Rodent Eradication Research Articles

Impacts of rodent eradication on seed predation and plant community biomass on a tropical atoll

AbstractInvasive rodent eradications are frequently undertaken to curb island biodiversity loss. However, the breadth of rodents’ ecological impact, even after eradication, is not always fully recognized. For example, the most widespread invasive rodent, the black rat (Rattus rattus), while omnivorous, eats predominantly seeds and fruit. Yet, the effects of seed predation release after eradication on plant communities and ecological functions are not well understood, posing a gap for island restoration. We examined the role of seed predation release following black rat eradication in changes to tree composition and aboveground biomass across an islet network (Palmyra Atoll) in the Central Pacific. We conducted repeated surveys of seed, juvenile, and adult tree biomass and survival in permanent vegetation plots before and after the eradication of rats. We observed a 95% reduction in seed predation for an introduced, previously cultivated tree population (Cocos nucifera). Juvenile tree biomass of all species increased 14‐fold, with C. nucifera increasing the most, suggesting that eradication increased this tree's competitive advantage. Indeed, based on stage‐structured demographic models, rat eradication led to a 10% increase in C. nucifera population growth rate. The effect of invasive rodent seed predation varies considerably among the plant species in a community and can shift competitive dynamics, sometimes in favor of invasive plants. These bottom‐up effects should be considered in evaluating the costs and benefits of eradication. Documenting the variation in invasive rodent diet items, along with long‐term surveys, can help prioritize island eradications where restoration is most likely to be successful.

Prevalence and factors associated with a higher or lower risk of exposure to Coxiella burnetii, Chlamydia abortus and Toxoplasma gondii in dairy cows that have aborted in Algeria.

In Algeria, the prevalence of causes of abortion on dairy cattle farms (whether infectious causes or not) has been little studied. The current study involved a serological analysis conducted between October 2014 and June 2016 in northern Algeria using an enzyme-linked immunosorbent assay test on blood samples taken from 368 cows that had aborted on 124 farms. It was complemented by a survey to identify the factors associated with a higher or lower risk of exposure to Coxiella burnetii, Chlamydia abortus and Toxoplasma gondii, using univariate logistic regression and then multivariate logistic regression. The individual serological prevalences obtained were 8.4% (31/368) for C. burnetii and 12.2% (45/368) for C. abortus. For T. gondii, the individual seroprevalence was 13.8% (51/368); the factors associated with a higher risk of individual exposure were the fourth month of gestation (odds ratio [OR] = 22.68; 95% confidence interval [CI]: 1.38-392.97) and the fifth month of gestation (OR = 25.51; 95% CI: 1.47-442.11). All the other factors identified by the multivariate logistic regression were associated with a lower risk of exposure. They are the inspection visits in 2015 (OR = 0.0006; 95% CI: 0.000004-0.12) and in 2016 (OR = 0.0005; 95% CI: 0.000002-0.13) and artificial insemination (OR = 0.15; 95% CI: 0.05-0.44) for C. burnetii ; winter (OR = 0.39; 95% CI: 0.15-1.00), spring (OR = 0.45; 95% CI: 0.20-0.97), and artificial insemination (OR = 0.27; 95% CI: 0.13-0.56) for C. abortus; and the number of gestations (OR = 0.38; 95% CI: 0.16-0.92) for T. gondii. The seroprevalence at herd level was 16.1% (20/124) for C. burnetii and 29.8% (37/124) for both C. abortus and T. gondii. At herd level, the risk factors associated with a higher risk of exposure to C. abortus and T. gondii were the practice of deworming (OR = 3.89; 95% CI: 1.53-9.89) and drilling individual wells as a source of drinking water (OR = 7.50; 95% CI: 2.11-26.69). For C. burnetii, the inspection visit in 2015 (OR = 0.02; 95% CI: 0.0008-0.65) and in 2016 (OR = 0.01; 95% CI: 0.0003-0.36), artificial insemination (OR = 0.21; 95% CI: 0.06-0.69) and rodent eradication (OR = 0.19; 95% CI: 0.06-0.57) were factors that reduced the risk of exposure.

Scenario analysis on the use of rodenticides and sex-biasing gene drives for the removal of invasive house mice on islands

Since the 1960s conservation efforts have focused on recovering island biodiversity by eradicating invasive rodents. These eradication campaigns have led to considerable conservation gains, particularly for nesting seabirds. However, eradications are complex and lengthy endeavors and are even more challenging when humans are co-inhabitants of the targeted island. Furthermore, the method of eradication matters and recent proposals to consider genetic technologies for rodent eradication require specific scrutiny. One such technology is the potential use of a gene drive for biasing offspring sex ratios in invasive house mice, Mus musculus, that would spread and prevent the production of one sex, allowing die-off from lack of reproduction and natural attrition. Practitioners can gain insight into the potential for adoption of this technology from examining stakeholder engagement. This paper uses scenario analysis to address the eradication of rodents on inhabited and uninhabited islands, by specifically comparing the traditional approach of using rodenticides with sex-biasing gene drives. Concurrently the International Union for Conservation of Nature is assessing the risks and value of gene drives in general for conservation. Hence, we make the case that the ethical challenges with the use of gene drive sex-biasing techniques and the effectiveness of this tool will rely as much on its public acceptance and its democratic use as the actual science used to construct the technology.

Anticoagulant Rodenticides, Islands and Animal Welfare Accountancy.

Simple SummaryAnticoagulant rodenticides are a mainstay of rodent management in many domestic, municipal, agricultural, and conservation settings. Anticoagulant poisoning has poor welfare outcomes for mammals and birds and, worldwide, this means potentially very large numbers of animals are poisoned annually consequent (intended or not) to rodenticide use. Critical differences in use patterns of anticoagulants applied for ongoing rodent control, versus application for rodent eradication especially on islands, have clear implications for animal welfare costs measured as cumulative number of animals affected over time. Here we outline these differences and discuss how animal welfare considerations can be weighed in decisions to use anticoagulant rodenticides for island eradication attempts.Anticoagulant rodenticides are used to manage rodents in domestic, municipal, agricultural, and conservation settings. In mammals and birds, anticoagulant poisoning causes extensive hemorrhagic disruption, with the primary cause of death being severe internal bleeding occurring over days. The combined severity and duration of these effects represent poor welfare outcomes for poisoned animals. Noting a lack of formal estimates of numbers of rodents and nontarget animals killed by anticoagulant poisoning, the ready availability and worldwide use of anticoagulants suggest that very large numbers of animals are affected globally. Scrutiny of this rodent control method from scientific, public, and regulatory perspectives is being driven largely by mounting evidence of environmental transfer of residual anticoagulants resulting in harmful exposure in wild or domestic animals, but there is also nascent concern for the welfare of targeted rodents. Rodent control incurs a cumulative ledger of animal welfare costs over time as target populations reduced by poisoning eventually recover to an extent requiring another reduction. This ‘rolling toll’ presents a critical contrast to the animal welfare accountancy ledger for eradication scenarios, where rodent populations can be completely removed by methods including anticoagulant use and then kept from coming back (e.g., on islands). Successful eradications remove any future need to control rodents and to incur the associated animal welfare costs.

Preventing the Extinction of the Lord Howe Woodhen (Hypotaenidia sylvestris) through Predator Eradication and Population Augmentation

The Lord Howe Woodhen (Hypotaenidia sylvestris) is endemic to Lord Howe Island off the mid-east coast of Australia and came perilously close to extinction as a result of hunting pressure and introduced predators. A recovery program was implemented in the 1970s to reverse the decline of the species through eradicating introduced predators (pigs, cats and goats) and augmenting the population through an in situ captive-breeding program. In 1980, three wild breeding pairs were taken into captivity from Mount Gower. Over the four years of the captive-breeding program, 76 chicks were produced from the original founders and their progeny and an additional four chicks were artificially reared from eggs collected from a wild pair. Almost all woodhens were liberated across four release sites, but only 13% of released birds were resighted and numbers increased at only one of these sites and then declined. A captive-bred female that was released into the lowlands paired with a wild male (which had been temporarily held in captivity) and bred prolifically, leading to rapid population growth in the lowlands. The subpopulation on Mount Gower increased fivefold in the decade following the captive-breeding program, despite the removal of the three breeding pairs (which were released elsewhere) and receiving no augmentation from the captive-breeding program. The woodhen population continues to expand and it is likely the eradication of invasive rodents from Lord Howe Island during 2019 will facilitate further population growth.

Assessing gaps in reporting non-target mortality in island rodent eradication operations

Eradicating invasive species is a key part of island restoration, and can reverse the devastating impacts on native biota. Rodents are one of the most widespread invasive species, found on 80% of oceanic island systems, but have been removed from hundreds of islands through the application of anticoagulant-treated cereal bait. While such eradication operations are often net positive events for island ecosystems over the long-term, some native biota are also susceptible, resulting in short-term non-target mortality. One of the most widely distributed groups of birds, rails and allies (Rallidae) are highly adaptable, often endemic, and are known often to suffer mortality during rodent eradication operations, to varying degrees. Our goal was determine if the year of eradication or the size of the island predicted whether non-target mortalities were reported, including those that were true absences of mortality. We examined 122 eradication operations on 81 islands with rails present from 1983 to 2015, and found 78% with no reported information on non-target mortality using our search criteria. We found non-target mortality reporting has decreased over time, and there was no relationship with island size. Post-operational monitoring of eradication operations should thoroughly record non-target mortality to improve our understanding of factors affecting non-target mortality, and the efficacy of mitigation measures.

Diagnosing and responding to causes of failure to eradicate invasive rodents

Eradicating invasive rodents from islands is a common and powerful tool for conserving and restoring island ecosystems and populations. However, a variety of practical and ecological factors make rodent eradications susceptible to several different types of failure. If an eradication operation is not successful, we are faced with many difficult decisions on how best to proceed, particularly whether to continue actions or to wait before attempting eradication again. We can pro-actively prepare for the possibility of failure by developing failure response plans during the operational planning stages. A well-developed failure response plan includes data collection processes necessary to identify correctly the type of failure: (1) an incomplete eradication effort, (2) eradication effort complete, but individuals survived, or (3) rapid recolonization resulting from a breach of biosecurity measures. Data are also needed to meet pre-determined criteria to inform the decision when to reattempt eradication efforts, should an eradication fail. We provide a general conceptual framework for implementing failure response plans as a means of focusing limited conservation resources by expediently identifying the type of failure, reducing monitoring time-lines to determine if an eradication failed, identifying targets for when follow-up eradication efforts will be most successful, and if appropriate, modifying and updating biosecurity measures. Adopting this approach to pre-empt rodent eradication failures allows the island restoration community to maximize learning, base decision criteria on scientific evidence, and create a transparent decision-making process, thereby improving future eradication efforts.

Sustainability as a Framework for Considering Gene Drive Mice for Invasive Rodent Eradication

Gene drives represent a dynamic and controversial set of technologies with applications that range from mosquito control to the conservation of biological diversity on islands. Currently, gene drives are being developed in mice that may one day serve as an important tool for reducing invasive rodent pests, a key threat to island biodiversity and economies. Gene drives in mice are still in development in laboratories, and wild release of modified mice is likely a distant reality. However, technological changes outpace the existing capacity of regulatory frameworks, and thus require integrated governance frameworks. We suggest sustainability—which gives equal consideration to the environment, economy, and society—as one framework for addressing complexity and uncertainty in the governance of emerging gene drive technologies for invasive species management. We explore the impacts of rodent gene drives on island environments, including potential conservation and restoration of island biodiversity. We outline considerations for rodent gene drives on island economies, including impacts on agricultural and tourism losses, and reductions in biosecurity costs. Finally, we address the social dimension as an essential space for deliberation that will be integral to evaluating the potential deployment of gene drive rodents on islands.

International news media framing of invasive rodent eradications

Invasive rodents threaten global island biodiversity and have been eradicated from hundreds of islands. Eradication efforts can be contentious due to animal welfare concerns and risk to non-target species. The news media plays a critical role by providing context for eradications. To better understand how the news media frame invasive rodent eradications, we conducted a thematic content analysis of 462 newspaper articles published in newspapers from 13 countries between 1993 and 2014. Although the media typically frames environmental stories as conflicts between stakeholders, the media tended to use “conquest frames” for rodent eradications. Articles often emphasized key elements of the conquest frame, including recast rules and norms, being on frontiers, positioning heroes against nature, creating drama by questioning the success of heroes, orienting towards the future, and positioning the audience as an awestruck witness. We detected international differences for some themes. Articles from Canada and Australia often included costs of eradication, articles from New Zealand were less likely to include endemic species, and articles from the United States were most likely to include conflict. Our results suggest that unique aspects of rodent eradications may encourage conquest framing, and cultural contexts of place shape framing between countries. We conclude that conquest framing by the media has largely supported rodent eradication efforts on islands, but that may change when new eradication methods are developed or when eradications are planned for islands with human populations.

Evaluating the susceptibility of invasive black rats (Rattus rattus) and house mice (Mus musculus) to brodifacoum as a prelude to rodent eradication on Lord Howe Island

The use of anticoagulant rodenticides to eradicate invasive rodents from islands has become a powerful tool to prevent species extinctions and to restore degraded ecosystems. Success is dependent on all targeted individuals consuming rodenticide and dying as a result. Because susceptibility to anticoagulants can vary among rodent populations, it is important when planning an eradication to understand the efficacy of the proposed rodenticide on the target animals, particularly where there has been historic exposure to anticoagulants. The aims of this study were to investigate brodifacoum-susceptibility of black rats Rattus rattus and house mice Mus musculus on Lord Howe Island (LHI), Australia, where an eradication program is being planned. Black rats and house mice were subjected to various dosages of brodifacoum in a series of laboratory feeding trials. The results showed that rats on LHI died after consuming doses of rodenticide within expected ranges (60% died at 0.5 mg kg−1 and 100% died at 0.8 mg kg−1) when exposed to bait for 24 h. Mice, on the other hand, were more tolerant of the rodenticide, with 82% of individuals surviving doses of up to 2.0 mg kg−1 consumed over 24 h and some individuals needing 6.0 mg kg−1 consumed over 4 days to ingest a lethal dose. A laboratory experiment designed to simulate field application showed that all mice tested succumbed to brodifacoum poisoning when given the opportunity to consume sufficient bait (at least 6 days of exposure to toxic bait), although some individuals took 22 days to die. The results of these studies will help inform the Lord Howe Island rodent eradication.

World's Largest Rodent Eradication Project a Success: South Georgia Declared Rodent-free!

World's Largest Rodent Eradication Project a Success: South Georgia Declared Rodent-free!

Population status of four endemic land bird species after an unsuccessful rodent eradication on Henderson Island

SummaryInvasive rodents detrimentally affect native bird species on many islands worldwide, and rodent eradication is a useful tool to safeguard endemic and threatened species. However, especially on tropical islands, rodent eradications can fail for various reasons, and it is unclear whether the temporary reduction of a rodent population during an unsuccessful eradication operation has beneficial effects on native birds. Here we examine the response of four endemic land bird species on subtropical Henderson Island in the Pitcairn Island Group, South Pacific Ocean, following an unsuccessful rodent eradication in 2011. We conducted point counts at 25 sampling locations in 14 survey periods between 2011 and 2015, and modelled the abundance trends of all species using binomial mixture models accounting for observer and environmental variation in detection probability. Henderson Reed Warbler Acrocephalus taiti more than doubled in abundance (2015 population estimate: 7,194-28,776), and Henderson Fruit Dove Ptilinopus insularis increased slightly between 2011 and 2015 (2015 population estimate: 4,476–10,072), while we detected no change in abundance of the Henderson Lorikeet Vini stepheni (2015 population estimate: 554–3014). Henderson Crake Zapornia atra increased to pre-eradication levels following anticipated mortality during the operation (2015 population estimate: 4,960–20,783). A temporary reduction of rat predation pressure and rat competition for fruit may have benefitted the reed warbler and the fruit dove, respectively. However, a long drought may have naturally suppressed bird populations prior to the rat eradication operation in 2011, potentially confounding the effects of temporary rat reduction and natural recovery. We therefore cannot unequivocally ascribe the population recovery to the temporary reduction of the rat population. We encourage robust monitoring of island biodiversity both before and after any management operation to better understand responses of endemic species to failed or successful operations.

Conservationists Unleash Rodent Detection Dogs in Final Phase of World's Largest Rodent Eradication

Conservationists Unleash Rodent Detection Dogs in Final Phase of World's Largest Rodent Eradication

Corrigendum to: Rodent management issues in South Pacific islands: a review with case studies from Papua New Guinea and Vanuatu

Rodents are a key pest to agricultural and rural island communities of the South Pacific, but there is limited information of their impact on the crops and livelihoods of small-scale farmers. The rodent pest community is known, but the type and scales of damage to different crops on different islands are unknown. Knowledge about rodent pest management in other geographical regions may not be directly transferable to the Pacific region. Many studies on islands have largely focussed on the eradication of rodents from uninhabited islands for conservation benefits. These broadscale eradication efforts are unlikely to translate to inhabited islands because of complex social and agricultural issues. The livelihoods, culture and customs of poor small-scale farmers in the South Pacific have a large bearing on the current management of rodents. The aim of the present review was to describe the rodent problems, impacts and management of rodents on South Pacific islands, and identify gaps for further research. We compared and contrasted two case studies. The situation in Papua New Guinea is emergent as several introduced rodent species are actively invading new areas with wide-ranging implications for human livelihoods and conservation. In Vanuatu, we show how rodent damage on cocoa plantations can be reduced by good orchard hygiene through pruning and weeding, which also has benefits for the management of black pod disease. We conclude that (1) damage levels are unknown and unreported, (2) the impacts on human health are unknown, (3) the relationships between the pest species and their food sources, breeding and movements are not known, and (4) the situation in Papua New Guinea may represent an emergent crisis that warrants further investigation. In addition, there is a need for greater understanding of the invasive history of pest rodents, so as to integrate biological information with management strategies. Ecologically based rodent management can be achieved on Pacific Islands, but only after significant well funded large-scale projects are established and rodent ecologists are trained. We can learn from experiences from other locations such as Southeast Asia to guide the way.

Climate change leads to increasing population density and impacts of a key island invader

The considerable threats of invasive rodents to island biodiversity are likely to be compounded by climate change. Forecasts for such interactions have been most pronounced for the Southern Ocean islands where ameliorating conditions are expected to decrease thermal and resource restrictions on rodents. Firm evidence for changing rodent populations in response to climate change, and demonstrations of associated impacts on the terrestrial environment, are nonetheless entirely absent for the region. Using data collected over three decades on sub-Antarctic Marion Island, we tested empirically whether mouse populations have changed through time and whether these changes can be associated significantly with changing abiotic conditions. Changes in invertebrate populations, which have previously been attributed to mouse predation, but with little explicit demographic analysis, were also examined to determine whether they can be associated with changing mouse populations. The total number of mice on the island at annual peak density increased by 430.0% between 1979-1980 and 2008-2011. This increase was due to an advanced breeding season, which was robustly related to the number of precipitation-free days during the non-breeding season. Mice directly reduced invertebrate densities, with biomass losses of up to two orders of magnitude in some habitats. Such invertebrate declines are expected to have significant consequences for ecosystem processes over the long term. Our results demonstrate that as climate change continues to create ameliorating conditions for invasive rodents on sub-Antarctic islands, the severity of their impacts will increase. They also emphasize the importance of rodent eradication for the restoration of invaded islands.

Developing gene drive technologies to eradicate invasive rodents from islands

ABSTRACTIsland ecosystems are highly threatened by invasive rats and mice. Currently, the only effective technology for eradicating rodents from islands is toxicants. Though effective, they are expensive and have high failure rates. They are not species-specific and are potentially dangerous to humans. Gene drive technology is one alternative to toxicants for rodent eradication. Gene drive methods of rodent eradication offer an alternative to killing that has the potential to be more species-specific, more humane, and more biologically safe for use around humans. Technologies in development aim to apply either natural meiotic drive or clustered regularly interspersed short palindromic repeats to influence offspring development so that all offspring are phenotypically male, eventually creating a population that is not reproductively viable. Implementing this technology would involve releasing laboratory-developed engineered mice into wild populations. Some areas for further research include assessing the ecological effects of releasing engineered mice, the potential risks for the accidental or deliberate release of genetically modified organisms into mainland mouse populations, and the social, ethical, and regulatory acceptability of the technology.

Floreana Island re-colonization potential of the Galápagos short-eared owl (Asio flammeus galapagoensis)

Non-native invasive species threaten Galapagos’ endemic biodiversity, and increasing efforts are underway to protect its species from further harm. One such project is focused on the eradication of invasive rodents using rodenticide bait on Floreana, the archipelago’s sixth largest island. Short-eared owls (Asio flammeus galapagoensis) that consume poisoned rodents will, therefore, be at risk of secondary poisoning. If negatively impacted, it is not known to what degree the Floreana Island short-earned owl population is isolated, and whether potential re-colonization exists from its closest neighboring large population on Santa Cruz. Based on eight microsatellite loci and mtDNA control region sequence data from museum and contemporary samples, the short-eared owl populations on Floreana and Santa Cruz are not isolated from each other. However, gene flow is asymmetric from Floreana to Santa Cruz and not in the opposite direction. Morphometric data, including tarsus and bill size, and behavioral observations corroborate the genetic results and suggest that the Floreana population may possess unique traits compared to neighboring populations. For example, Floreana short-eared owls are more crepuscular than neighboring islands, which are predominately nocturnal, and were also non-responsive to inter-island call back recordings. Therefore, these results have important management implications concerning short-eared owl persistence on Floreana following rodenticide application. We recommend that managers implement additional precautions to protect the short-eared owl population until the risk of secondary poisoning has passed such as maintaining individuals in captivity. This study provides no evidence to suggest that short-eared owls are likely to disperse from Floreana’s closest large population on Santa Cruz if the local population is negatively impacted by rodenticide exposure, and the observed morphological and behavioral traits argue against translocating owls between islands.

Rodent eradication scaled up: clearing rats and mice from South Georgia

AbstractThe Subantarctic island of South Georgia lost most of its birds to predation by rodents introduced by people over 2 centuries. In 2011 a UK charity began to clear brown ratsRattus norvegicusand house miceMus musculusfrom the 170 km long, 3,500 km2island using helicopters to spread bait containing Brodifacoum as the active ingredient. South Georgia's larger glaciers were barriers to rodent movement, resulting in numerous independent sub-island populations. The eradication could therefore be spread over multiple seasons, giving time to evaluate results before recommencing, and also reducing the impact of non-target mortality across the island as a whole. Eradication success was achieved in the 128 km2Phase 1 trial operation. Work in 2013 (Phase 2) and early 2015 (Phase 3) covered the remaining 940 km2occupied by rodents. By July 2017, 28 months after baiting was concluded, there was no sign of surviving rodents, other than one apparently newly introduced by ship in October 2014. A survey using detection dogs and passive devices will search the Phase 2 and Phase 3 land for rodents in early 2018. Seven (of 30) species of breeding birds suffered losses from poisoning, but all populations appear to have recovered within 5 years. The endemic South Georgia pipitAnthus antarcticuswas the first bird to breed in newly rat-free areas, but there were also signs that cavity-nesting seabirds were exploring scree habitat denied them for generations. Enhanced biosecurity measures on South Georgia are needed urgently to prevent rodents being reintroduced.

Costs and Benefits of Rodent Eradication on Lord Howe Island, Australia

Costs and Benefits of Rodent Eradication on Lord Howe Island, Australia

Rodent eradications as ecosystem experiments: a case study from the Mexican tropics

For effective and efficient pest management it is essential to understand the ecology of the target species and recipient ecosystems. The use of rodent eradication as a restoration tool is well established in temperate regions, but less common in the tropics, presenting an opportunity to undertake scientific learning in tandem with rodent eradications. On a dry tropical archipelago, we used a Before-After-Control-Impact framework to document (1) fluctuations in the abundance and demography of invasive Rattus rattus and Mus musculus on three different islands, (2) the trophic niche of all three invasive rodent populations, and (3) changes in the invertebrate community before and after rodent eradication, also comparing with two rodent free islands. While rat density was high and relatively stable throughout the year, the two mouse populations greatly differed in body size and seasonal dynamics, despite their proximity. The rodents in all three populations were generalist and opportunistic feeders, although stable isotope analyses results indicated major differences among them, driven by food availability and rodent species. Seasonal fluctuations in invertebrate communities depended on rodent invasion status, but recovery in the invertebrate communities one year after rodent removal was limited for all islands. Predictions for other tropical ecosystem biomes require long-term research on more tropical islands. Improving our understanding of island and species-specific contexts of rodent eradications can advance island restoration projects and assist the selection of indicator species for ecosystem recovery.