Eradicating multiple invasive species on inhabited islands: the next big step in island restoration?

Invasive species are the greatest threat to island ecosystems, which harbour nearly half the world’s endangered biodiversity. However, eradication is more feasible on islands than on continents. We present a global analysis of 1,224 successful eradications of invasive plants and animals on 808 islands. Most involve single vertebrate species on uninhabited islands, but plant and invertebrate eradications occur more often on inhabited islands. Inhabited islands are often highly modified and support numerous introduced species. Consequently, targeting a single invasive species can be ineffective or counterproductive. The impacts of other pests will continue and, in some cases, be exacerbated. The presence of people also creates regulatory, logistical and socio-political constraints. Real or perceived health risks to inhabitants, pets and livestock may restrict the use of some eradication tools, and communities or individuals sometimes oppose eradication. Despite such challenges, managing invasive species is vital to conserve and restore the unique biodiversity of many inhabited islands, and to maintain or improve the welfare and livelihoods of island residents. We present a brief case study of the Juan Fernández Archipelago, Chile, and discuss the feasibility of eradicating large suites of invasive plants and animals from inhabited islands while managing other invaders for which eradication is not feasible or desirable. Eradications must be planned to account for species interactions. Monitoring and contingency plans must detect and address any ‘surprise effects’. Above all, it is important that the local community derives social, cultural and/or economic benefits, and that people support and are engaged in the restoration effort.     

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

Invasive 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.     

Costing eradications of alien mammals from islands

The ability to estimate costs of alien species eradications is essential for a rigorous assessment of priorities for island restoration. Using a global data file from 41 islands, mostly gleaned from the 'grey' literature, we show that the cost of vertebrate eradications can be satisfactorily predicted if island area and species to be eradicated are known. About 72% of the variation in cost can be explained by island area, whereas, for a given area, rodent eradications are 1.7–3.0 times more expensive than ungulate eradications. Costs per hectare decrease with island size. Restricting the analysis to roughly half the data set, the relatively homogeneous half concerned with New Zealand islands, we identify two further influences on cost: date of eradication and distance to the main airport (an indicator of remoteness). For a given area, costs have declined over time but increase with island remoteness. This information therefore provides conservation planners with a robust, if preliminary, estimate of the cost of any proposed eradication programme.     

Bio-Economics of Large-Scale Eradication of Feral Goats From Santiago Island,Galápagos

ABSTRACT Invasive mammals are premier drivers of extinction and ecosystem change, particularly on islands. In the 1960s, conservation practitioners started developing techniques to eradicate invasive mammal populations from islands. Larger and more biologically complex islands are being targeted for restoration worldwide. We conducted a feral goat (Capra hircus) eradication campaign on Santiago Island in the Galápagos archipelago, which was an unprecedented advance in the ability to reverse biodiversity impacts by invasive species. We removed >79,000 goats from Santiago Island (58,465 ha) in <4.5 years, at an approximate cost of US$6.1 million. An eradication ethic combined with a suite of techniques and technologies made eradication possible. A field-based Geographic Information System facilitated an adaptive management strategy, including adjustment and integration of hunting methods. Specialized ground hunting techniques with dogs removed most of the goat population. Aerial hunting by helicopter and Judas goat techniques were also critical. Mata Hari goats, sterilized female Judas goats induced into a long-term estrus, removed males from the remnant feral population at an elevated rate, which likely decreased the length and cost of the eradication campaign. The last 1,000 goats cost US$2.0 million to remove; we spent an additional US$467,064 on monitoring to confirm eradication. Aerial hunting is cost-effective even in countries where labor is inexpensive. Local sociopolitical environments and best practices emerging from large-scale, fast-paced eradications should drive future strategies. For nonnative ungulate eradications, island size is arguably no longer the limiting factor. Future challenges will involve removing invasive mammals from large inhabited islands while increasing cost-effectiveness of removing low-density populations and confirming eradication. Those challenges will require leveraging technology and applying theory from other disciplines, along with conservation practitioners working alongside sociologists and educators.     

Long-term effects of feral goats (<Emphasis Type="Italic">Capra hircus</Emphasis>) on Mediterranean island communities: results from whole island manipulations

Islands exhibit disproportionally high biodiversity, however high levels of endemism and simplified food webs make their communities susceptible to invasive species. Introduced goats (Capra hircus), a generalist herbivore, are among the most harmful invasive species on islands. Concern about goat impacts on island communities have resulted in eradication programs, which have been generally implemented without comprehensive evaluation and monitoring. Unintended consequences may follow eradication, as grazing can have complex effects on island food webs. Using whole island manipulations, we evaluate the long-term, community-wide effects of goat herbivory, as well as their subsequent removal, in a system of 16 islands in the Aegean Sea (Greece) located within the Mediterranean biodiversity hotspot. Goat grazing on these islands is a major conservation concern, as these support endemic plant communities that have evolved in low herbivory conditions and lack appropriate defenses. We show that goat introductions lead to significant decreases in vegetation height, percent cover, and biomass but not to immediate plant species loss, as native island endemics are replaced with widespread generalist taxa carried in by the livestock. Additionally, goats contribute to the desertification of islands by initiating a long-term soil loss cycle that continues even after goats are removed; however, remaining soil structure and chemistry are not affected. Island arthropod populations do not appear to be significantly impacted by goat introduction or removal, except for a distinct increase in the order Diptera with goat presence. This study also reaffirms the role of seabirds in providing important marine subsidies, rich in nitrogen and phosphorus, to island food webs. Plant species diversity declines following goat removal, and vegetation cover returns only partially, as further recovery is being prevented by the long-term loss of soil. This suggests that following goat removal, island communities may require additional restoration efforts, including seabird reestablishment and reintroduction of extirpated plant populations, to promote island recovery.     

A review of mammal eradications on Mediterranean islands

1. Impacts of alien invasive species on island communities and ecosystems may be even more detrimental than on the mainland. Therefore, since the 1950s, hundreds of restoration projects have been implemented worldwide, with the aim of controlling or eradicating alien species from islands. To date, no review has been focused on eradication on Mediterranean islands. To fill the gap, I reviewed the available information concerning mammal eradications so far carried out on Mediterranean islands, examining the details of several aspects of project implementation and monitoring.
2. I obtained data for 139 attempted eradications on 107 Mediterranean islands in eight countries, with Greece, Italy, and Spain accounting for the highest number. Eradication projects targeted 13 mammal species. The black rat Rattus rattus was the target of over 75% of the known attempted eradications in the Mediterranean Basin; other species targeted were feral goat Capra hircus, house mouse Mus musculus, European rabbit Oryctolagus cuniculus, and domestic cat Felis catus. The most widely adopted technique was poisoning (77% of all eradications), followed by trapping (15%) and hunting (4%). However, techniques were largely target-specific.
3. The average failure rate was about 11%. However, this percentage varied according to the specific mammalian order, and eradications of Carnivora failed more often than those of other mammals. Among rodents, house mouse eradication attained a very high failure rate (75%). Reinvasion occurred after 15% of successful eradications.
4. A better understanding of the motivations of animal rights activists may improve the chance of success when eradicating charismatic or domesticated species. Furthermore, it is crucial to collect data and case studies about reinvasions, in order to strengthen biosecurity programmes following eradication. As in other parts of the world, the next frontier in alien mammal management on Mediterranean islands concerns the eradication of invasive species from inhabited islands.

     

Deciding when to lend a helping hand: a decision-making framework for seabird island restoration

Following the removal of an introduced species, island restoration can follow two general approaches: passive, where no further intervention occurs and the island is assumed to recover naturally, and; active, where recovery of key taxa (e.g. seabirds) is enhanced by manipulating movement and demography. Steps for deciding between these techniques are: (1) outlining an explicit restoration goal; (2) building a conceptual model of the system; (3) identifying the most effective management approach; and (4) implementing and monitoring outcomes. After decades of island restoration initiatives, retrospective analysis of species’ responses to active and passive management approaches is now feasible. We summarize the advantages of incorporating these analyses of past restoration results as an initial step in the decision-making process. We illustrate this process using lessons learned from the restoration of seabird-driven island ecosystems after introduced vertebrate eradication in New Zealand. Throughout seven decades of successful vertebrate eradication projects, the goals of island restoration have shifted from passive to active enhancement of island communities, which are heavily dependent on burrow-nesting petrel population recovery. Using a comparative analysis of petrel response to past predator eradications we built a conceptual model of petrel recovery dynamics and defined key site and species characteristics for use in a stepwise decision tree to select between active or passive seabird population management. Active restoration techniques should be implemented when seabird populations are absent or declining; and on islands with no nearby source colony, small remnant colonies, highly altered habitat with shallow soil and slopes, and with competitive species pairs. As we continue to restore complex island communities, decision-making tools using a logical, step-wise framework informed by previous restoration successes and failures can aid in increasing understanding of ecosystem response.     

A GIS‐based decision‐making approach for prioritizing seabird management following predator eradication

Given that 29% of seabird species are threatened with extinction, protecting seabird colonies on offshore islands is a global conservation priority. Seabirds are vulnerable to non‐native predator invasions, which reduce or eliminate colonies. Accordingly, conservation efforts have focused on predator eradication. However, affected populations are often left to passively recover following eradications. Although seabirds are highly mobile, their life history traits such as philopatry can limit passive recolonization of newly predator‐free habitat. In such cases, seabird colonies can potentially be re‐instated with active restoration via chick translocations or social attraction methods, which can be risky and expensive. We used biogeographic and species‐specific behavioral data in the Hauraki Gulf, New Zealand, a global hotspot of seabird diversity and predator eradications, to illustrate the use of geographic information systems multi‐criteria decision analysis to prioritize islands for active seabird restoration. We identified nine islands with low observed passive recovery of seabirds posteradication over a 50‐year timeframe, and classified these as sites where active seabird management could be prioritized. Such spatially explicit tools are flexible, allowing for managers to choose case‐specific criteria such as time, funding, and goals constrained for their conservation needs. Furthermore, this flexibility can also be applied to threatened species management by customizing the decision criteria for individual species' capacity to passively recolonize islands. On islands with complex restoration challenges, decision tools that help island restoration practitioners decide whether active seabird management should be paired with eradication can optimize restoration outcomes and ecosystem recovery.     

Integrating seabird restoration and mammal eradication programs on islands to maximize conservation gains

Colonial nesting seabirds frequently drive island ecosystem biodiversity by maintaining ecosystem functioning and community dynamics. Invasive mammal introductions to most of the world’s islands have ravaged insular seabird populations and had associated devastating ecosystem-wide effects. Eradication programs remove invasive mammals from islands, with the goal of conserving and restoring island species and systems. However, most eradication programs rely almost exclusively on passive seabird recovery to achieve these goals. Unfortunately, the life histories of most seabird species are not conducive to passive recovery within a contemporary timeframe. Seabird restoration techniques can effectively overcome life history related issues and significantly reduce recovery times for insular seabird populations, thereby reducing associated ecosystem-wide recovery times. By integrating seabird restoration and eradication programs, practitioners can maximize conservation gains, expand funding opportunities, and restore island ecosystems and the biodiversity they support.     

Prioritizing the world's islands for vertebrate-eradication programmes

In the last 400 years, more species have become extinct on small islands than on continents. Yet, scant attention has hitherto been paid to prioritizing island restorations. Nevertheless, considerable conservation effort is now devoted to removing a major cause of these extinctions – invasive alien vertebrates. Because modern techniques allow the clearance of invasive vertebrates from quite large islands (up to 1000 km²), many islands are candidates for restoration. A robust strategy for allocating available funds is urgently needed. It requires, for each candidate island, an objective estimation of conservation gain and a method for predicting its financial cost. Our earlier work showed that a good first-pass estimate of vertebrate eradication costs can be made using just island area and target species. Costs increase with island area, while rodents are more expensive per unit area than ungulates. Here, we develop a method for assessing the conservation benefit of a proposed eradication and apply the method to threatened birds, but not other taxa. The method, combining information on how threatened a species is, on the impact of alien vertebrates on that species and on the islands on which the species occurs, allows us to present a means of determining which islands yield the greatest conservation benefit per unit of expenditure on vertebrate eradication. In general, although greater overall benefit would accrue to birds from eradication of invasive vertebrates on larger islands, benefit per unit of expenditure is the highest on relatively small islands, and we identify those that should be priority targets for future eradications. Crucially, this quantitative assessment provides considerable efficiency gains over more opportunistic targeting of islands. The method could be adapted to prioritize islands on a regional or national basis, or with different conservation gains in mind.     

The effects of hydramethylnon on the tropical fire ant, <Emphasis Type="Italic">Solenopsis geminata</Emphasis> (Hymenoptera: Formicidae), and non-target arthropods on Spit Island,Midway Atoll,Hawaii

Invasive ants can cause major disruptions in native ecosystems. Ant eradication methods without significant non-target effects are needed to stop incipient invasions and to aid in ecosystem restoration. Successful ant eradications are rare and there is very little understanding of the effects of ant eradication methods, such as the use of formicides, on non-target species. Here we attempted to control and possibly eradicate the invasive tropical fire ant, Solenopsis geminata, from a small islet using the formicide Maxforce^® (active ingredient: hydramethylnon), and to quantify the non-target effects on an almost exclusively alien ground-dwelling arthropod community. S. geminata abundance was reduced and the species was not detected on bait cards for 12 months post-treatment. The abundance of another non-target invasive ant that was primarily detected in pitfall traps, Tetramoruim bicarinatum, declined in pitfall traps following treatment, but seemed to be excluded from bait cards by S. geminata. Total ant abundance did not return to original levels until more than 12 months post-treatment. Populations of alien cockroaches (Order Blattaria) and crickets (Orthoptera: Gryllidae) were negatively affected by the treatment. We conclude that Maxforce^® can be used to control small infestations of S. geminata and T. bicarinatum effectively; however we recommend it be used cautiously due to the potential ecological cost to non-target species. Use in areas where infestations are small and isolated will maximize the likelihood of success while minimizing non-target effects.     

Winter ecology of house mice and the prospects for their eradication from Steeple Jason (Falkland Islands)

Invasive house mice Mus musculus are known to impact on seabird, invertebrate and plant communities on temperate and subantarctic islands, particularly where they are the sole rodent species. Steeple Jason, in the Falkland Islands, is an island which supports globally important seabird populations as well as introduced mice. To evaluate the prospects for mouse eradication, we investigated mouse ecology and undertook bait uptake trials on Steeple Jason in late winter. Mice were present in all habitats but were most abundant in tussac Poa flabellata where they occurred at 20–35 mice ha^?1. From 58 mature perforate females, 16 % were pregnant, with litters of 4–8 pups. The first lactating female was caught at the end of August, suggesting that breeding had recently begun. Bait trials replicating an aerial eradication were undertaken on two trapping grids of 7.7 and 6.8 ha, with non-toxic pellets containing the biomarker pyranine spread at 7.5–7.7 kg ha^?1. All 447 mice captured after baiting had consumed bait. The relatively low winter density, distribution and biology of house mice on Steeple Jason are similar to those observed before other successful mice eradications, and the study indicated 100 % bait acceptance. Before an eradication attempt, we suggest investigating whether breeding ceases completely earlier in the winter and urge careful consideration of non-target species.     

Stable isotope analysis as an early monitoring tool for community‐scale effects of rat eradication

Invasive rats have colonized most of the islands of the world, resulting in strong negative impacts on native biodiversity and on ecosystem functions. As prolific omnivores, invasive rats can cause local extirpation of a wide range of native species, with cascading consequences that can reshape communities and ecosystems. Eradication of rats on islands is now becoming a widespread approach to restore ecosystems, and many native island species show strong numerical responses to rat eradication. However, the effect of rat eradication on other consumers can extend beyond direct numerical effects, to changes in behavior, dietary composition, and other ecological parameters. These behavioral and trophic effects may have strong cascading impacts on the ecology of restored ecosystems, but they have rarely been examined. In this study, we explore how rat eradication has affected the trophic ecology of native land crab communities. Using stable isotope analysis of rats and crabs, we demonstrate that the diet or trophic position of most crabs changed subsequent to rat eradication. Combined with the numerical recovery of two carnivorous land crab species (Geograpsus spp.), this led to a dramatic widening of the crab trophic niche following rat eradication. Given the established importance of land crabs in structuring island communities, particularly plants, this suggests an unappreciated mechanism by which rat eradication may alter island ecology. This study also demonstrates the potential for stable isotope analysis as a complementary monitoring tool to traditional techniques, with the potential to provide more nuanced assessments of the community‐ and ecosystem‐wide effects of restoration.     

Geographic Tools for Eradication Programs of Insular Non-native Mammals

Non-native mammals are major drivers of ecosystem change and biodiversity loss; this is especially apparent on islands. However, techniques exist to remove non-native mammals, providing a powerful conservation tool. Conservation practitioners are now targeting larger islands for restoration. Leveraging existing and developing new techniques and technologies will prove critical to successful eradications on large islands. Using the removal of introduced goats (Capra hircus) from Santiago Island, Galápagos as a case study, we present a suite of Geographic Information System (GIS) tools that aid island conservation actions. GIS tools were incorporated into the three phases of the eradication campaign: planning, hunting, and monitoring. Further, these tools were adopted for three eradication techniques: ground-based hunting, aerial hunting by helicopter, and Judas goats. These geographic approaches provide a foundation for statistical, spatial, and economic analyses that should increase the capability and efficiency of removal campaigns. Given limited conservation funds and the dire status of many insular species, efficiently removing non-native mammals from islands is of paramount global conservation importance.     

Identifying eradication units in an invasive mammalian pest species

Eradication of invasive species is an important component for species conservation and ecosystem restoration. Success of eradications is dependent on knowledge of population connectivity in order to determine reinvasion pathways, and hence populations requiring simultaneous eradication (eradication units). The common brushtail possum (Trichosurus vulpecula) was introduced into New Zealand from Australia and Tasmania, and now occupies a wide range of habitats across the majority of New Zealand. Possums are one of the most destructive invaders within New Zealand, with extensive control operations occurring throughout the country. Understanding the population connectivity of possums on mainland New Zealand (North and South Islands) will enhance the success of planned eradications. We examined the genetic population structure of invasive possums to identify gene flow, thus reinvasion pathways, between seven populations around Dunedin and on the Otago Peninsula where eradication of possums is occurring. Genetic variation at 12 microsatellite loci was comparable between all sampled populations and exhibited a significant isolation by distance pattern. Bayesian clustering methods supported the existence of two population clusters, indicating the presence of a reinvasion pathway onto the Otago Peninsula from urban areas at the Southern end of the Peninsula. To avoid recolonisation, all possums on the Otago Peninsula should be eradicated simultaneously, with the implementation and ongoing maintenance and monitoring of an urban buffer zone. We recommend pre-eradication genetic analyses be adopted by all pest managers to define appropriate eradication units, thereby maximising eradication success and avoiding costly failures.     

Trophic niche changes associated with the eradication of invasive mammals in an insular lizard: an assessment using isotopes

Invasive species are a major threat to island biodiversity, and their eradications have substantially contributed to the conservation of island endemics. However, the consequences of eradications on the trophic ecology of native taxa are largely unexplored. Here, we used the eradication of invasive black rats Rattus rattus and European rabbits Oryctolagus cuniculus from the Berlenga Island, in the western coast of Portugal, as a whole-ecosystem experiment to investigate the effects of the eradication of invasive mammals on the trophic niche and body dimensions of the island-restricted Berlenga wall lizard Podarcis carbonelli berlengensis over a 2-year period. Our results suggest an expansion of the isotopic niche and an intensification of the sexual dimorphism of the lizard following mammal eradication. Additionally, we found considerable variability in isotopic niche across the island and detected evidence of sex-specific and season-modulated nutritional requirements of this threatened reptile. Our findings support that the eradication of 2 of the planet’s most problematic invasive vertebrates led to changes in the lizard trophic niche and sexual dimorphism in just 2 years. This suggests that the ecological pressures—for example, prey availability and habitat structure—to which lizards are exposed have substantially changed post-eradication. Our study emphasizes the scientific value of island eradications as experiments to address a wide range of ecological questions and adds to the increasing body of evidence supporting substantial conservation gains associated with these restoration interventions.     

Invasive species and land bird diversity on remote South Atlantic islands

Invasive species pose significant threats to biodiversity, especially on islands. They cause extinctions and population declines, yet little is known about their consequences on the emergent, metacommunity-level patterns of native species in island assemblages. We investigated differences in species–area relationships, nestedness, and occupancy of 9 species of native land birds between island assemblages with and without invasive Norway rats (Rattus norvegicus) in the Falkland Archipelago. We found that species–area curves, nestedness, and individual species’ occurrences differed between island assemblages with and without rats. Rat-free islands had, on average, 2.1 more land bird species than rat-infested islands of similar size. Passerine bird communities on islands with and without rats were significantly nested, but nestedness was significantly higher on rat-free islands than on rat-infested islands. The presence of rats was associated with differences in the incidence of many, but not all bird species. On rat free islands the occurrence of all species increased with island area. The occurrence of most, albeit not all, bird species was lower on islands with than on islands without rats. Two species of conservation concern, Troglodytes aedon cobbi and Cinclodes antarcticus, were abundant on rat-free islands, but absent or found at very low frequencies on islands with rats. The occurrence of three species was not associated with the presence of rats. The patterns presented here can be used to evaluate the consequences of ongoing rat eradications for passerine diversity, distribution, and abundance.     

Prioritising islands in the United Kingdom and crown dependencies for the eradication of invasive alien vertebrates and rodent biosecurity

Invasive alien vertebrates (IAVs) pose a significant threat to island biodiversity worldwide, and their removal is an important nature conservation management goal. As methods advance, eradications from larger islands and of multiple species simultaneously are increasingly undertaken. Effective targeting to maximise conservation gain is important given limited resources. We build on existing prioritisation methods and use the islands of the UK and Crown Dependencies (UK) as an example of how vertebrate eradications might be prioritised and invasive-free status maintained through biosecurity. For each of the 9688 UK islands, we assessed ecological importance for native vertebrates and the anticipated impacts of the IAVs present to estimate the benefit of restoration based on the feasibility and sustainability of IAV eradications in relation to island size, human population and risk of unassisted reinvasion by swimming. As reinvasion poses a threat to the long-term benefits of eradication, we incorporated species-specific swimming distances and explored the effects of varying reinvasion probability from risk-averse to higher-risk strategies. The 25 islands that would benefit most from eradications were in Scotland, Northern Ireland and the Channel Islands. Our prioritisation method should be seen as an initial guide to identify islands that might benefit from intervention when faced with a large list of potential sites. Feasibility studies taking account of factors such as interspecific interactions, anthropogenic reinvasion, views of residents or ‘social feasibility’ and cost need to be undertaken before planning any eradication. We prioritised biosecurity for rat-free islands to highlight where comprehensive measures might be most beneficial.     

Passive recovery of an island bird community after rodent eradication

The number and scale of island invasive species eradications is growing, but quantitative evidence of the conservation efficacy of passive recovery is limited. We compare relative abundances of breeding birds on Hawadax Island (formerly named Rat island), Aleutian Archipelago, Alaska, pre- and post- rat eradication to examine short-term (<1 year post-eradication) changes due to rodenticide application, and medium-term (5 years post-eradication) changes due to the absence of invasive rats. In the short term, Bald Eagle (Haliaeetus leucocephalus) numbers decreased from 24 individuals pre-eradication to two individuals <1 year post-eradication, but recovered to 10 individuals (42 % of pre-eradication) 5 years post-eradication, with all individuals nesting (63 % of the pre-eradication nesting). Five years post-eradication relative abundances of most terrestrial birds surveyed using point counts either significantly increased [Gray-crowned Rosy Finch (Leucosticte tephrocotis), Lapland Longspur (Calcarius lapponicus), Snow Bunting (Plectrophenax nivalis), Song Sparrow (Melospiza melodia)] or did not differ [Pacific Wren (Troglodytes troglodytes)]. Shorebirds also increased 5 years post-eradication with Black Oystercatchers (Haematopus palliates) increasing fivefold, and Rock Sandpiper (Calidris ptilocnemis) nesting increasing from one to five nests. We confirmed two species of ground nesting seabirds [Tufted Puffin (Fratercula cirrhata) and Leach’s Storm-petrel (Oceanodroma leucohoa)] as nesting (puffin) or engaged in courtship behavior (Storm-petrel) 5 years post-eradication. Our results indicate that despite the short-term impact on Bald Eagles, and without further human intervention, most terrestrial and marine birds have newly-colonized, re-colonized, or increased in abundance following the eradication of invasive rats.     

Archipelago-wide island restoration in the Galápagos Islands: reducing costs of invasive mammal eradication programs and reinvasion risk

Invasive alien mammals are the major driver of biodiversity loss and ecosystem degradation on islands. Over the past three decades, invasive mammal eradication from islands has become one of society's most powerful tools for preventing extinction of insular endemics and restoring insular ecosystems. As practitioners tackle larger islands for restoration, three factors will heavily influence success and outcomes: the degree of local support, the ability to mitigate for non-target impacts, and the ability to eradicate non-native species more cost-effectively. Investments in removing invasive species, however, must be weighed against the risk of reintroduction. One way to reduce reintroduction risks is to eradicate the target invasive species from an entire archipelago, and thus eliminate readily available sources. We illustrate the costs and benefits of this approach with the efforts to remove invasive goats from the Galápagos Islands. Project Isabela, the world's largest island restoration effort to date, removed >140,000 goats from >500,000 ha for a cost of US$10.5 million. Leveraging the capacity built during Project Isabela, and given that goat reintroductions have been common over the past decade, we implemented an archipelago-wide goat eradication strategy. Feral goats remain on three islands in the archipelago, and removal efforts are underway. Efforts on the Galápagos Islands demonstrate that for some species, island size is no longer the limiting factor with respect to eradication. Rather, bureaucratic processes, financing, political will, and stakeholder approval appear to be the new challenges. Eradication efforts have delivered a suite of biodiversity benefits that are in the process of revealing themselves. The costs of rectifying intentional reintroductions are high in terms of financial and human resources. Reducing the archipelago-wide goat density to low levels is a technical approach to reducing reintroduction risk in the short-term, and is being complemented with a longer-term social approach focused on education and governance.