years), however, earlier life stages had the greatest influence on population growth rate. Synthesis and applications. This study emphasizes how important it is to decouple rare plant management strategies in the short versus long-term in order to prioritize restoration actions, particularly when faced with multiple stressors not all of which can be feasibly managed. From an applied conservation perspective, our findings also illustrate that the life stage that, if improved by management, would have the greatest influence on population dynamics is dependent on the timeframe of interest and initial conditions of the population

Cyrtandra_dentata_matrices_2010_2014

This file contains mean transition matrices from 2010–2011, 2011–2012, 2012–2013, and 2013–2014 from a geographically isolated population of a long lived shrub, Cyrtandra dentata, from the Kahanahāiki Management Unit (36 ha), located in the northern Wai‘anae Mountain Range, on the island of O‘ahu (21° 32’ N, -158°12’ W

Large-scale Aerial Baiting to Suppress Invasive Rats in Hawaii: Efficacy of Diphacinone and Associated Risks

Invasive rats are among the most damaging animals to native species on many island ecosystems including those in Hawaii. On Oahu Island, U.S. Army Garrison Natural Resources Program currently manages invasive rat populations to protect natural resources by using grids of A24 automated traps, and previously snap-trap grids and rodenticide bait stations. Despite these control efforts generally suppressing rats, some lands with natural resources that are at risk to rat predation are not easily accessible for implementing these traditional rat control methods. In a 430-ha mesic forest on Oahu where ungulates are excluded and site access is limited due to military training and presence of live ordnance, we tested the efficacy of aerial application of anticoagulant rodenticide bait pellets (Diphacinone-50 Conservation), applied in two applications at a rate of 12.82 kg/ha per application. We measured the effectiveness of the rodenticide bait application by deploying tracking tunnels (inked and baited cards to identify rat presence) before, during, and after applications within treated and nearby untreated areas. Due to restricted access, we failed to estimate nest success of an endangered bird; yet previous research showed rat control increases this bird’s population. We also measured diphacinone residues in stream water at the treatment site to determine this method’s risk level to the aquatic ecosystem. The aerial application resulted in immediate and sustained reduction in the rat population, as evidenced by rat activity decreasing from ~44% to 3.8% during the first three months after bait application and maintained <20% rat activity for 10 months. Trail cameras and recovered rat carcasses also highlighted effectiveness. One of 34 stream samples analyzed had detectable diphacinone residues and this single sample was taken one week after application and it had very low levels of diphacinone (below levels quantifiable). Aerial application of diphacinone appears to be an efficient and effective rat suppression technique for natural resource protection in complex landscapes

Effectiveness of Snap-trapping, Goodnature A24 Automated Traps, and Hand-broadcast of Diphacinone Anticoagulant Baits to Suppress Invasive Rats (Rattus spp.) and Mice (Mus musculus) in Hawaiian Forest

Invasive rodents (rats and mice) commonly occur on islands and often damage natural resources largely by predation of native species. Suppressing invasive rodent populations and their damages is therefore a common practice in many parts of the Hawaiian Islands, and land managers such as the Army Natural Resources Program on Oahu often control rodent populations by using large-scale rat snap-trapping and Goodnature A24 automated rat traps (henceforth A24s). While rat traps can be effective at suppressing rat populations, mouse populations are not generally suppressed and may expand greatly. In an effort to reduce rodent populations to levels below that accomplished with rat traps alone at a 5-ha mesic forest on Oahu (Ohikilolo), we assessed the effectiveness of a one-time (two application) hand-broadcast of anticoagulant (Diphacinone-50) bait pellets applied at 13.8 kg/ha per application while A24s and rat snap-traps were active. We monitored rat and mouse activity during trapping and before, during, and after the bait applications using tracking tunnels, which are baited ink cards placed in tunnels so that foot prints of animal visitors can be identified. We found that rat trapping alone was effective at reducing rat populations but not the mouse population, and that the one-time hand-broadcast of diphacinone bait reduced both rat and mouse activity to 0% tracking for about 1 month. However, rat and mouse populations rebounded 2 months later to 15% rat tracking and 41% mouse tracking, which were roughly pre-treatment levels. Rat suppression using A24s at Ohikilolo appeared much more effective year-round than at a nearby 26 ha site (Kahanahaiki), though mouse suppression was poor at Ohikilolo relative to Kahanahaiki. The hand-broadcast of diphacinone bait at both Ohikilolo and Kahanahaiki was effective but short-lived, so repeated baiting during the seasonal peaks in rodent abundance and increasing the size of the buffer area would more likely protect target natural resources from rats and mice

Large-scale Aerial Baiting to Suppress Invasive Rats in Hawaii: Efficacy of Diphacinone and Associated Risks

Invasive rats are among the most damaging animals to native species on many island ecosystems including those in Hawaii. On Oahu Island, U.S. Army Garrison Natural Resources Program currently manages invasive rat populations to protect natural resources by using grids of A24 automated traps, and previously snap-trap grids and rodenticide bait stations. Despite these control efforts generally suppressing rats, some lands with natural resources that are at risk to rat predation are not easily accessible for implementing these traditional rat control methods. In a 430-ha mesic forest on Oahu where ungulates are excluded and site access is limited due to military training and presence of live ordnance, we tested the efficacy of aerial application of anticoagulant rodenticide bait pellets (Diphacinone-50 Conservation), applied in two applications at a rate of 12.82 kg/ha per application. We measured the effectiveness of the rodenticide bait application by deploying tracking tunnels (inked and baited cards to identify rat presence) before, during, and after applications within treated and nearby untreated areas. Due to restricted access, we failed to estimate nest success of an endangered bird; yet previous research showed rat control increases this bird’s population. We also measured diphacinone residues in stream water at the treatment site to determine this method’s risk level to the aquatic ecosystem. The aerial application resulted in immediate and sustained reduction in the rat population, as evidenced by rat activity decreasing from ~44% to 3.8% during the first three months after bait application and maintained <20% rat activity for 10 months. Trail cameras and recovered rat carcasses also highlighted effectiveness. One of 34 stream samples analyzed had detectable diphacinone residues and this single sample was taken one week after application and it had very low levels of diphacinone (below levels quantifiable). Aerial application of diphacinone appears to be an efficient and effective rat suppression technique for natural resource protection in complex landscapes

Rat Control for the Protection of Endangered Birds, Plants, and Tree Snails on the Island of Oahu, Hawaii

Since 1997, the Oahu Army Natural Resource Program has been controlling rats using diphacinone rodenticide in small-scale bait station grids in combination with rat traps for the protection of one endangered forest bird species, 5 species of endangered Oahu tree snails, and 9 species of endangered plants in 2 mountain ranges on the island of Oahu. Endangered tree snail and some plant populations are protected year-round. Other plants are only protected during their flowering/fruiting season, with small-scale baiting grids in combination with rat traps; and the Oahu Elepaio is only protected during its breeding season, with small-scale bait station grids in combination with rat traps centered on territories. In May 2009, year-round rat control was initiated over a 26-ha forested management unit on Oahu with 440 snap traps. The New Zealand Department of Conservation current best practice rat kill-trapping technology is being utilized for the first time in Hawaii with this large-scale trapping effort. Rat activity within the management unit will be monitored through the use of tracking tunnels. Forest health (seed rain and seedling germination), endangered plant recruitment, endangered tree snail survival, and native invertebrate abundance will be monitored closely to determine the effectiveness of this large-scale trapping effort. The Oahu Army Natural Resource Program is working towards integrating multiple control methods (bait station grids, large-scale rat trap grids, predator-proof fencing, hand and targeted aerial application of rodenticide) over large-scale areas in an effort to determine the most effective means to control rats in Army-managed areas on Oahu

A Near Four-Decade Time Series Shows the Hawaiian Islands Have Been Browning Since the 1980s.

The Hawaiian Islands have been identified as a global biodiversity hotspot. We examine the Normalized Difference Vegetation Index (NDVI) using Climate Data Records products (0.05 × 0.05°) to identify significant differences in NDVI between neutral El Niño-Southern Oscillation years (1984, 2019) and significant long-term changes over the entire time series (1982-2019) for the Hawaiian Islands and six land cover classes. Overall, there has been a significant decline in NDVI (i.e., browning) across the Hawaiian Islands from 1982 to 2019 with the islands of Lānai and Hawaii experiencing the greatest decreases in NDVI (≥44%). All land cover classes significantly decreased in NDVI for most months, especially during the wet season month of March. Native vegetation cover across all islands also experienced significant declines in NDVI, with the leeward, southwestern side of the island of Hawaii experiencing the greatest declines. The long-term trends in the annual total precipitation and annual mean Palmer Drought Severity Index (PDSI) for 1982-2019 on the Hawaiian Islands show significant concurrent declines. Primarily positive correlations between the native ecosystem NDVI and precipitation imply that significant decreases in precipitation may exacerbate the decrease in NDVI of native ecosystems. NDVI-PDSI correlations were primarily negative on the windward side of the islands and positive on the leeward sides, suggesting a higher sensitivity to drought for leeward native ecosystems. Multi-decadal time series and spatially explicit data for native landscapes provide natural resource managers with long-term trends and monthly changes associated with vegetation health and stability