Rapid eradication of feral pigs (Sus scrofa) from Santa Cruz Island, California

Eradication of invasive alien species from islands is often necessary to protect native biota. The rapidity in which eradication projects are implemented can help reduce risk they will fail. We describe the eradication of feral pigs (Sus scrofa) from Santa Cruz Island, California, highlighting those control techniques that removed the most pigs and those that removed the last pigs. In 411 days, a total of 5036 pigs were removed from the 25,000-ha island. Before the eradication began, the island was fenced into five zones. Within each zone, the same general sequence of control methods was used: trapping (16% of dispatches in 1660 trap-nights); aerial shooting from a helicopter (77% of dispatches in 13,822 km of flight path); and then ground-based hunting with trained dogs (5% of dispatches in 1111 hunter-days). Sterilized adult pigs fitted with radio collars were subsequently used to aid in the location of surviving wild pigs and to monitor the success of the project. Female telemetered pigs were more effective than males at locating remaining wild pigs. Only 10% of the last 102 pigs (the last 20 or so present in each fenced zone) were dispatched as a result of being found with a telemetered pig, but telemetered animals were responsible for finding 43% of the very last pigs once normal hunting had ceased. The time taken to eradicate pigs on Santa Cruz Island was about half that taken on a neighbouring island of similar size (Santa Rosa Island) and 12 times as fast as that on Santiago Island (58,465 ha), Galapagos Islands. The deliberate sequencing of control methods, using first those that taught surviving pigs the least, and the intensive implementation of those methods, represent important advances in the practice of eradication and so biodiversity conservation.     

Reintroduction and establishment of the western barred bandicoot Perameles bougainville (Marsupialia: Peramelidae) at Shark Bay, Western Australia

The western barred bandicoot was reintroduced to the Australian mainland in 1995 after an absence of at least 60 years. The new population was derived from 14 animals, reintroduced to Heirisson Prong from Dorre Island in Shark Bay, Western Australia. Introduced predators (the European red fox and the feral cat) were controlled at the reintroduction site, but European rabbits were not. A large fenced area of natural vegetation within the reintroduction site was used as a secure refuge from mammalian predators. Bandicoots were released from this predator refuge to the 12 km² conservation site. Dispersal from the point of free release was minimal. The reintroduced population has persisted for 4 years and increased, with at least 175 bandicoots recruited to the population in this time. The recapture rate of marked bandicoots was low, suggesting that adult mortality was high. Reproductive output at Heirisson Prong appeared greater than that of the two surviving wild populations on Bernier and Dorre Islands. Litter size was similar, but there was an extended annual breeding season at the reintroduction site. Body condition of reintroduced and wild bandicoots were similar, although there was some indication that reintroduced males may have been in poorer condition than their island counterparts. The litter size of bandicoots increased with a decrease in rabbit abundance, however, bandicoots were able to reproduce, maintain condition, and sustain recruitment to allow the population to increase despite the presence of rabbits. Two fox incursions occurred during the 4-year period of establishment, and feral cats were present on occasion in low numbers. Feral cats may be responsible for a lower rate of population increase than that observed on predator-free Dorre Island. Ongoing predator control is essential for any mainland reintroduction of bandicoots.     

Surplus killing by introduced predators in Australia—evidence for ineffective anti-predator adaptations in native prey species?

Australian examples of surplus killing by mammalian predators were collated. These included surplus killing of native mammals and birds by foxes (Vulpes vulpes) and stock, native mammals and native birds by dingoes (Canis lupus dingo). We found no examples of surplus killing by feral cats (Felis catus). Incidents collated include historical anecdotes of surplus killing by foxes as they colonised the Australian mainland, recent examples where foxes killed threatened native species at sites despite intensive management to exclude foxes, and recent examples of the killing of native species on formerly fox-free islands to which foxes gained entry. Episodes of surplus killings by foxes, other than predation on captive or closely confined animals, appeared different in kind and frequency to those documented for co-evolved predator-prey systems on the large continental landmasses. They did not appear to be uncommon events associated with synchronised births of prey species, unusual or extreme weather that disadvantaged prey species, or seasonal food caching by a predator. Rather, surplus killing events appeared to reflect ineffective anti-predator defences by prey species when encountering a novel and efficient predator to which they have had no evolutionary exposure. We suggest that surplus killing by foxes may have been a feature of, and major contributor to, the rapid mainland extinction or contraction in range of many native species in Australia. In contrast to foxes, examples of surplus killing by dingoes relate mostly to domestic stock (calves and sheep). The arrival of dingoes to the Australian continent preceded that of foxes by 3500-4000 years, but they appear not to have had the dire impact on native mammals that we attribute to foxes. This may be due to fundamental differences in hunting styles and prey size and to their sparse populations in pre-European Australia. Active persecution of non-commensal dingoes by Aborigines, the lack of free-water, and the absence of European rabbits (Oryctolagus cuniculus) as an alternative food supply would have limited their numbers and their impact on native mammals.     

The impact of feral cats and dogs on populations of the West Indian rock iguana, Cyclura carinata

A population of rock iguanas, Cyclura carinata, inhabiting Pine Cay in the Caicos Islands was nearly extirpated during the three years following construction of a hotel and tourist facility. The decline, from an estimated adult lizard population of nearly 5500, was due primarily to predation by domestic dogs and cats introduced to the island simultaneously with hotel construction. Population declines on other nearby islands were also attributed to predation by these feral mammals.     

Swift fox reintroductions on the Blackfeet Indian Reservation, Montana, USA

Swift foxes (Vulpes velox) were once common prairie inhabitants throughout western North America and were integral components within ecosystems and some Native American tribal cultures. In response to extirpation from tribal lands, the Blackfeet Tribe and Defenders of Wildlife reintroduced 123 captive-raised swift foxes from 1998 to 2002 to the Blackfeet Indian Reservation, Montana, USA. We used two success criteria, a population growth rate ?1.0 and an index count ?100 foxes, to determine if the reintroduction was a short-term success.We radiocollared and monitored swift foxes from 2003 to 2005 to estimate survival and fecundity. The swift fox population grew at a rate of 16% during 2003/2004 and 14% in 2004/2005. In addition, field crews observed 93 foxes in the summer of 2005.The swift fox population reached one, and very nearly both, of our short-term success criteria. In light of swift fox sign in areas where we were unable to observe foxes despite being aware of their presence, we believe there were ?100 foxes present in 2005. Based on our success criteria and the discovery of swift foxes 110 km from the release site, we consider this reintroduction a short-term success with promise for long-term success. The Blackfeet Tribe and Defenders of Wildlife have attained their goal of restoring a culturally important species to Tribal lands and have initiated a comeback of swift foxes beyond the Reservation border to the Rocky Mountain Front in Montana. Collaborative projects between tribes and non-governmental groups can play a vital role in our effort to conserve biologically and culturally significant species.     

Ecology and use of arctic fox Alopex lagopus dens in Norway: tradition overtaken by interspecific competition?

Arctic fox Alopex lagopus dens in Norway are mostly large and well-defined structures of great age. Examinations of these dens have been used in surveys of the breeding and population status of the arctic fox in Fennoscandia. In this study, dens all over north Norway and in some parts of south Norway were surveyed (n=214), and several aspects of den characteristics, localisation and use were recorded. Red fox Vulpes vulpes dens were also recorded whenever found, including red fox use of arctic fox dens (total n=211). Most of the arctic fox dens were of the “classic” type dug out in sandy soil (n=210). The average number (±1 SD) of open entrances (at least half open) was 27.4±19.0, and the average size was 363.1±288.7 m². Regional variation was found in both these measurements, as well as in two variables classifying the vegetation at the den. However, no consistent south-north gradient was found, although the most southern and the most northern regions were extremes in several respects. A positive correlation was found between den size and the number of entrances, as well as between these two variables and the two vegetation variables. For each arctic fox den, height above the tree line, distance to the tree line, distance between arctic fox dens, distance to the nearest red fox den, distance to a main road and distance to other human activity were estimated. Regional variation was found in all these variables, but no consistent south-north gradient. Again, the most southern region deviated most. There were large differences in the proportion of dens used by arctic foxes between the nine regions, with one region outstanding in its production of arctic fox litters and paucity of red foxes. The proportion sum of arctic fox entrances to sum of red fox entrances reliably, but not perfectly, identified the best arctic fox regions. Arctic fox dens that were known to have produced litters at least once during 1980-2001 had about twice as many entrances as dens without pups, were 32% larger and had a more lush vegetation. They were also situated further from a red fox den. Distance to red fox dens and height above the tree line were the most important factors regarding arctic fox use of dens. Thus, the red fox was identified as a threat to the arctic fox population.     

Island differences in population size structure and catch per unit effort and their conservation implications for Komodo dragons

Species inhabiting archipelagos are often characterised by high levels of interpopulation divergence (e.g. size related traits). This divergence may, in turn, influence their life-history. To facilitate better management and conservation of the Komodo dragon (Varanus komodoensis), an island endemic, we identified demographic differences between two island populations in Komodo National Park, Indonesia. Comparison of data collected from dragon populations inhabiting Rinca Island and the much smaller Gili Motang Island indicated that between 1994 and 2004, the Komodo dragon population on Gili Motang significantly decreased its: (1) mean body mass, (2) body condition and (3) relative abundance. These results suggest that the numerically small Gili Motang population was oscillating downwards; in contrast, the Rinca Island population had been relatively stable. More importantly these results emphasize the necessity for managers of this priority conservation species to understand further the inherent functional differences among dragon populations to develop island specific management units. Current management practices (e.g. monitoring) instigated by Komodo National Park management ignore small island dragon populations and thus run the risk of being unable to detect adverse effects for populations that are potentially most prone to decline.     

The Prince Edward Islands: A sanctuary for seabirds in the Southern Ocean

This paper reviews the breeding distribution and numerical status of selected species of seabirds at 23 oceanic island groups in the Southern Ocean (between latitudes 35 and 70°S), based on census data and population estimates which have become available through increased scientific endeavour in the region during the last 15 years or so. The paper focuses on the avifauna of the Prince Edward islands, in the southern Indian Ocean, and points to the importance of these islands as a breeding station and sanctuary for seabirds. Only one oceanic island group, the Crozets, contains more species of breeding seabirds than the Prince Edward islands. Substantial segements (about 10% and greater) of the world breeding populations of the king and macaroni penguins, and the wandering, grey-headed, yellow-nosed and sooty albatrosses are based at the Prince Edward group. We recommend that Prince Edward Island (sensu stricto) should be a wilderness area, and that development at Marion Island should be kept to an absolute minimum.     

Current status of rodents on islands in the Gulf of California

On islands in the Gulf of California, many species and subspecies of rodents are relict species, restricted to the islands, and now considered extinct or verging on extinction. From 1991 to 1999, each island was surveyed and an average of 15 work-nights were spent on each island, for a total of 15,000 trap-nights. A Fourier series was used to estimate population density. Five native taxa are now considered extinct (Chaetodipus baileyi fornicatus, Peromyscus guardia mejiae, P. g. harbinsoni, P. pembertoni, and Neotoma bunkeri). Two species are at risk of extinction (Dipodomys insularis and Neotoma albigula varia). The most probable cause for extinction is the introduction of nonnative species, specifically cats. We believe that the most vulnerable rodent populations of the islands in the Gulf of California to non-native species are Neotoma lepida latirostra on Danzante island and Neotoma lepida abbreviata on San Francisco island, both in the state of Baja California Sur.     

Soil response to canopy position and feral pig disturbance beneath Quercus agrifolia on Santa Cruz Island,California

We assessed the effects of canopy position and feral pig disturbance on soil moisture, pH, and inorganic nitrogen concentrations beneath canopies of Quercus agrifolia and surrounding grasslands on Santa Cruz Island, California. Percent soil moisture, pH, nitrate-N, and total inorganic nitrogen varied significantly with canopy position. Soil moisture decreased, and pH increased along transects from the subcanopy trunk position to the open grassland outside the canopy. Nitrate and total nitrogen increased from the trunk position to midcanopy and then decreased from midcanopy to the open grassland position. The ratio of nitrate to ammonium varied with canopy position, even after controlling for the effects of soil moisture and pH, both of which strongly influence rates of nitrogen mineralization. Temporally, soil pH, soil moisture, nitrate-N, and total carbon all varied significantly between drought and non-drought years. Soils from fenced exclosures that removed feral pig disturbance did not exhibit significant differences in any soil property compared to control plots where pig access was permitted. The results of our analysis suggest that the primary factors influencing spatial and temporal variability in oak woodland soils on Santa Cruz Island were subcanopy position and climate variability, respectively. Biotic disturbance by feral pigs did not cause a significant cause in soil properties over the spatial and temporal domains examined in this study.     

Assessing the risks of introduced chickens and their pathogens to native birds in the Galápagos Archipelago

Poultry production is an important economic activity on inhabited islands of the Galápagos archipelago. There has been a recent surge in both small-scale backyard chickens and larger scale broiler production associated with growth in the human population and the tourist industry. With increased poultry production, concerns have been expressed about the increasing risk of transfer of disease from chickens to native Galápagos bird species that may have little resistance to introduced pathogens [Wikelski, M., Foufopoulos, J., Vargas, H., Snell, H., 2004. Galápagos birds and diseases: invasive pathogens as threats for island species. Ecology and Society 9(5). Available from: URL:http://www.ecologyandsociety.org/vol9/iss1/art5]. This study evaluates risks posed by chicken disease to endemic and native Galápagos bird species, based on empirical evidence of pathogens present in chickens on the islands and a literature review of effects of these pathogens in wild species. Pathogens identified in domestic chicken populations of immediate avian conservation concern are Newcastle disease, Mycoplasma gallisepticum, and the proventricular parasite Dispharynx sp. Newcastle disease (avian paramyxovirus-1) poses an imminent threat to Galápagos penguins (Spheniscus mendiculus), flightless cormorants (Phalacrocorax harrisi), and lava gulls (Larus fuliginosus), species with very small population sizes (less than 1500 animals each). Additionally, litter from broiler farms could affect ecological processes in local ecosystems. Improved poultry biosecurity measures are urgently needed on the Galápagos Islands for avian disease management, yet developing these strategies presents political, social, and economic challenges.     

High levels of hatching failure in an insular population of the South Island robin: a consequence of food limitation?

Endangered birds in insular environments like New Zealand are often translocated to predator-free offshore islands for conservation purposes. Some translocated populations however exhibit reduced fecundity, and it has been suggested that either inbreeding (due to small number of founders) or resource shortages (due to high population density) may limit reproductive success. For example, the South Island robin (Petroica a. australis) population on Motuara Island (59 ha) was founded by only five birds but has increased to ∼600 individuals, or a density >10 times that of the mainland. Despite this apparent success, the rate of hatching failure in this population is three times higher than in mainland populations, with more than a third of eggs failing to hatch. To test if elevated hatching failure is the result of food limitation, we carried out a food supplementation experiment by providing females with mealworms equivalent to ∼50% of their daily energy requirements. Food supplementation had no effect on hatching success, clutch size, incubation attentiveness or nest size. Egg volume increased with food supplementation in one of the two years of this study, but both egg volume and incubation attentiveness were unrelated to rate of hatching failure. As previous genetic analyses confirmed that the bottlenecked population of robins on Motuara Island have significantly less genetic variation than their source population, we conclude that inbreeding depression, and not food limitation, is the most likely explanation for their high rate of hatching failure. We suggest that the experimental translocation of genetically dissimilar individuals be considered as a possible remedy for low productivity in island populations that were initiated with few founders.     

Rabbit and fox introductions in tierra del fuego: history and assessment of the attempts at biological control of the rabbit infestation

Four European rabbits Oryctolagus cuniculus were introduced in the Chilean side of Tierra del Fuego island in 1936. At the height of the rabbit infestation (1953) they numbered about 30 million. Twenty-four foxes Dusicyon griseus were released in Tierra del Fuego in 1951, three years before the myxoma virus decimated the rabbit populations. We document the history of the introductions of both rabbits and foxes in Tierra del Fuego, and evaluate the role of foxes as biological-control agents for the rabbits.     

Evaluating potential infectious disease threats for southern resident killer whales, Orcinus orca: a model for endangered species

Infectious diseases have the potential to play a role in the decline of threatened wildlife populations, as well as negatively affect their long-term viability, but determining which infectious agents present risks can be difficult. The southern resident killer whale, Orcinus orca, population is endangered and little is known about infectious diseases in this species. Using available reference literature, we identified 15 infectious agents (bacteria, viruses, and fungi) reported in free-ranging and captive killer whales, as well as 28 additional infectious agents reported in free-ranging and captive odontocete species sympatric to southern resident killer whales. Infectious agents were scored as having a high, medium, or low ability to affect fecundity or reproductive success, to cause disease in individual animals, and to cause epizootics. Marine Brucella spp., cetacean poxvirus, cetacean morbilliviruses, and herpesviruses were identified as high priority pathogens that warrant further study. Using identified pathogens to develop a standardized necropsy and disease testing protocol for southern resident killer whales and sympatric odontocetes will improve future efforts to better understand the impacts of priority and non-priority infectious agents on southern resident killer whales. This model can be used to evaluate potential infectious disease risks in other threatened wildlife populations.     

Current status of two endangered Caribbean rodents

Living rodents of the genus Geocapromys of the hutia family have been known during this century on three Caribbean islands (Walker, 1968). Visits were made in 1974 to Jamaica and Little Swan Island to check the current status of two of these endangered populations. It appears from these field investigations that the Swan Island hutia, Geocapromys brownii thoracatus, has been exterminated from Little Swan Island. The main cause may have been predation by cats introduced in the late 1950s and after. The Jamaican hutia, G. b. brownii, remains in three remote areas of Jamaica. It exists at low population levels which have been much reduced from those occurring 30 years ago. The Jamaican hutias are shy and secretive in habits compared to the undisturbed Bahamian hutias, G. i. ingrahami, of East Plana Cay, Bahama Islands.     

Using ecological niche modelling to infer past, present and future environmental suitability for Leiopelma hochstetteri, an endangered New Zealand native frog

Leiopelma hochstetteri is an endangered New Zealand frog now confined to isolated populations scattered across the North Island. A better understanding of its past, current and predicted future environmental suitability will contribute to its conservation which is in jeopardy due to human activities, feral predators, disease and climate change. Here we use ecological niche modelling with all known occurrence data (N = 1708) and six determinant environmental variables to elucidate current, pre-human and future environmental suitability of this species. Comparison among independent runs, subfossil records and a clamping method allow validation of models. Many areas identified as currently suitable do not host any known populations. This apparent discrepancy could be explained by several non exclusive hypotheses: the areas have not been adequately surveyed and undiscovered populations still remain, the model is over simplistic; the species’ sensitivity to fragmentation and small population size; biotic interactions; historical events. An additional outcome is that apparently suitable, but frog-less areas could be targeted for future translocations. Surprisingly, pre-human conditions do not differ markedly highlighting the possibility that the range of the species was broadly fragmented before human arrival. Nevertheless, some populations, particularly on the west of the North Island may have disappeared as a result of human mediated habitat modification. Future conditions are marked with higher temperatures, which are predicted to be favourable to the species. However, such virtual gain in suitable range will probably not benefit the species given the highly fragmented nature of existing habitat and the low dispersal ability of this species.     

Conservation action in the Galàpagos: feral pig (Sus scrofa) eradication from Santiago Island

Introduced mammals are major drivers of extinction and ecosystem change. As omnivores, feral pigs (Sus scrofa) are responsible for wholesale adverse effects on islands. Here, we report on the eradication of feral pigs from Santiago Island in the Galápagos Archipelago, Ecuador, which is the largest insular pig removal to date. Using a combination of ground hunting and poisoning, over 18,000 pigs were removed during this 30-year eradication campaign. A sustained effort, an effective poisoning campaign concurrent with the hunting program, access to animals by cutting more trails, and an intensive monitoring program all proved critical to the successful eradication. While low and fluctuating control efforts may help protect select native species, current eradication methods, limited conservation funds, and the potential negative non-target impacts of sustained control efforts all favor an intense eradication effort, rather than a sustained control program. The successful removal of pigs from Santiago Island sets a new precedent, nearly doubling the current size of a successful eradication, and is leading to more ambitious projects. However, now we must turn toward increasing eradication efficiency. Given limited conservation funds, we can no longer afford to spend decades removing introduced mammals from islands.     

The ecology and conservation of reptiles on Round Island and Gunner's Quion,Mauritius

The reptile communities on two islands off the north coast of Mauritius are described. One of these islands, Round Island, is the last refuge for four species: Phelsuma guentheri, Leiolopisma telfairii, Bolyeria multocarinata and Casarea dussumieri, which together with four more species form a relict herpetofauna of great scientific and conservation interest. The reptile fauna of the neighbouring island of Gunner's Quoin has been reduced to four species, probably because of habitat destruction and the effects of ship rats Rattus rattus. Round Island has also suffered habitat destruction through introduced mammals but because of its remoteness, rats are absent. Conservation of the Round Island ecosystem is discussed; removal of the remaining alien herbivores, the rabbit Oryctolagus cuniculus and conservation education about Round Island are the main recommendations.     

Ecology and conservation of two endangered subspecies of the leopard cat (Prionailurus bengalensis) on Japanese islands

The conservation of rare species on islands is a special challenge, especially when the islands are faced with increasing human impact. Two endangered wild felids in Japan provide a contrast that is useful for examining conservation strategies. The Iriomote cat (Prionailurus bengalensis iriomotensis) is endemic to Iriomotejima Island in Okinawa, and the Tsushima leopard cat (Prionailurus bengalensis euptilurus) occurs in the Tsushima islands in Japan, although a related subspecies found in the Korean Peninsula. Population size was approximately 100 individuals for each subspecies. While the population of Iriomote cat appears relatively stable, the population and abundance of the Tsushima leopard cat has decreased in recent decades. Because of their small population sizes and restricted habitats both are listed as endangered species/subspecies in Japan’s Red List, and the Iriomote cat is listed as an endangered subspecies in the IUCN Red List. Although both are similar-sized felids living on small islands, their ecological characteristics such as food habit, habitat selection, and density differ. These differences seem to be caused by the climate, the biological environment (the species composition of fauna in each island, and the presence of competitors), and the artificial background. The threats facing these two felids are also similar. Habitat destruction, traffic accidents, and negative influences by introduced species are the principal threats to be addressed for their conservation. At the same time, there are differences in the degree of impact by each threat, in each species’ conservation programs in practice, and in the stages of progress and operation of programs. These differences are partly because they have different ecological features and partly because the social background of each island, such as human population, main industry, and historical relationship between human and wildlife, are quite different. We will compare the ecology and state of these two wild felids and discuss the different conservational situations in relation to felid ecology and human society.     

Insular pest control within a metapopulation context

Introduced pests threaten many species and their control is generally beneficial for conservation, particularly on islands where complete eradication is possible. Unfortunately on ‘nearshore’ islands neighbouring source populations exist and unaided reinvasion is likely. Pest control programmes at these sites thus require a metapopulation context to adequately manage movements between source and sink populations. We investigated the ecology of introduced ship rats (Rattus rattus) on a nearshore island, and gene flow with adjacent mainland populations, in order to understand the metapopulation dynamics and relative levels of pest control required within the landscape. We sampled the entire population by trapping (n = 30), achieving eradication, and found a low rat density (3.2 ha⁻¹) indicative of a sink population. Seed and other plant material constituted the major dietary component of rats. Despite its proximity to mainland source populations, the island population was genetically distinct with reduced allelic diversity caused by a recent reinvasion founder effect. Genetic analyses also detected recent migrants between the populations. In contrast, two mainland populations separated by a similar distance displayed complete genetic mixing. The small water gap therefore provides a sufficient barrier to lower the migration rate to the island and delay reinvasion, which nonetheless eventually happens. In order to maintain nearshore islands pest-free, conservation management will require a metapopulation approach simultaneously focusing on both island and source population pest control.