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Norbormide is a uniquely selective rat toxicant for Rattus species, with rats being 100- to 150-fold more sensitive to norbormide toxicity than most other mammals and birds. Previously we reported that on completion of a 10-year program of targeted fundamental and applied synthetic chemistry and toxicology, taste aversion associated with this compound had been overcome. In 2020-2022, trials have been successfully completed on poultry farms with Norway rats and larger scale field trials were undertaken targeting ship rats using 1% norbormide paste baits. Firstly, the efficacy of norbormide-containing paste baits targeting rat infestations on poultry farms was proven with a 100% reduction of Norway rat populations on three different farms. Secondly, 100% reduction in ship rat abundance was achieved at two large field test sites; and no reduction was achieved at the untreated control site. These larger field trials are described in depth in this publication. Plans are progressing to complete product development and registration.

A non-toxic liquid fertility control bait for rats has recently become commercially available (ContraPest® from SenesTech, Inc.). This product contains two chemicals, both of which impair spermatogenesis in male and reduce ovulations in female rats. We tested the efficacy of this bait in wild-caught adult black rats from the island of Hawai’i in a short-term laboratory trial. A control group (n = 25) was offered placebo bait and the treatment group (n = 25) was offered fertility control bait, both ad libitum, during a 15-day introduction period and during the first of four breeding rounds, for a total of 58 days of exposure. After treatment, all rats were provided placebo bait for the remainder of the study and randomly paired with mates from within their treatment groups for two additional breeding cycles. Treatment and control groups comprised 10 breeding pairs each, with random re-pairings between breeding rounds. The treatment group produced no litters during the first and second breeding rounds, while 70% of the control females produced litters. In the third breeding round, 70 days after stopping treatment, the treatment group produced three litters (six pups) compared to seven litters (24 pups) in the control group. During a fourth and final breeding round, control rats were crossed with treated rats, producing six litters (27 pups) from treated dams and nine litters (40 pups) from control dams, indicating no apparent infertility effect 99 days after cessation of treatment. This study demonstrates that the reproduction rate of wild-caught black rats can be chemically suppressed if provided ad libitum access to the fertility control bait under laboratory conditions.

Invasive ship rats (Rattus rattus) are the major threat to the native species and ecosystem of Goat Island (9.3 ha), New Zealand. The island is only 100 m away from the mainland, which imposes a risk of incursions by rats swimming over. Accessibility depends on weather and tide times which makes regular trap servicing complicated. In 2016 we extended an existing trapping grid of 8 kill traps (DOC200; Department of Conservation, New Zealand) with 10 self-resetting traps (Goodnature A24s; Goodnature Limited, Wellington, New Zealand) to improve current management and ideally achieve eradication. Before our study started, DOC200s on the island had not been serviced for six months. Rats were active even during the day and rat numbers were assumed to be high. The DOC200 kill traps were lured with an egg and A24s were lured with Goodnature automatic lure pumps (ALP) baited with chocolate formula for rats. The A24s were equipped with Goodnature digital strike counters to document the number of rats killed by the self-resetting traps. All devices were on average checked every 49 days from August 2016 to October 2017. DOC200s were reset after triggering or after three months, whichever occurred first. ALPs were replaced in January and July 2017. Gas cartridges of the A24s were replaced when the strike counter showed 20 or more. A substantial number of rats were killed on the island (242 by A24s and 27 by DOC200s) in 8,838 uncorrected trap nights between August 2016 to October 2017 (Table 1). The initial number of individuals killed by A24s in the first month after deployment in August 2016 was high. The number of rats removed by A24s remained at a high level from November 2016 until June 2017. The number of A24 kills varied widely between the beginnings of the breeding seasons across the two years, with 46 individuals killed between September and November 2016 but only 4 kills between August and October 2017. Even though initial trapping success was high, eradication could not be achieved and the self-resetting traps did not perform better than traditional kill traps once rat abundance was low. The Goodnature A24 has shown the potential to work effectively for initial knock-down when rat numbers and activity were high. The advantage over traditional single kill traps, like the DOC200, was the low need for servicing. However, once the population density was reduced to a lower level, this advantage vanished. Most kills by A24s happened during the breeding season in 2016 in the first third of the study. In the last three months of the project the kill numbers did not differ meaningfully from the DOC200 kill numbers. Even though trapping numbers were low, rat abundance was still assumed to be high. After our study had finished rat control on the island using these devices was continued by local community volunteers. A further 357 rats were caught between June 2018 and March 2020, indicating no decline in rat captures. On 1 September 2019 and 1 March 2020 tracking tunnel indices were 100% (K. Tricklebank pers. commun.). In March 2020 initial cost for a DOC200 was NZD$145.00. The purchase costs for a Goodnature A24 with lure and gas for 6 months was NZD$169.00 (excluding digital strike counter). For the first six months the differences in costs were moderate. However, after six months, the material costs for servicing a DOC200 was NZD$0.55 (one freerange egg), or less when using peanut butter. The servicing cost for a Goodnature A24 is NZD$19.00 (gas cartridge + ALP). On Goat Island, servicing costs for a six months period were approximately NZD$9.00 for eight DOC200s and NZD$190.00 for ten A24s. Higher costs for A24 purchase and servicing compared to DOC200 were not compensated by noteworthy higher kill numbers once rat numbers were reduced. However, A24s performed well during peak times and labour costs were not considered in our study. Self-resetting devices at one per hectare did moderately reduce rat numbers in an area where kill trap maintenance was time and cost intensive but suppressing to very low rat numbers or achieving eradication requires additional investment in the system (e.g., a combination of different tools including toxins or a higher density of devices).

On Aotea/Great Barrier Island, New Zealand, two invasive rat species (Pacific rats and ship rats) pose risks to the ecosystems and challenge the management in two sanctuaries. At Glenfern Sanctuary (83 ha) an eradication has successfully removed ship rats and a predator-proof fence prevents reinvasion. However, Pacific rats persist in low abundance. At Windy Hill Sanctuary (770 ha) intensive rodent control maintains both species at low abundance despite ongoing reinvasion. A capture-mark-recapture study was conducted between February and April in 2016 and repeated between July and September 2017 to determine population densities, confirm species composition, and analyse the effects of time, population density, and interspecific competition on rat behaviour. Live traps were monitored with camera traps to analyse behaviour of rats around traps. Population density and detection probability of Pacific rats varied between times reflecting seasonality in food abundance and rat reproduction. The detection probability of Pacific rats also differed between sites, being higher at Glenfern Sanctuary than at Windy Hill Sanctuary, presumably due to interspecific competition with ship rats. Where Pacific rats were the sole species they were captured in traps in the first night. However, in coexistence with ship rats, Pacific rat detection was delayed by at least ten days. Population density influenced the number of trap encounters and interactions but did not significantly influence the capture rate. Interspecific competition was identified as problematic for monitoring, controlling, and eradicating Pacific rats.

Black rats are among the world’s most invasive rodent species and are responsible for considerable agricultural losses and risks to human health through zoonotic disease. In Puerto Rico, rats may also compete with the primary rabies reservoir (the small Indian mongoose) for baits during oral rabies vaccination (ORV) programs. We evaluated black rat population density and home range size on the Cabo Rojo National Wildlife Refuge, southwestern Puerto Rico. We fitted 10 rats with VHF transmitters and tracked them using radio telemetry for approximately 4 weeks. We entered locations into ArcGIS and obtained minimum convex polygon (MCP) home range estimates. We established two plots of 55 snap traps and performed removal for 5 consecutive days during January and July, to correspond roughly with wet and dry seasons for this region. To calculate abundance, we entered snap trap data using a removal model approach in Program MARK. We calculated the effective trapping area by creating a buffer around the trapping area based on the square root of mean home range estimate. We divided the abundance calculated in MARK by the effective trapping area to calculate the estimated population density. Mean MCP home range estimate was 0.28 ha (SE: 0.05, range: 0.07-0.50 ha). Population density estimates were 114.7 (SE: 201.80) and 19.3 (SE: 6.85) per ha for January and July, respectively. To reduce the potential for rat consumption of ORV baits, wildlife managers should consider conducting ORV activities in Puerto Rico during periods of lower rat abundance or density.

Despite the black rat being the most common invasive rat on tropical islands, little is known about habitat selection and seasonal changes in density on atolls. On Aldabra Atoll, a UNESCO World Heritage site in the Seychelles, Indian Ocean, black rats occur in all available forest types, including mangrove forest, at high densities. Mangrove forest appears to be particularly good habitat with larger recorded body sizes, larger juveniles, and in better body condition than rats trapped in ‘terrestrial’ forest. Any plans for black rat eradication on large islands with mangrove forest will be thwarted by the presence of rats in this habitat, where poison bait is unlikely to be aerially laid successfully due to tidal inundation.

Three rat species, the Norway rat, black rat or ship rat, Pacific or Polynesian rat, and the house mouse are among the most widespread and destructive invasive mammals affecting islands. Through mostly unintentional introductions by humans, these rodents occupy >80% of the major islands worldwide. As a consequence of their omnivorous diet and large incisor teeth, introduced rats are probably the invasive animals responsible for the greatest number of plant and animal extinctions on islands. The effects of house mice on island ecosystems are less well known when compared with rats. We have reviewed past diet studies of these 4 omnivorous rodent species. Our review suggests that due to the high variability in diet, as well as direct and indirect effects of predation, all 4 species pose potential threats to many plants and animals on Pacific islands. Although rodent diets greatly differ among sites, diets appear to roughly follow this pattern: Norway rats and house mice generally consume proportionally more animal than plant (Norway rats consume many vertebrates and house mice mostly consumes arthropods), whereas black and Pacific rats generally consume proportionally more plant than animal. Studies specifically linking rodent diets with the population status of surrounding biota are needed in order to clarify the effective impacts of these rodent species. Much could be learned from rodent removal experiments, which could further expand our knowledge of invasive rodent species effects, and native species conservation, on islands.

Black rats have been on Anacapa Island for close to 100 years and pose a threat to the biodiversity of the island. Removing non-native rats from an island is a powerful conservation tool. There have been numerous attempts to eradicate rats from Anacapa: 2001/2002 marked the first successful eradication of invasive rodents from an entire island where an endemic rodent was present, and the first aerial application of rodenticides in North America.

Introduced black rats are among the most invasive species to islands worldwide. In addition to agricultural impacts, rats are vectors of disease, cause damage to native flora and fauna, and negatively impact threatened/endangered species. Eradication efforts have met with mixed success. Success or failure of an eradication effort can depend on the population density of the target species, which can influence rodenticide sowing rates. We used snap trapping grids to estimate black rat densities in two different forest types on Diego Garcia: coconut forest and mixed species forest. Individual snap traps baited with fresh coconut were placed every 10 m in a 100-m × 100-m (1 ha) grid in the mixed forest and every 20 m in a 220-m × 220-m grid (4.8 ha) in the coconut forest. Traps were checked twice daily for 7 and 11 days in the mixed and coconut forest, respectively. In total, 914 rats were captured on the coconut forest grid and 125 rats were captured on the mixed forest grid. Rat density in coconut forest was 187 rats/ha (95% CI: 176-201) and 88 rats/ha (95% CI: 82-104) in mixed forest. Stomach contents were examined in 121 rats trapped in the mixed forest: 81% contained coconut along with other vegetation or meat, and 67% contained coconut exclusively. It is likely that the high rat density is driven by an abundant coconut food source resulting in a variable distribution of rats among habitat types. Planning for eradication will need to consider the variability of rodent densities across different habitats, with management strategies developed to address this variability.

Introduced rats continue to have a major impact on biodiversity around the world, and improved control techniques are required to avoid further extinctions. We are trialing re-setting toxin-delivery systems (Spitfires) targeting a range of predators, including rats. The rat Spitfire works by firing 800 mg of a toxic paste onto the belly of the rat as it passes through a tunnel; the device then resets. When the rats groom the paste from their fur, they ingest the toxin. Each Spitfire is capable of approximately 100 doses and is fitted with a counter and a delay mechanism. We trialed 0.55% 1080 paste in the Spitfire and 15 of 15 wild Norway rats and 14 of 15 black rats died. Further trials are planned with a range of toxins to allow flexibility of use. Resetting devices that are expected to work for long periods without being serviced also require long-life lures. Preliminary trials showed urine and scats from female Norway rats were attractive to both male and female Norway rats. The volatile components from these and further trials will be identified to aid in developing a long-life lure. The long-term, effective control of introduced rats will require a range of toxins with different modes of action, a number of different delivery systems, and long-life lures.

Palmyra Atoll National Wildlife Refuge is a moist Central Pacific atoll that supports one of the best remaining tropical forest ecosystems in the region, including 10 species of breeding seabirds and a robust population of the world’s largest terrestrial invertebrate, the coconut crab. Despite these riches, the atoll’s ecosystem has been modified by introduced black rats that were inadvertently brought to Palmyra during WWII. Between June 1 and 30, 2011, a partnership between the U.S. Fish and Wildlife Service, The Nature Conservancy, and Island Conservation successfully implemented a project to remove rats from Palmyra. Independent monitoring of bait application and its environmental effects was undertaken by the USDA. Over the 28-day operation, a team of 41 people from 5 countries utilized 2 helicopters, 10 slingshots, 148 bait stations, and hand spreading to strategically apply 38,561 kg of rodent bait containing the anticoagulant brodifacoum (25 ppm) to Palmyra’s 235 hectares of emergent land. Palmyra’s challenging eradication environment demanded the development of a novel approach, such as broadcast application rates between 75 and 85 kg/ha and the use of “bolas” to bait coastal forest canopy to minimize bait drift into the marine environment. Initial findings show minimal non-target impacts as a result of the project, and post-eradication monitoring has failed to detect rats. Increased recruitment by at least 2 native tree species has been observed. By removing rats from Palmyra, the partnership aims to safeguard the atoll’s indigenous flora and fauna, encourage the reestablishment of extirpated seabird species, and create an ecological refuge for species within the Central Pacific region that are at risk of extinction. This project is a conservation milestone for the Refuge, and it has established a benchmark for eradication campaigns on other tropical islands.

Between June 1 and 30, 2011, a partnership between the U.S. Fish and Wildlife Service, The Nature Conservancy, and Island Conservation successfully implemented a project to remove introduced black rats from Palmyra Atoll National Wildlife Refuge. Prior to the rat eradication, we assessed several environmental risk factors associated with the application of an anticoagulant rodenticide to Palmyra’s emergent land area. Here, we present the findings from a study of toxicant migration from bait pellets into topsoil. Topsoil from plots characterized as “sandy” or “humus” was collected after exposure to bait pellets containing 50 ppm of diphacinone or 25 ppm of brodifacoum. Brodifacoum and diphacinone were detected in samples of both sandy and organic topsoil while control samples collected outside of the study plots tested negative for both toxicants. With both toxicants, residue concentrations decreased with time and neither toxicant was detected in most of the 28, 36, and 50-day samples; trace amounts (=0.2 ppm for brodifacoum and =2 ppm for diphacinone) of the toxicants were detected in a few samples from these groupings. We did not find a significant difference in toxicant concentrations between the two types of topsoil. The results from this study suggest that following a broadcast of rodenticide across Palmyra’s emergent land area, small amounts of brodifacoum or diphacinone would migrate to, and remain in, Palmyra’s topsoil for a short period of time.

We monitored natural and artificial nests during a two-part study on East Maui, Hawaii, designed to examine factors influencing nest depredation by black and Polynesian rats. The first half of the study examined the effects of rat control on nest depredation within portions of the Hanawi Natural Area Reserve. Rat density monitoring indicated control efforts had significantly reduced black rat captures in treatment areas, but no differences in survival of artificial or natural nests between treatment and control areas were observed. The second half of the study examined the effect of nesting substrate on nest depredation in the Makawao Forest Reserve during June 2003 and June 2004. We chose fruiting and non-fruiting nest substrates for artificial nests in two habitat types, native ohia/koa forest and an adjoining forest dominated by non-native tropical ash. Results from snap trapping showed that the relative density of black rats was significantly higher in the ohia/koa forest than the tropical ash forest, but plots with more rat captures did not always have higher rates of nest depredation as predicted. Our findings suggest that there is a large degree of variability in nest depredation by Rattus spp., but that rat density, forest type, and nest substrate influence nest depredation rates.

The susceptibility of eight rodent species to a range of widely used and candidate rodenticides was determined in laboratory feeding tests. No choice and choice tests were used to assess toxicity and effect on palatability of the rodenticides to Meriones shawi (Shaw's gerbil), Arvicanthis niloticus (Nile rat), Acomys cahirinus (Egyptian Spiny mouse), Mastomys natalesis (Multumammate rat), Sigmodon hispidus (Cotton rat), Rattus exulans (Polynesian rat), and R. rattus (Ship rat) which responded differently to each chemical. The results of these tests suggest possible rodenticides suitable for control of each species. Field trials are now needed to assess the effectiveness of these compounds under practical conditions.

In view of resistance reported to have developed towards second generation anticoagulants and the problem of bait shyness and neophobia when acute rodenticides are used, it becomes imperative that methods be evolved to overcome these problems. Attempts to potentiate anticoagulants for effective rodent control is a new concept with very few studies. Experiments using two non-steroid ant-inflammatory drugs, namely ibuprofen and phenylbutazone at 80 mg/kg and 50 mg/kg body weight respectively to potentiate the action of two second generation anticoagulants, brodifacoum and bromadiolone, yielded positive results for Rattus rattus. The drugs reduced the lethal dose required for 100% mortality as well as days to death. Field trials confirmed laboratory findings.

Black rats (Rattus rattus) have begun occupying a new habitat in recent years —the Jerusalem pine (Pinus halepensis) forests in Israel. In this, otherwise almost sterile habitat, the sole source of nourishment for the rats is the pine seems that can only be extracted from the cones through a complex feeding technique. Adult black rats unfamiliar with the technique (termed "naive") were unable to attain it either through trial and error or through observational learning when housed with experienced rats (termed "strippers"). In contrast, black rat pups raised by stripper mothers did learn the pine cone opening behaviour. In addition to the presence of a stripper model, however, the clues of the pine seeds themselves, as well as partially open cones, may also play a role in the acquisition of the technique. The state of the cone itself, when encountered by the rat pups, may be an important factor. Three groups of experimental animals were used: 25 pups born to naive mothers and reared on rat chow without exposure to either stripping mothers or partially opened cones; 25 pups born to naive mothers and exposed to pine cones in various stages of opening; 55 pups born to stripper mothers and exposed both to pine cones and to the presence of their mothers actively involved in stripping the cones and feeding on the seeds. We found that pine cone stripping behaviour is learned through two stages of a local enhancement effect: First, the pups are directed to the pine cones as a food resource, and then to the cone's proximal end as a starting point. The development of the stripping technique is acquired individually, with accumulating experience.

This work compares object replacement and object presentation as causes of avoidance (new object reaction or neophobia). The movements of wild black rats, Rattus rattus, living in an automated plus maze were recorded (1) after replacing a familiar object (in a familiar place) with a series of novel objects, (2) after presenting a novel object in a familiar place where there had been no object. Replacing one object by another did not delay entry to the maze arm containing it. In contrast, the presence of a new object in a previously empty arm did increase the latency of the first approach (new object reaction), although after the first entry, the rate of visiting the arms and the time spent in them, which are measures of subsequent approach, were unaffected. Hence, this form of neophobic behavior was evoked only by the presence of a new object where none had been before. Differences with earlier reports can be resolved in most cases when attention is paid to the difference between presentation and replacement.

Based on findings from studies conducted in the Philippines over a span of almost a decade, primarily by scientists at the Philippine National Crop Protection Center, crown-baiting (wherein bait containing anticoagulant is placed monthly in the crowns of some palms in a coconut plantation), holds the potential of providing highly economical protection from rat damage. The success of the method in various field trials appeared related, in part, to selective removal of rodents that feed in the palms and to the use of baits that were preferred over growing nuts. Studies have also indicated that only 10% or less of the trees may have to be baited for effective control, although additional field trials are needed to confirm the optimal levels of treatment for different coconut-growing regions in the Philippines. Based on findings from the studies, fallen, rat-damaged nuts may represent only a small portion of the damage that rats inflict on coconut palms in the Philippines.

The island of Barbados, in the eastern Caribbean, experienced an increase in the number of cases of leptospirosis between 1961 and 1971. With assistance from Pan American Health Organization/World Health Organization, multiple surveys were done to determine cause of the problem. The surveys concluded that (1) most cases of leptospirosis occurred just after heavy rainfall; (2) persons in the low socio-economic groups were more prone to acquire the disease; (3) rats (Norway rat, Rattus norvegicus, and black rat, R. rattus) were the major reservoir of leptospira organisms, with approximately one in three rats examined positive for leptospira organisms; and (4) persons performing specific types of work were the ones who are most frequently infected (e.g. farm, cane, and abattoir workers). The accomplishments of the newly-established Rodent Control Unit are described. After four years of operation, Barbadians are more aware of the rodent problem in the island today, as compared to the pre-Unit era, when rats and mice were commonly seen in public markets, bonds, warehouses, institutions, and dock areas. Today, in spite of the numerous eating places, stores, food and feed plants, etc., the rodent problem is relatively minor as compared with the past. The public is also more aware of the potential problems with rodents, and therefore quickly seeks help from the Rodent Control Unit. A systematic approach to rodent control has been achieved. Anticoagulant rodent baits (liquid and solid) are used extensively in the control work. Rodent Control work in Barbados is an ongoing process and is second-to-none in the Caribbean.

Brodifacoum was fed to three rodent species, viz . M. hurrianae, R. rattus and F. pennanti, using a no-choice feeding trial for 7 days at various concentrations− 0.005%, 0.0025%, and 0.00125%. The compound was found effective, palatable, developed no sign of poison bait-shyness but indicated a slight aversion of poison. The death of the animals was due to pulmonary distress and hemorrhage.

The East African nations of Ethiopia, Somalia, Kenya, Uganda, Tanzania, Malawi, Mozambique, and Zimbabwe encompass a widely varied topography, and climate from tropical to temperate. Where soil and rainfall permit, agricultural crops are grown. For the most part, farming is of a subsistence nature being small single family plots, which make up about 90% of the farming in these nations. Large farms in Kenya and Zimbabwe are generally confined to the temperate uplands, and elsewhere there are large government agricultural schemes growing food crops like rice and sugar cane. Almost all of the nations of East Africa have chronic food shortages. The impacts of the most economically important rodent species, including the multimammate mouse, grass rat, Norway rat, roof rat, and house mouse, as well as these species biology, are summarized. A 2-year rodent control program in Somalia, funded by FAO, began in 1981 and is briefly described, as are recent rodent control projects in other East African countries. A positive outcome of these projects is that they have incorporated education for responsible national staff who in turn will train fellow workers. Long-term support for such efforts is needed.

Trapping is usually considered a rodent control technique of minor importance. Due to the economic situation in the Dumaguete, Philippines programme from which this report is drawn, regular trapping was a biological necessity. Four species of rodents and a shrew were of concern. A continuing daily trapping programme was developed from a field study of trap bait acceptability. Trap baits were reused every 23 days. Alternate baits were selected. Trap usage techniques were designed to optimize the results. Trap-bait shyness and trap shyness effects were observed but were not a major problem.

Heavy losses In Hawaiian sugarcane are caused by Polynesian rats (Rattus exulans), Norway rats (R. norvegicus), and black rats (R. rattus). Relative population levels, movement patterns, damage to sugarcane, and suggested timing of control during five stages of the 2-year crop cycle are described. The progress toward the registering of zinc phosphide for use in crops and the development of other rodenticides are mentioned.

Past and present concepts of rodent control at the 24 sugar plantations of Hawaii are reviewed with particular attention being given to the research efforts of the Experiment Station of the Hawaiian Sugar Planters Association in improving operational rodent control in sugarcane. Hawaii offers a unique set of conditions: a 2-year crop cycle, a production of over 100 tons of sugarcane per acre, countless numbers of gulches and wasteland bordering crop fields, and a year-long growing season, all having an effect on rat population and habitat.