Gregg R. Howald

Severity of the Effects of Invasive Rats on Seabirds : A Global Review

Invasive rats are some of the largest contributors to seabird extinction and endangerment worldwide. We conducted a meta-analysis of studies on seabird-rat interactions to examine which seabird phylogenetic, morphological, behavioral, and life history characteristics affect their susceptibility to invasive rats and to identify which rat species have had the largest impact on seabird mortality. We examined 94 manuscripts that demonstrated rat effects on seabirds. All studies combined resulted in 115 independent rat-seabird interactions on 61 islands or island chains with 75 species of seabirds in 10 families affected. Seabirds in the family Hydrobatidae and other small, burrow-nesting seabirds were most affected by invasive rats. Laridae and other large, ground-nesting seabirds were the least vulnerable to rats. Of the 3 species of invasive rats, Rattus rattus had the largest mean impact on seabirds followed by R. norvegicus and R. exulans; nevertheless, these differences were not statistically significant. Our findings should help managers and conservation practitioners prioritize selection of islands for rat eradication based on seabird life history traits, develop testable hypotheses for seabird response to rat eradication, provide justification for rat eradication campaigns, and identify suitable levels of response and prevention measures to rat invasion. Assessment of the effects of rats on seabirds can be improved by data derived from additional experimental studies, with emphasis on understudied seabird families such as Sulidae, Phalacrocoracidae, Spheniscidae, Fregatidae, Pelecanoididae, Phaethontidae, and Diomedeidae and evaluation of rat impacts in tropical regions.

Invasive mammal eradication on islands results in substantial conservation gains.

Significance Global conservation actions to prevent or slow extinctions and protect biodiversity are costly. However, few conservation actions have been evaluated for their efficacy globally, hampering the prioritization of conservation actions. Islands are key areas for biodiversity conservation because they are home to more than 15% of terrestrial species and more than one-third of critically endangered species; nearly two-thirds of recent extinctions were of island species. This research quantifies the benefits to native island fauna of removing invasive mammals from islands. Our results highlight the importance of this conservation measure for protecting the worlds most threatened species. More than US

High-impact Conservation: Invasive Mammal Eradications from the Islands of Western Mexico

21 billion is spent annually on biodiversity conservation. Despite their importance for preventing or slowing extinctions and preserving biodiversity, conservation interventions are rarely assessed systematically for their global impact. Islands house a disproportionately higher amount of biodiversity compared with mainlands, much of which is highly threatened with extinction. Indeed, island species make up nearly two-thirds of recent extinctions. Islands therefore are critical targets of conservation. We used an extensive literature and database review paired with expert interviews to estimate the global benefits of an increasingly used conservation action to stem biodiversity loss: eradication of invasive mammals on islands. We found 236 native terrestrial insular faunal species (596 populations) that benefitted through positive demographic and/or distributional responses from 251 eradications of invasive mammals on 181 islands. Seven native species (eight populations) were negatively impacted by invasive mammal eradication. Four threatened species had their International Union for the Conservation of Nature (IUCN) Red List extinction-risk categories reduced as a direct result of invasive mammal eradication, and no species moved to a higher extinction-risk category. We predict that 107 highly threatened birds, mammals, and reptiles on the IUCN Red List—6% of all these highly threatened species—likely have benefitted from invasive mammal eradications on islands. Because monitoring of eradication outcomes is sporadic and limited, the impacts of global eradications are likely greater than we report here. Our results highlight the importance of invasive mammal eradication on islands for protecting the worlds most imperiled fauna.

Eradication of black rats Rattus rattus from Anacapa Island

Abstract Islands harbor a disproportionate amount of the earths biodiversity, but a significant portion has been lost due in large part to the impacts of invasive mammals. Fortunately, invasive mammals can be routinely removed from islands, providing a powerful tool to prevent extinctions and restore ecosystems. Given that invasive mammals are still present on more than 80% of the worlds major islands groups and remain a premier threat to the earths biodiversity, it is important to disseminate replicable, scaleable models to eradicate invasive mammals from islands. We report on a successful model from western México during the past decade. A collaborative effort between nongovernmental organizations, academic biologists, Mexican government agencies, and local individuals has resulted in major restoration efforts in three island archipelagos. Forty-two populations of invasive mammals have been eradicated from 26 islands. For a cost of USD 21 615 per colony and USD 49 370 per taxon, 201 seabird colonies and 88 endemic terrestrial taxa have been protected, respectively. These conservation successes are a result of an operational model with three main components: i) a tri-national collaboration that integrates research, prioritization, financing, public education, policy work, capacity building, conservation action, monitoring, and evaluation; ii) proactive and dedicated natural resource management agencies; and iii) effective partnerships with academic researchers in México and the United States. What is now needed is a detailed plan to eradicate invasive mammals from the remaining islands in the region that integrates the needed additional financing, capacity, technical advances, and policy issues. Island conservation in western México provides an effective approach that can be readily applied to other archipelagos where conservation efforts have been limited.

Evaluating alternative rodenticides for island conservation: roof rat eradication from the San Jorge Islands, Mexico

Removing invasive rats from islands is a powerful conservation tool, and practitioners are now targeting larger islands for rat eradication. As they do so, they face the challenge of mitigating for potential non-target impacts on native biodiversity that may be susceptible to rodenticides. We report on the eradication of black rats Rattus rattus from Anacapa Island, California, in 2001–2002, which was the first-ever invasive rodent eradication from an entire island where an endemic rodent was present and the first aerial application of a rodenticide in North America. As a mitigation strategy we staggered the rodenticide application over 2 years and held a representative sample of the Anacapa deer mouse Peromyscus maniculatus anacapae in captivity. We also mitigated for bird species potentially susceptible to brodifacoum poisoning and monitored aspects of the terrestrial and marine environments. The free-ranging native rodent population severely declined following rodenticide applications but reintroduction and translocation efforts were successful, and the population quickly recovered to pre-eradication levels. Non-target impacts also included mortality of raptors, gulls and passerines, including high mortality of rufous-crowned sparrows Aimophila ruficeps obscura despite planned mitigation. All observed non-target impacts are expected to be ephemeral; however, further monitoring should reveal details on the dynamics of those impacts. Brodifacoum was not detected in the marine environment or in significant amounts in terrestrial soil, plants and arthropods. Seabird benefits from the rat eradication were quickly realized.

Predation of artificial Xantus's murrelet ( Synthliboramphus hypoleucus scrippsi ) nests before and after black rat ( Rattus rattus ) eradication

Introduced commensal rats (Rattus spp.) are a major contributor to the extinction and endangerment of island plants and animals. The use of the toxin brodifacoum to completely eradicate rats from islands is a powerful conservation tool. However, brodifacoum is toxic to animals other than rats and on some islands its use may not be feasible without prohibitively expensive mitigation. As part of a regional conservation program, we experimentally tested brodifacoum and two less toxic rodenticides, diphacinone and cholecalciferol, in eradicating Rattus rattus from three small islands in the northern Gulf of California, Mexico. All three rodenticides were successful in eradicating rats, suggesting that the less toxic diphacinone and cholecalciferol may be useful alternatives to brodifacoum for some island eradication programs. However, the choice of rodenticide must be balanced between efficacy and the risks to non-target species. Applied field research is needed on less toxic rodenticides, as well as improving palatability of baits. This may prove invaluable in preventing extinctions and in restoring larger and more diverse island ecosystems.

Response of Native Species 10 Years After Rat Eradication on Anacapa Island, California

SUMMARY Introduced rats depredate every life stage of island nesting seabirds, but the extent of predation is rarely quantified. Introduced black rat (Rattus rattus )a nd native deer mouse (Peromyscus maniculatus anacapae) predation on Xantus’s murrelet (Synthliboramphus hypoleucusscrippsi)nestswasexperimentallyquantified usingartificialnestsbeforeandafterrateradicationon AnacapaIsland(California).Thestagedrateradication programmeprovidedexperimentaltreatments:in2002 rats were eradicated on one island (East Anacapa Islet) and remained on two islands (Middle and West Anacapa Islets), providing a control comparison, and, in 2003, rats were eradicated from the remaining islands (Middle and West Anacapa Islets). In 2002, 96% of artificial nests were depredated on control islands (rats present) with rats accounting for most predation. Nest predation on the treatment island (rats eradicated) in 2002 was significantly lower: 8% of artificial nests were depredated, mostly by endemic deer mice. In 2003, following rat eradication on the remaining islands (Middle and West Anacapa Islets), nest predation was reduced from 96% in 2002 to 3% of total nests in 2003. Predation of nests on East Anacapa Islet (rats eradicated in 2002) increased significantly due to reintroduction and recovery of native deer mouse populations, with 23% of artificial nests depredated. The inference is that rat predation on real Xantus’s murrelet nests was responsible for the historically low nesting success and small population sizes of breeding murrelets on Anacapa Island. With rats removed, the hatching success of Xantus’s murrelet chicks and the number of individuals nesting on Anacapa Island will increase dramatically. Artificial nest studies are particularly well suited to quantifying introduced rat impacts on hole and crevice nesting

The potential for biodiversity offsetting to fund invasive species eradications on islands

Abstract Measuring the response of native species to conservation actions is necessary to inform continued improvement of conservation practices. This is particularly true for eradications of invasive vertebrates from islands where up-front costs are high, actions may be controversial, and there is potential for negative impacts to native (“nontarget”) species. We summarize available data on the response of native species on Anacapa Island, California, 10 y after the eradication of invasive black rats Rattus rattus. Native marine taxa hypothesized to respond positively to rat eradication increased in abundance (Scrippss murrelet Synthliboramphus scrippsi; International Union for Conservation of Nature Vulnerable, and intertidal invertebrates). Two seabird species likely extirpated by rats—ashy storm-petrel Oceanodroma homochroa (International Union for Conservation of Nature Endangered) and Cassins auklet Ptychoramphus aleuticus—are now confirmed to breed on the island. Long-term negative effects from n...

Invasive rodent eradication on islands.

N.D. Holmes,∗ ¶ G.R. Howald,∗ A.S. Wegmann,∗ C.J. Donlan,†‡ M. Finkelstein,§ and B. Keitt∗ ∗Island Conservation, 2161 Delaware Ave Suite A, Santa Cruz, CA 95060, U.S.A. †Advanced Conservation Strategies, Via Agusta 12, Cordoba 14011, Spain ‡Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 15853, U.S.A. §University of California at Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, U.S.A.