Natal nest locations of the Asian house rat (Rattus tanezumi) in lowland rice–coconut cropping systems: a coconut penthouse or rice bunds with water frontage?

Context Rattus tanezumi is a serious crop pest within the island of Luzon, Philippines. In intensive flood-irrigated rice field ecosystems of Luzon, female R. tanezumi are known to primarily nest within the tillers of ripening rice fields and along the banks of irrigation canals. The nesting habits of R. tanezumi in complex rice–coconut cropping systems are unknown. Aims To identify the natal nest locations of R. tanezumi females in rice–coconut systems of the Sierra Madre Biodiversity Corridor (SMBC), Luzon, during the main breeding season to develop a management strategy that specifically targets their nesting habitat. Methods When rice was at the booting to ripening stage, cage-traps were placed in rice fields adjacent to coconut habitat. Thirty breeding adult R. tanezumi females were fitted with radio-collars and successfully tracked to their nest sites. Key results Most R. tanezumi nests (66.7%) were located in coconut groves, five nests (16.7%) were located in rice fields and five nests (16.7%) were located on the rice field edge. All nests were located above ground level and seven nests were located in coconut tree crowns. The median distance of nest sites to the nearest rice field was 22.5 m. Most nest site locations had good cover of ground vegetation and understorey vegetation, but low canopy cover. Only one nest location had an understorey vegetation height of less than 20 cm. Conclusions In the coastal lowland rice–coconut cropping systems of the SMBC, female R. tanezumi showed a preference for nesting in adjacent coconut groves. This is contrary to previous studies in intensive flood-irrigated rice ecosystems of Luzon, where the species nests mainly in the banks of irrigation canals. It is important to understand rodent breeding ecology in a specific ecosystem before implementing appropriate management strategies. Implications In lowland rice–coconut cropping systems, coconut groves adjacent to rice fields should be targeted for the management of R. tanezumi nest sites during the main breeding season as part of an integrated ecologically based approach to rodent pest management.

Can media campaign messages influence change towards ecologically based rodent management?

Context In Asia, losses to rodents contribute to the undernourishment of smallholder families. Ecologically based rodent management (EBRM) has become the national policy for rodent management in rice-based agriculture in Indonesia, the Philippines and Vietnam. EBRM requires community action. Therefore we need to develop communication campaigns that increase community involvement in rodent management. Aims This study evaluates the effects of a campaign to promote EBRM in a community that suffers chronic rodent losses to their rice crop. We hypothesised that the campaign would create changes in rodent management by farmers based on key messages delivered. Methods We documented existing beliefs and management practices, and captured changes in knowledge, attitudes and behaviour of smallholder farmers after the campaign. We also document benefits to the community. We used qualitative tools to evaluate existing beliefs and management practices of rodents in nine villages in Zaragosa, one of which was a focus village for the campaign. Key results Farmers who were influenced by the campaign had significantly higher mean rank scores in knowledge and attitudes pertaining to key messages of the campaign, such as working together, proper timing of management actions, and that rodents can be controlled. Farmers who heard the campaign obtained yields that were higher by 0.7 t ha–1 compared with those with no exposure to the campaign. A year after the campaign, the increase in rice yield in Zaragosa was sufficient to feed 1375 adult Filipinos for a year. The campaign influenced policy on rodent management in Zaragosa and subsequently at the provincial level. Conclusions A media campaign with support from local leaders and extension staff is an effective way to disseminate EBRM, leading to positive economic benefits for smallholder farmers. A media campaign alone is less effective. Implications A communication campaign on EBRM with follow-up support from extension experts is a highly effective pathway for changing attitudes and practices of smallholder farmers on rodent management, and for effective dissemination of EBRM.

Can humans outsmart rodents? Learning to work collectively and strategically

Context Rodents are one of the major constraints in Asian rice production, both in pre- and post-harvest. Rodents are often perceived by farmers in developing countries to be consistently outsmarting humans – a belief that needs to be overcome. Ecologically based rodent management (EBRM) is a possible solution to manage rodent populations effectively, which in turn can help sustain food security in Asia. Well coordinated community action is necessary to effectively carry out EBRM. This paper considers the socio-cultural challenges of EBRM. Aims To determine whether a multi-stakeholder partnership, facilitated through experiential learning and the use of existing social capital, can generate collective actions for strategic rodent management. Methods Participatory action research was employed in the implementation of EBRM in irrigated rice systems in the Red River Delta in Vietnam. Both quantitative and qualitative methods were used including household surveys, focus group discussions and key informant interviews. Key results The multi-stakeholder partnership and participatory approach effectively generated adoption of EBRM. The strong linkages between extension and political organisations generated diffusion of EBRM into neighbouring provinces. The adoption of EBRM reduced rodenticide use (50%), decreased rice areas with rodent damage (93%), increased rice yields (10–14%), increased economic returns for farmers (20%), strengthened farmers’ collective actions, and changed farmers’ perspectives on rodent management towards a biologically sustainable approach. Conclusions Humans can indeed outsmart rodents through the use of EBRM principles that rely on community actions. Sustainable community actions can be achieved through participatory approaches and a multi-stakeholder partnership built on existing social capital of the society and local communities. Overall, the adoption of EBRM meant better rice yields, higher economic returns for farmers, and reduced human health and environmental risks. Implications To address the problem of sustainable adoption by farmers of an agricultural technology for natural resource management, active participation of various stakeholders through a multi-stakeholder partnership is essential. This partnership should emanate from the social capital of the society, such as the networks of organisations across different scales, from the national to the village level, and the cultural norms and values adhered to by the members of the society and local communities.

Impacts of rodent outbreaks on food security in Asia

Since 2007, a spate of rodent outbreaks has led to severe food shortages in Asia, affecting highly vulnerable and food-insecure families. Little has been documented about wildlife-management issues associated with these outbreaks. The aims of the present study were to synthesise what we know about rodent outbreaks in Asia, and identify important gaps in our knowledge. We compiled information from agencies of the United Nations, non-government organisations and the authors. The authors conducted site visits to areas affected by outbreaks of rodent populations, and convened an international conference in October 2009 to share knowledge. Bamboo masting is clearly implicated as the primary cause of the rodent-population outbreaks that led to severe food shortages in Mizoram (India), Chin State (Myanmar), Chittagong Hill Tracts (Bangladesh) and upland provinces of Lao PDR. In Laos, emergency food assistance was required for 85 000–145 000 people. In 2009, high rodent losses occurred also in lowland irrigated rice-based systems in the Philippines, Myanmar and Indonesia, not related to bamboo masting. Asynchronous or aseasonal growing of rice crops was a common element in these outbreaks. In the Ayeyarwaddy delta, Myanmar, 2.6 million rats were collected in 3 months through community activities; this outbreak appeared to be related to an extreme climatic event, Cyclone Nargis. There are two key features of rodent outbreaks that make the future uncertain. First, climate change and extreme climatic events will increase impacts of rodents on agricultural production. Second, there is food-security pressure in some countries to grow three crops per year. Increased cropping intensity will reduce fallow periods and create ideal conditions for rodents to breed nearly continuously. Implications of the research are as follows: (i) rodent outbreaks are a consequence of enhanced reproduction and natural mortality is of minor importance, particularly with rapidly increasing populations; therefore, we need to focus more on methods for disrupting reproduction; (ii) a stronger understanding of the ecology of pest species and community dynamics will enable ecologically sustainable management; (iii) we need landscape approaches that focus on crop synchrony, and timely coordinated community action to manage pest species and conserve desirable species; and (iv) a simple monitoring system can help implement ecologically based rodent management.

Ecologically based management of rodents in lowland irrigated rice fields in Indonesia

Context. Overabundant rodents cause considerable crop damage and, in developing countries of South-east Asia, rodents can be an obstacle to attempts at alleviating poverty. Management is often based on the use of chemicals that can harm non-target species. Therefore, an effective and environmentally benign management approach such as ecologically based rodent management (EBRM) is desirable. Aims. We compared the effectiveness of EBRM to that of conventional management on populations of rice-field rats (Rattus argentiventer). Methods. The study was conducted as a large-scale replicated field trial in lowland irrigated rice fields in West Java, Indonesia. EBRM actions included habitat manipulations, removal of rats with trap barrier systems, coordinated rat-control campaigns and synchrony of cropping on the village level. We measured abundance, population structure, and breeding of rice-field rats as well as rice production and crop damage caused by rats. Key results.Although there was no overall effect of the EBRM treatment on rat abundance, we found decreasing rat abundance in rice-field habitats at the late cropping stage in treated villages and a decrease in body size of rats. In addition, we found fewer reproducing females when EBRM was applied than with the application of conventional methods, whereas male reproductive condition did not decrease. Overall, there was a reduction in mean crop damage when EBRM was applied (4.4 ± 0.4% in treatments v. 2.5 ± 0.4% in experimental controls), which translated into 6% higher rice production. Conclusions. The results demonstrated that EBRM is an appropriate approach to manage overabundant rodents in irrigated lowland rice-based agro-ecosystems and possibly in other agro-ecosystems. This will provide substantial benefits for smallholder farming communities in developing countries and most likely benefits for ecosystem health. Implications. The EBRM approach should be used routinely in irrigated lowland rice crops that are at risk of damage by rice-field rats.

The Year of the Rat ends - time to fight hunger!

This paper investigates the importance of ecologically based rodent management in the light of the current food crisis, and the potential effects of this approach on the position of the undernourished. Hunger and food prices are on the rise owing to shortages that can be traced to reasons such as climatic extremes, use of crops for biofuels, reduced growth in yields which lag behind population growth, reduced world stocks and lack of sufficient investment in maintaining the irrigation infrastructure. For the undernourished this is problematic as they are most vulnerable to the rise in food prices. Very often, agricultural experts focus on an increase in agricultural production to reduce food prices. It is postulated in this article that almost 280 million undernourished could additionally benefit if more attention were paid to reducing pre- and post-harvest losses by rodents. Moreover, rodent-borne diseases would decrease, diseases that can be catastrophic to the livelihoods of the poorest of the poor.

Fertility control of rodent pests

Ricefield rats (Rattus argentiventer) in south-east Asian rice fields and house mice (Mus domesticus) in Australian grain fields are major pest species. They cause damage before and after harvest and carry zoonotic diseases. For both species, management techniques have been pursued using the approach of immunocontraceptive vaccination. We review results from a series of enclosure and field studies conducted with these species to assess the effects of fertility control in small rodents. In the experiments, fertility control was simulated by tubal ligation, ovariectomy or progesterone treatment. A once-off sterilisation of 50–75% of enclosed founder females considerably reduced reproductive output of ricefield rat populations until the end of the reproductive period. In house mice, similar success was achieved when a sterility level of 67% of female founders and offspring was maintained. Repeated antifertility treatments are required because of the much longer breeding period of house mice versus ricefield rats. Comparing the results of enclosure trials with the outcome of simulation models suggests that partial compensation of treatment effects can occur through enhanced reproduction of the remaining fertile females and improved survival of juveniles. However, such compensatory effects as well as behavioural consequences of sterility in field populations are not likely to prevent the management effect at the population level. The challenge for effective fertility control of small rodents in the field is the wide-scale delivery of an antifertility treatment to founders at the beginning of the breeding season and to fertile immigrants that are recruited into the population, which otherwise contribute to the reproductive output at the population level. Future research efforts should focus on species-specific techniques and on agents that can be effectively delivered via bait.

Ecologically based management of rodents in the real world: applied to a mixed agroecosystem in Vietnam

Rodents cause significant damage to lowland irrigated rice crops in the Red River Delta of Vietnam. A four-year study was conducted in 1999-2002 to examine the effectiveness of applying rodent control practices using the principles of ecologically based pest management. Four 100-150 ha study sites adjacent to villages were selected and farmers on two treated sites were asked to follow a set of rodent management practices, while farmers on the untreated sites were asked not to change their typical practices. Farmers on the treated sites were encouraged to use trap-barrier systems (TBS's; 0.065-ha early planted crop surrounded by a plastic fence with multiple capture traps; one TBS for every 10-15 ha), to work together over large areas by destroying burrows in refuge habitats soon after planting (before the rats reestablish in the fields and before the onset of breeding), synchronizing planting and harvesting of the their rice crops, cleaning up weeds and piles of straw, and keeping bund (embankment) size small (<30 cm) to prevent burrowing. A 75% reduction in the use of rodenticides and plastic barrier fences (without traps or an early crop) was achieved on treated sites. The abundance of rodents was low after implementation of the management practices across all sites. There was no evidence for an effect of treatment on the abundance of rodents captured each month using live-capture traps, and no difference in damage between treatments or in yields obtained from the rice crops. Therefore, ecologically based rodent management was equally effective as typical practices for rodent management. Farmers on the treated sites spent considerably less money applying rodent control practices, which was reflected in the comparative increase in the partial benefit:cost of applying ecologically based rodent management from 3:1 on treated sites and untreated sites prior to the implementation of treatments to 17:1 on treated sites in the final year of the project.

Self-regulation within outbreak populations of feral house mice: a test of alternative models

1. Outbreaks of feral house mice, Mus domesticus, in Australia represent a fundamental failure of the behavioural control mechanisms of population density, as proposed in the hypothesis of self-regulation. 2. Mice have the potential to keep numbers in check via a suite of spacing behaviours; however, the self-regulation hypothesis implies that some social change occurs that permits the population to erupt. It also suggests that at different phases of an outbreak, distinct patterns of social activity are evident. 3. We compare predictions from two models encapsulating the self-regulation hypothesis as applied to feral house mice in south-eastern Australia. Each model may be distinguished by the timing of aggressiveness between mice that leads to a closed social system. We compare individual turnover, residency and territoriality in each sex and age cohort during the increase, peak and low phases of a population outbreak that peaked in 2001. 4. The activity of 438 mice was monitored via intensive mark-recapture trapping and an automated event recording system that detected the activity of 300 marked individuals at burrow entrances. 5. Our findings support the second model, which suggests that mice switch from an almost asocial structure at low densities to a territorial system as abundance increases. Adult females appear more likely than males or juveniles to make the significant social shift. The trigger for this change remains unclear and several alternative mechanisms are proposed.

Estimating the abundance of mouse populations of known size: promises and pitfalls of new methods

Knowledge of animal abundance is fundamental to many ecological studies. Frequently, researchers cannot determine true abundance, and so must estimate it using a method such as mark-recapture or distance sampling. Recent advances in abundance estimation allow one to model heterogeneity with individual covariates or mixture distributions and to derive multimodel abundance estimators that explicitly address uncertainty about which model parameterization best represents truth. Further, it is possible to borrow information on detection probability across several populations when data are sparse. While promising, these methods have not been evaluated using mark-recapture data from populations of known abundance, and thus far have largely been overlooked by ecologists. In this paper, we explored the utility of newly developed mark-recapture methods for estimating the abundance of 12 captive populations of wild house mice (Mus musculus). We found that mark-recapture methods employing individual covariates yielded satisfactory abundance estimates for most populations. In contrast, model sets with heterogeneity formulations consisting solely of mixture distributions did not perform well for several of the populations. We show through simulation that a higher number of trapping occasions would have been necessary to achieve good estimator performance in this case. Finally, we show that simultaneous analysis of data from low abundance populations can yield viable abundance estimates.

Kin interactions and changing social structure during a population outbreak of feral house mice

Populations of feral house mice (Mus domesticus L.) in Australia undergo multiannual fluctuations in density, and these outbreaks may be partly driven by some change in behavioural self-regulation. In other vertebrate populations with multiannual fluctuations, changes in kin structure have been proposed as a causal mechanism for changes in spacing behaviour, which consequently result in density fluctuations. We tested the predictions of two alternative conceptual models based on kin selection in a population of house mice during such an outbreak. Both published models (Charnov & Finerty 1980; Lambin & Krebs 1991) propose that the level of relatedness between interacting individuals affects their behavioural response and that this changes with population density, though the nature of this relationship differs between the two models. Neither of the models was consistent with all observed changes in relatedness between interacting female mice; however, our results suggested that changes in kin structure still have potential for explaining why mouse outbreaks begin. Therefore, we have developed a variant of one of these conceptual models suggesting that the maintenance of female kin groups through the preceding winter significantly improves recruitment during the subsequent breeding season, and is therefore necessary for mouse outbreaks. We provide six testable predictions to falsify this hypothesis.

Transmission of two Australian strains of murine cytomegalovirus (MCMV) in enclosure populations of house mice (Mus domesticus)

To control plagues of free-living mice (Mus domesticus) in Australia, a recombinant murine cytomegalovirus (MCMV) expressing fertility proteins is being developed as an immunocontraceptive agent. Real-time quantitative PCR was used to monitor the transmission of two genetically variable field strains of MCMV through mouse populations after 25% of founding mice were infected with the N1 strain, followed by the G4 strain 6 weeks later. Pathogen-free wild-derived mice were released into outdoor enclosures located in northwestern Victoria (Australia). Of those mice not originally inoculated with virus, N1 DNA was detected in more than 80% of founder mice and a third of their offspring and similarly, G4 DNA was detected in 13% of founder mice and in 3% of their offspring. Thus, prior immunity to N1 did not prevent transmission of G4. This result is promising for successful transmission of an immunocontraceptive vaccine through Australian mouse populations where MCMV infection is endemic.

The potential of Capillaria hepatica to control mouse plagues

The potential of helminths as bio-control agents of mammalian pests has been largely ignored. However, the nematode Capillaria hepatica is currently being examined for its potential to control population outbreaks of house mice in Australia. Grant Singleton and Hamish McCallum discuss laboratory and ecological studies of the parasite and host, and describe the results of two models that explore the interaction between C. hepatica and mouse populations.

Can farm-management practices reduce the impact of house mouse populations on crops in an irrigated farming system?

The impacts of a range of farm-management practices on house mouse (Mus domesticus) populations were tested in a large replicated field study in a complex irrigated farming system in southern New South Wales, Australia. An advisory panel, made up of farmers, extension officers, industry representatives and scientists developed a series of best-practice farm-management actions to minimise the impact of mice. Twelve experimental sites were split into six treated sites, where farmers were encouraged to conduct the recommended practices, and six untreated sites, where farmers conducted their normal farming practices. Mouse abundance was generally low to moderate for the 4-year project (5–60% adjusted trap success). We found significant reductions in population abundance of mice on treated sites when densities were moderate, but no differences when densities were low. Biomass of weeds and grasses around the perimeter of crops were significantly lower on treated sites because of applications of herbicide sprays and grazing by sheep. We could not detect any significant difference in mouse damage to crops between treated and untreated sites; however, levels of damage were low (<5%). Yields of winter cereals and rice crops were significantly higher on treated sites by up to 40%. An analysis of benefits and costs of conducting farming practices on treated sites compared with untreated sites showed a 2 : 1 benefit to cost ratio for winter cereals, 9 : 1 for rice and 4 : 1 for soybeans.

Can outbreaks of house mice in south-eastern Australia be predicted by weather models?

Outbreaks of house mice (Mus domesticus) occur irregularly in the wheat-growing areas of south-eastern Australia, and are thought to be driven by weather variability, particularly rainfall. If rainfall drives grass and seed production, and vegetation production drives mouse dynamics, we should achieve better predictability of mouse outbreaks by the use of plant-production data. On a broader scale, if climatic variability is affected by El Niño–Southern Oscillation (ENSO) events, large-scale weather variables might be associated with mouse outbreaks. We could not find any association of mouse outbreaks over the last century with any ENSO measurements or other large-scale weather variables, indicating that the causal change linking mouse numbers with weather variation is more complex than is commonly assumed. For the 1960–2002 period we were only partly successful in using variation in cereal production to predict outbreaks of mice in nine areas of Victoria and South Australia, and we got better predictability of outbreaks from rainfall data alone. We achieved 70% correct predictions for a qualitative model using rainfall and 58% for a quantitative model using rainfall and spring mouse numbers. Without the detailed specific mechanisms underlying mouse population dynamics, we may not be able to improve on these simple models that link rainfall to mouse outbreaks.

Is reproduction of the Australian house mouse (Mus domesticus) constrained by food? A large-scale field experiment

Food quantity and especially food quality are thought to be key factors driving reproductive changes in the house mouse, Mus domesticus, leading to outbreaks of house mouse populations in the Australian grain-growing region. Characteristic changes during an incipient mouse plague are an early start of breeding, a high proportion of females breeding at a young age and a prolonged breeding season. We conducted a large-scale food manipulation during an incipient mouse plague, which started with early breeding and relatively high spring numbers of mice. We measured background food availability in four farms throughout the study and conducted a food manipulation experiment from November to March in two of them. After harvest in December 100-200 kg/ha spilled grain remained in the stubble. This was depleted by March. In two treatment farms we added high-protein food pellets on a weekly basis between November and March and two farms served as controls. We measured changes in mouse numbers by capture-mark-recapture trappings and changes in reproduction by scoring embryos and recent placental scars at necropsy. Mouse numbers did not differ between treatments and controls. There were no differences in the litter size or the proportion of females breeding between treatments and controls. We observed the normal pattern of high litter size in spring and decreasing litter size towards the end of summer in treatments and controls. In all farms reproduction stopped in March. Mouse numbers were high but not at plague densities. Contrary to our prediction we did not observe food constraint affecting the reproduction of female mice. Our field experiment seems to rule out food quality as the driving factor for improved reproduction and formation of an outbreak of mice. We suggest that physiological mechanisms in mice might not enable them to take advantage of food with a high protein content in arid summers in southeastern Australian grain fields because of the lack of free-standing water.

Ecological basis for fertility control in the house mouse (Mus domesticus) using immunocontraceptive vaccines

Laboratory studies confirm the potential for fertility control in the house mouse Mus domesticus using mouse cytomegalovirus (MCMV) as a vector for an immunocontraceptive vaccine. This article presents an overview of key results from research in Australia on enclosed and field populations of mice and the associated epidemiology of MCMV. The virus is geographically widespread in Australia. It also persists in low population densities of mice, although if population densities are low for at least a year, transmission of the virus is sporadic until a population threshold of approximately 40 mice ha(-1) is reached. The serological prevalence of MCMV was high early in the breeding season of four field populations. Enclosure studies confirm that MCMV has minimal impact on the survival and breeding performance of mice and that it can be transmitted to most adults within 10-12 weeks. Other enclosure studies indicate that about two-thirds of females would need to be sterilized to provide effective control of the rate of growth of mouse populations. If this level is not maintained for 20-25 weeks after the commencement of breeding, the mouse population can compensate through increased recruitment per breeding female. The findings from this series of descriptive and manipulative population studies of mice support the contention that MCMV would be a good carrier for an immunocontraceptive vaccine required to sustain female sterility levels at or above 65%.

Pre-sowing control of house mice (Mus domesticus) using zinc phosphide: efficacy and potential non-target effects

Zinc phosphide was tested on populations of house mice in cereal stubble and pasture paddocks in the Central Mallee region of Victoria, in Autumn 1997. There were three replicates of two application methods: aerial and ground (perimeter) baiting. The response of mouse populations to baiting was monitored by live-trapping; estimates of population size and survivorship were compared between baited and unbaited sites (n = 3) taking prebaiting population sizes into account. Zinc phosphide was effective in decreasing the abundance (adjusted trap success) of mice on aerially baited sites (by 51%), but the reduction observed on ground-baited sites (24%) was not significant. There was no change in abundance on the untreated sites. There was a significant reduction in the survivorship of mice on both aerially and ground-baited sites compared with unbaited sites. Non-target species were monitored before and after baiting. Only four bird deaths were recorded as a result of the baiting program. Given that birds are highly mobile, with deaths possible many kilometres from the bait sitesit was difficult to fully assess the impact of poisoning on bird species in the area without more rigorous searching of vegetated areas further from baited paddocks.

The prevalence of viral antibodies during a large population fluctuation of house mice in Australia

We studied the seroprevalence of three viruses (mouse cytomegalovirus (MCMV), minute virus of mice (MVM), and mouse parvovirus (MPV)) in house mice (Mus domesticus) in 1995 7. In the first year average mouse density was less than 1 mouse/ha. From November 1995 to May 1996 the population increased at an average rate of 7% per week, a doubling time of about 10 weeks. From August 1996 to May 1997 the population increased at an average rate of 10% per week, a doubling time of about 7.5 weeks. From a peak around 250 mice/ha in May 1997, the mouse population fell 19% per week to 5 mice/ha in October 1997. The seroprevalence for all three viruses varied dramatically over time. MCMV had the highest seroprevalence (61.7%), followed by MVM (8.5%) and MPV (18.4%). Time series data indicated that MCMV spread rapidly through the population of mice once trap success was greater than 14% (40-100 mice/ha). By contrast MVM and MPV seroprevalence occurred with a 2-3 month and 3-4 month time lag, respectively. The current study supports the contention that MCMV would be a good carrier for an immunocontraceptive vaccine for controlling field populations of mice.