Eradication of Norway Rats for Recovery of Seabird Habitat on Langara Island, British Columbia

Introduced Rattus norvegicus (Norway rats) caused the decline of Synthliboramphus antiquus (ancient murrelets) and other seabirds breeding on Langara Island (approximately 3,100 ha), British Columbia. Using funds from the litigation settlement following the Nestucca oil spill, Environment Canada eradicated Norway rats using a technique developed in New Zealand which involved dispensing wax baits containing the anticoagulant brodifacoum at 50 ppm from fixed bait stations. Bait stations were placed every 75 to 100 m on a grid over the entire island (1 station/ha). Rats removed bait for 26 days, after which crews placed baits in protective plastic bags in each bait station. Stations loaded with baits were left on the island and rechecked four times over 2 years, after which bait stations and remaining bait were removed. The eradication succeeded. No signs of rats have been detected on Langara Island and its associated islands since January 1996. No rats were trapped during 1,700 trap‐nights following the poison campaign. Incisor marks of rats were not found on apples or oil‐dipped chew‐sticks. Corvus corax (common ravens) likely suffered greater than 50% mortality from the eradication after apparently gaining access to the poison directly from bait stations and from scavenging rat carcasses. A monitoring and response system is being developed in conjunction with current users of the islands. The success on Langara Island demonstrates how the technique proven on small New Zealand islands of less than 300 ha can be effectively extrapolated to much larger islands.     

The use of poison eggs for the control of stoats

Abstract

Stoats (Mustela erminea) are an important predator of many forest bird species in New Zealand, and more effective methods for their control are being sought. Stoat control using Fenn traps has been shown to prevent predation on mohua (Mohoua ochrocephala), but this technique is labour‐intensive and costly to use for protection of large areas of habitat. We evaluated 1080 delivered in eggs as a poison for control of stoats. The lethal dose has been determined by captive and field trials, but attempts to implement a large‐scale control operation have given inconclusive results. To clarify the effectiveness of 1080 eggs as a control technique, we carried out further field trials with radio‐tagged stoats in the Makarora Valley. Twenty animals were monitored by radio tracking, and data loggers and video cameras recorded their visits to bait stations. The precise time an individual stoat ate a poison egg could be determined from data logger and video information, and its fate was followed. Sixteen of twenty stoats were killed by 1080 eggs, three died of other causes and one remained alive at the end of the trials.     

Palatability and efficacy to possums and rats of pest control baits containing bird repellents

Repellents used to reduce by-kill of birds during pest control must not compromise acceptance by target species. Two repellents combined, anthraquinone (AQ; 0.4 g kg^?1) and d-pulegone (DP; 1.0) did not reduce the palatability of blue-coloured carrot baits to laboratory rats (Rattus norvegicus); nor did DP (2.0). Green-coloured carrot baits coated with AQ, DP or AQ + DP were taken from bait stations by wild possums (Trichosurus vulpecula) and rats. Toxic (1080) bait coated with AQ (0.4) and peanut oil (0.1) had reduced palatability but was accepted by laboratory rats. However, laboratory rats did not consume enough baits coated with AQ and bacon, peanut butter, cinnamon or DP to be killed. Anthraquinone (0.4 or 0.8) plus cinnamon and DP (0.5) did not affect palatability or lethality to captive ship rats (R. rattus) or possums. Anthraquinone and DP as surface coatings on baits are therefore acceptable to possums and possibly rats, at concentrations that deter some bird species.     

A monitoring program for Patagonian foxes based on power analysis

Culpeo fox (Pseudalopex culpaeus) and gray fox (Pseudalopex griseus) are heavily culled in Patagonia. Fox populations seem to persist thanks to spatial refuges from which hunted areas are repopulated, following a source–sink dynamics. Sustainable use of Patagonian foxes warrants the design of a monitoring program in nature reserves and areas subjected to predator control. During 7 years, we used visitation indices to bait stations in a national park and neighboring sheep ranches of southern Argentina. We operated bait stations during three consecutive nights and calculated seven indices of relative abundance. For each fox species, we compared the power of different monitoring designs and scenarios that combined visitation indices, effort (number of bait station lines and survey frequency) while controlling for type I error, and magnitude of population change during a given period. We looked at the combinations that produced high power (β ≤ 0.24). The operation of bait stations during several nights markedly increased statistical power. Index 7 (recording visits 72 h after activation) exhibited the lowest variation and improved expected power to detect a population trend. Both fox species could be monitored simultaneously, with power >0.76 in the short term (5 years), activating 24 bait station lines. We conclude that monitoring programs for culpeo fox and gray fox based on bait stations are able to detect marked declines but are less useful to reliably detect moderate increases in abundance, especially in sheep ranches.

     

Lethal 1080 baiting continues to reduce European Red Fox (Vulpes vulpes) abundance after more than 25 years of continuous use in south‐west Western Australia

European Red Fox (Vulpes vulpes) baiting with 1080 poison (sodium fluoroacetate) is undertaken in many Australian sites to reduce fox abundance and to protect vulnerable native species from predation. The longest continuous use of fox baiting for fauna conservation commenced in south‐west Western Australia in the 1980s and includes baiting Dryandra Woodland and Tutanning Nature Reserve. The trap success of the Woylie (Bettongia penicillata) in these two reserves initially increased more than 20‐fold after the commencement of baiting and was maintained until 2000. Woylie captures then decreased rapidly, despite ongoing fox baiting, so the long‐term efficacy of 1080 baiting was questioned. Here, fox density and probabilities of detection, re‐detection and survival between replicated baited and unbaited sites were compared by modelling capture–recapture of individual foxes. These were identified from microsatellite DNA genotypes obtained non‐invasively from hair, scat and saliva samples. The frequency and duration of fox residencies were also quantified. Remote cameras were used to determine the fate of baits but uptake by foxes was low, whereas nontarget species' bait uptake was high. Nevertheless, foxes inhabiting baited reserves had significantly higher mortality, shorter residency times, and 80% lower density than foxes inhabiting unbaited reserves. Baiting continues to significantly reduce fox abundance after more than 25 years of continuous use. This has positive implications for fox control programmes throughout Australia but reduced fox abundance may facilitate increased predation by feral Cats (Felis catus).     

Bait shyness and its prevention in the rabbit Oryctolagus cuniculus L.

Abstract

Caged New Zealand white rabbits were examined for the development, and prevention, of a learned aversion to toxic feed. Two familiar feeds were offered. One feed, a paste, contained sublethal amounts of sodium monofluoroacetate (1080); the other feed, cereal‐based pellets, was unpoisoned. On initial poisoning, consumption of both feeds decreased, but more markedly for the 1080‐dosed pastes. Suppressed feed consumption was observed for several days and may have been illness induced. A second poisoning elicited a significant depression of consumption of pastes but not pellets. The addition of a mixture of certain drugs (neurotransmitter antagonists) to the poisoned paste appeared to prevent the characteristic depression of this paste intake. We speculate that the drugs disrupted the associative process linking 1080 to recognisable attributes of the toxin or bait itself.

The implications of these results on aversion formation in rabbits and pest control are discussed.     

Controlling small mammal predators using sodium monofluoroacetate (1080) in bait stations along forestry roads in a New Zealand beech forest

A single five night pulse of sodium monofluroacetate (0.15% 1080) applied in bait stations at two different spacing intervals, 100 and 200 m, along forestry roads in New Zealand beech forest, killed all four of the resident radio-tagged stoats (Mustela erminea) and all three of the resident radio- tagged wild house cats (Felis catus) by secondary poisoning. Gut contents of predators indicated that house mice (Mus musculus), ship rats (Rattus rattus) and bushtail possums (Trichosurus vulpecula) were important sources of the toxin. High kills of predators, possums and rats at both 100 and 200 m spacing regimes suggest that greater efficacy of controlling these pests would be achieved with the latter method. Evidence suggests that routine management of possums and rats using 1080 and brodifacoum has resulted in widespread control of small mammalian carnivores by secondary poisoning in New Zealand forests. However, aerial application of poison can kill large numbers of tomtits (Petroica macrocephala) and robins (Petroica australis) and few other native bird species have been adequately monitored through such operations. Reducing risks to native wildlife is responsible ecological management. Use of bait stations along forestry roads or tracks may be fundamental in mounting cost-effective :Large-scale ground-based protection of native wildlife through safer predator controls.     

Heavy rimu (Dacrydium cupressinum) mast seeding and rat (Rattus spp.) population eruptions on Stewart Island/Rakiura

Abstract

This study aimed to quantify changes in rat abundance and population structure before, during, and after a rimu (Dacrydium cupressinum) mast seed event in lowland forest on Stewart Island, New Zealand. Rats, primarily ship rats (Rattus rattus), were trapped in low numbers throughout the study period (March 2000‐March 2003), except when they erupted to very high abundance in spring 2002, shortly after heavy rimu seed fall. In the immediate post‐peak phase, scavenging of trapped rats increased substantially; rats were seen and trapped in daylight; and weights of adult female rats were low in relation to their size, which suggests that food shortage was the cause of the subsequent steep decline in abundance. Rat eruptions have been observed on Stewart Island after heavy rimu seed fall several times over the past 40 years. Eruptions of rats caused by heavy rimu seed‐fall may have triggered the invasion of nearby islands by rats, and caused the extinction of several native species on Stewart Island.     

Large-Scale Poisoning of Ship Rats (

This paper describes the impact of nine poison operations on ship rats in four areas (35 ha to 3200 ha) of North Island forest. Poisoning with 1080, brodifacoum, or pindone killed 87- 100% of rats, based on trapping and tracking-tunnel indices. Rat populations took 4-5 months to recover. Operations to protect nesting birds should therefore coincide with the onset of nesting and be rePeated each year, although not necessarily with the same methods. Population reduction declined each year at Mapara, King Country, during three annual 1080 operations which used the same lures and baits, but remained high at Kaharoa, Bay of Plenty, where poison toxicity was higher, non- toxic bait was pre-fed, and poisoning methods varied each year. Mouse tracking rates increased in poisoned forests 3-6 months after poisoning if the initial kill of rats exceeded 90%, Peaked 7-9 months after poisoning, then declined to pre-poison levels. Future research should focus on how prey and non-prey species within a forest community respond to a temporary reduction in rat numbers, and on methods to maintain low rat densities after initial knock-down.     

Experimental suppression of ants foraging on rainforest vegetation in New Guinea: testing methods for a whole‐forest manipulation of insect communities

1. Ants are extremely abundant in lowland tropical forests where they are important predators, plant mutualists, and herbivores. Their complex role in tropical plant–insect food webs can be best assessed by experimental manipulation of their abundance. Historically, ant exclusion experiments have had a small‐scale focus, such as single trees. Here, we test a new ‘whole‐forest' method of ant exclusion, using treated canopy bait stations, in a diverse tropical rainforest in New Guinea. 2. We conducted a 10‐month manipulative experiment in primary and secondary rainforests. In each forest type, a 625 m² treatment plot was isolated from the surrounding forest and 135 bait stations treated with fipronil, S‐methoprene, and hydramethylnon were placed in trees to suppress ants. Ant activity was monitored in the forest canopy and understorey with an additional 65 stations in treatment and control plots. 3. We achieved a dramatic decline in ant abundance in treatment plots compared with controls in both forest types, with an average decrease in ant numbers per station of 82.4% in primary and 91.2% in secondary forest. In particular, native dominant species Oecophylla smaragdina, Anonychomyrma cf. scrutator in primary forest, and invasive Anoplolepis gracilipes in secondary forest were greatly affected. In contrast, Tapinoma melanocephalum flourished in treatment plots, perhaps benefiting from reduced competition from other ant species. 4. Our study demonstrates that it is possible to selectively eradicate most of the foraging ants in a structurally complex tropical forest. We propose whole‐forest manipulation as a novel tool for studying the role of ants in shaping plant–insect food webs.     

From small Maria to massive Campbell: Forty years of rat eradications from New Zealand islands

Abstract

Over the last four decades the eradication of rats from islands around New Zealand has moved from accidental eradication following the exploratory use of baits for rat control to carefully planned complex eradications of rats and cats (Felis catus) on large islands. Introduced rodents have now been eradicated from more than 90 islands. Of these successful campaigns, those on Breaksea Island, the Mercury Islands, Kapiti Island, and Tuhua Island are used here as case studies because they represent milestones for techniques used or results achieved. Successful methods used on islands range from bait stations and silos serviced on foot to aerial spread by helicopters using satellite navigation systems. The development of these methods has benefited from adaptive management. By applying lessons learned from previous operations the size, complexity, and cost effectiveness of the campaigns has gradually increased. The islands now permanently cleared of introduced rodents are being used for restoration of island‐seabird systems and recovery of threatened species such as large flightless invertebrates, lizards, tuatara, forest birds, and some species of plants. The most ambitious campaigns have been on remote subantarctic Campbell Island (11 300 ha) and warm temperate Raoul Island (2938 ha), aimed to provide long‐term benefits for endemic plant and animal species including land and seabirds. Other islands that could benefit from rat removal are close inshore and within the natural dispersal range of rats and stoats (Mustela erminea). Priorities for future development therefore include more effective methods for detecting rodent invasions, especially ship rats (Rattus rattus) and mice (Mus musculus), broader community involvement in invasion prevention, and improved understanding of reinvasion risk management.     

Residues of brodifacoum and other anticoagulant pesticides in target and non‐target species,Nelson Lakes National Park,New Zealand

Abstract

Cereal‐based bait containing 20 ppm brodifacoum was used in bait stations continuously from December 1997 to August 2000 in the Rotoiti Nature Recovery Project area, for controlling brushtail possum (Trichosurus vulpecula), ship rat (Rattus rattus), and house mouse (Mus musculus) populations. Concurrently (and before and after), baits containing brodifacoum, bromadiolone, flocoumafen, coumatetralyl, or warfarin were also used in St Arnaud village and on farms immediately adjacent to the project area. Brodifacoum residues were detected in the livers of 234 mammals from eight species, and two birds from two species captured alive, and a further seven birds from five species found dead in the project area (cause of death unknown). The highest concentration of brodifacoum residues in mammalian livers was recorded during the period brodifacoum was used in the project area. However, residues were present in the livers of some individuals at least 24 months after brodifacoum use in the project area stopped. These residues may have persisted in animals surviving brodifacoum use in the project area, and/or been transported into the area by animals moving to and from the adjacent village and farms, where brodifacoum use continued. Residues of flocoumafen, coumatetralyl, or warfarin, used only in the village and on farms, were also detected in the livers of animals captured up to at least 8 km from the nearest source. The results concur with other studies cautioning against indiscriminate or prolonged use of persistent anticoagulants for vertebrate pest control. However, the risks from such pesticides must be balanced against the demonstrable benefits of reducing pest abundance.     

Animal v. plant‐based bait: does the bait type affect census of fish assemblages and trophic groups by baited remote underwater video (BRUV) systems?

Coral reef fish communities were sampled at the Nayband Marine Park, Iran, using baited remote underwater video stations (BRUVSs) which incorporated animal (i.e. frigate tuna Auxis thazard and beef liver), or plant‐based baits (i.e. raw dough and raw dough‐turmeric powder mix). The A. thazard was found to record significantly (P < 0·05) higher species richness and number of carnivorous fishes than plant‐based baits, while abundance of herbivores was maximum in raw dough‐turmeric powder mix trials. There was also a significant difference in trophic composition of fish assemblages surveyed by animal‐ and plant‐based baits which seemed to be due to variations in attraction patterns of carnivores and herbivores occurring at the earlier phases of each BRUV deployments. Meanwhile, the assemblage structure was comparable among fish assemblages sampled by different bait treatments, indicating that species‐level responses to each bait type may be more complicated. In essence, the efficiency of mixed baits should also be examined in future studies.     

Attract‐and‐kill systems efficiency against Ceratitis capitata (Diptera: Tephritidae) and effects on non‐target insects in peach orchards

For control of the Mediterranean fruit fly Ceratitis capitata (Diptera: Tephritidae), the attract‐and‐kill or attracticide technique is an alternative to the spraying of traditional organophosphate pesticides. In this study, the effectiveness of Ceranock and AAL&K attract‐and‐kill bait stations was assessed for control of C. capitata in Tunisian peach (Prunus persica) orchards. Our results showed that, in orchards with early‐ripening varieties, the numbers of C. capitata males and fruit damage were significantly lower in plots treated with Ceranock and AAL&K bait stations than in plots treated with conventional organophosphate and pyrethroid insecticides. In addition, the abundances of non‐target insects in the Chrysopidae, Coccinellidae and Miridae were significantly greater in plots treated with the bait stations than in plots treated with the conventional pesticides; that is, the use of attract‐and‐kill bait stations had fewer negative effects than the application of conventional pesticides on the biological diversity in Tunisian peach orchards. Overall, the results indicate that Ceranock and AAL&K attract‐and‐kill bait stations are useful alternatives for the control of C. capitata in Tunisian peach orchards planted with early‐ripening varieties.     

A review of potential techniques for identifying individual stoats (Mustela erminea) visiting control or monitoring stations

Abstract

We review ways of individually identifying stoats (Mustela erminea) and similar small mammals from visits to bait stations or to monitoring devices in the field. Tracking devices are the cheapest and most practical method currently available of measuring the presence of a particular species, but there has been little research on the recognition of individuals. Elongation of tracking tunnels, or using sooty plates rather than ink to record prints, may improve detectability of individual markings. Recording visits to bait stations or tracking tunnels from DNA sequencing of hair or skin samples is likely to be prohibitively expensive for many monitoring programmes. Identification of stoats visiting bait stations or tracking tunnels using electronic devices has great potential, but these techniques are impracticably expensive because stoats move over such large areas that individual receivers and data loggers would be needed for each bait station. Chemical bait markers such as rhodamine B may be the most suitable method for identifying which animals have used a particular bait station.     

Bait Stations for Detection and Control of Alien Rats in Galapagos

ABSTRACT Alien rats have impacted native systems worldwide, yet wildlife managers lack techniques to efficiently monitor for rodent invasions where native rodents are present and to control alien rodents sympatric with native rodents. We tested the ability of vertical bait stations to exclude native rodents in the Galapagos Islands, Ecuador. Norway rats (Rattus norvegicus) appeared able to enter all station sizes, whereas black rats (R. rattus) were excluded from larger stations. The endemic rodents Oryzomys bauri and Nesoryzomys narboroughi were unable to enter bait stations of any size, but N. swarthi entered the smallest station. Differences in climbing technique contributed to the advantage of alien rodents over endemic species. Our technique provides wildlife managers in the Galapagos, and potentially other islands with native rodents, a means for early detection and control of alien rats.     

Field trials of slow‐release synthetic lures for stoats (Mustela erminea) and ferrets (M. furo)

Abstract

Experimental field trials were used to compare the attractiveness to stoats (Mustela erminea) and ferrets (M. furo) of traps set with either a synthetic scent lure or with fresh food bait. One lure, containing 2‐n‐propylthietane, effectively attracted as many ferrets as did rabbit meat bait. Fewer stoats were caught with this lure than with egg bait. Made up in a slow‐release formulation in “plastic rope”, the lure remained attractive to ferrets for at least 2 weeks under sunny field conditions. Traps containing a second lure, 3‐n‐propyl‐l,2‐dithiolane, were less successful at catching both mustelid species than those containing fresh food baits. The scent lures were not attractive to non‐target species, but neither did they deter some species.     

Hoarding behavior by ship rats (Rattus rattus) in captivity and its relevance to the effectiveness of pest control operations

Hoarding of food items is well known among muroid rodents, but evidence for hoarding behavior among ship rats (Rattus rattus) is scant. Here, we characterize hoarding behavior in ship rats maintained in captivity after capture from the wild. After acclimatization to captivity, 40 ship rats (21 females, 19 males) were presented with baits in experiments designed to emulate a typical poison control operation for vertebrate pests in New Zealand: this involved first offering rats nontoxic cereal baits (of 2- or 6-g size) as a prefeed for three nights consecutively, followed by 6- or 12-g cereal baits laden with 0.15% 1080 on the fourth night. Seventy-eight percent of rats (31/40) hoarded food in distinct cache sites when presented with nontoxic baits although there was no significant effect of bait size or type on hoarding behavior and nor did hoarding behavior vary according to rat gender. When rats were presented with 1080-laden baits, the incidence of hoarding was reduced to 40%, due to the onset of toxicosis. This study indicates that R. rattus will show hoarding behavior analogous to other rat species when presented with an excess of cereal-based baits, at least under conditions of captivity and free from competition. This finding may have practical relevance: since 1080 is the principal toxin used against the major vertebrate pest species in New Zealand (the brushtail possum, Trichosurus vulpecula), ship rats have the potential to deplete supplies of prefeed and/or toxic baits intended for possum control. However, based on typical rat densities recorded in New Zealand native forest (c. 5 rats/ha), the degree of removal and manipulation of toxic baits observed by ship rats here is unlikely to impact adversely on the efficacy of possum control operations.     

Kiore (Rattus exulans) distribution and relative abundance on a small highly modified island

ABSTRACT

Kiore (Pacific rat; Rattus exulans) is both a target for eradication and a taonga or highly valued species in New Zealand, and its abundance and distribution vary considerably throughout the country. We investigated reports of an abundant kiore population on Slipper Island (Whakahau), off the east coast of New Zealand’s North Island, in March 2017. We trapped kiore to examine their distribution across a range of habitats with varying degrees of human activity. Kiore were captured in all habitats, with particularly high abundance at a campground with a fruiting fig tree (50 kiore per 100 trap nights corrected for sprung traps). We found no evidence of other rat species; Slipper Island appears to remain one of few New Zealand islands with kiore but without ship rats (Rattus rattus) and Norway rats (R. norvegicus), the two other rat species present in New Zealand. Slipper Island potentially provides opportunities to research kiore behaviour and population dynamics in a New Zealand commensal environment, and genetics of an isolated island population.     

Impacts of the invasive Argentine ant on native ants and other invertebrates in coastal scrub in south‐eastern Australia

Invasive ants threaten native biodiversity and ecosystem function worldwide. Although their principal direct impact is usually the displacement of native ants, they may also affect other invertebrates. The Argentine ant, Linepithema humile (Dolichoderinae), one of the most widespread invasive ant species, has invaded native habitat where it abuts peri‐urban development in coastal Victoria in south‐eastern Australia. Here we infer impacts of the Argentine ant on native ants and other litter and ground‐dwelling invertebrates by comparing their abundance and taxonomic composition in coastal scrub forest either invaded or uninvaded by the Argentine ant. Species composition of native ants at bait stations and extracted from litter differed significantly between Argentine ant‐invaded and uninvaded sites and this was consistent across years. Argentine ants had a strong effect on epigeic ants, which were either displaced or reduced in abundance. The native ant Rhytidoponera victoriae (Ponerinae), numerically dominant at uninvaded sites, was completely absent from sites invaded by the Argentine ant. However, small hypogeic ants, including Solenopsis sp. (Myrmicinae) and Heteroponera imbellis (Heteroponerinae), were little affected. Linepithema humile had no detectable effect upon the abundance and richness of other litter invertebrates. However, invertebrate group composition differed significantly between invaded and uninvaded sites, owing to the varied response of several influential groups (e.g. Collembola and Acarina). Floristics, habitat structure and measured environmental factors did not differ significantly between sites either invaded or uninvaded by Argentine ants, supporting the contention that differences in native ant abundance and species composition are related to invasion. Changes in the native ant community wrought by Argentine ant invasion have important implications for invertebrate communities in southern Australia and may affect key processes, including seed dispersal.