Exploring patterns of female house mouse spatial organisation among outbreaking and stable populations

The size and distribution of home ranges reflect how individuals within a population use, defend, and share space and resources, and may thus be an important predictor of population-level dynamics. Eruptive species, such as the house mouse in Australian grain-growing regions, are an ideal species in which to investigate variations in space use and home range overlap between stable and outbreaking populations. In this study, we use spatially explicit capture-recapture models to explore if space use and home range overlap among female mice could serve as indicators of changes in population density leading into summer. Additionally, we assess the sensitivity of space use and home range estimates to reduced recapture rates. Our analysis did not reveal variations in the spring spatial organisation of female mice based on existing capture-mark-recapture data. However, our study highlights the need to balance monitoring efforts within regions, emphasising the importance of exploring studies that can improve spatial recaptures by optimising trapping efforts. This is particularly important in Australian agricultural systems, where varying farm management practices may drive differences in population dynamics.

Spatial and Temporal Dynamics of Contact Zones Between Chromosomal Races of House Mice, Mus musculus domesticus, on Madeira Island

Analysis of contact zones between parapatric chromosomal races can help our understanding of chromosomal divergence and its influence on the speciation process. Monitoring the position and any movement of contact zones can allow particular insights. This study investigates the present (2012-2014) and past (1998-2002) distribution of two parapatric house mouse chromosomal races-PEDC (Estreito da Calheta) and PADC (Achadas da Cruz)-on Madeira Island, aiming to identify changes in the location and width of their contact. We also extended the 1998-2002 sampling area into the range of another chromosomal race-PLDB (Lugar de Baixo). Clinal analysis indicates no major geographic alterations in the distribution and chromosomal characteristics of the PEDC and PADC races but exhibited a significant shift in position of the Rb (7.15) fusion, resulting in the narrowing of the contact zone over a 10+ year period. We discuss how this long-lasting contact zone highlights the role of landscape on mouse movements, in turn influencing the chromosomal characteristics of populations. The expansion of the sampling area revealed new chromosomal features in the north and a new contact zone in the southern range involving the PEDC and PLDB races. We discuss how different interacting mechanisms (landscape resistance, behaviour, chromosomal incompatibilities, meiotic drive) may help to explain the pattern of chromosomal variation at these contacts between chromosomal races.

Rat-bites of an epidemic proportion in Peshawar vale; a GIS based approach in risk assessment

Contemporary studies demonstrate that rodent bites do not occur frequently. However, a huge number of cases were reported from Peshawar vale, Pakistan during 2016. Two species, the local black rat Rattus rattus (Linnaeus, 1758) and the invasive brown rat Rattus norvegicus (Berkenhout, 1769) might be the suspected cause. Several studies indicated the invasion of brown rats into Pakistan presumably via port city of Karachi. In this study, we modeled geospatial distribution of rodent bites for risk assessment in the region. Bite cases reported to tertiary care lady reading hospital were monitored from January 1 to August 31, 2016. Among 1747 cases, statistically informative data (n = 1295) was used for analyses. MaxEnt algorithm was employed for geospatial modeling, taking into account various environmental variables (temperature, precipitation, humidity, and elevation) and anthropogenic factors (human population density, distance from roads, distance from water channels, and land use/land cover). MaxEnt results revealed that urban slums (84.5%) are at highest risk followed by croplands (10.9%) and shrublands (2.7%). Anthropogenic factors affecting incidence of rodent bites included host density (contribution: 34.7), distance from water channels (3.2), land use/land cover (2.8), and distance from roads (2). Most of the cases occurred within a radius of 0.3 km from roads and 5 km from water channels. Rodent bite incidence is currently at its peak in Peshawar vale. Factors significantly affecting rodents' bite activity and their distribution and dispersal include urbanization, distance from roads, and water channels. Further studies are needed to determine the impact of invasion by brown rat on bite incidence.

Ecology and management of rodents in no-till agriculture in Washington, USA

No-till farming is an important approach to sustainable agriculture because it can conserve soil and water resources. Unfortunately, rodent populations can thrive under no-till conditions because burrow systems are not disrupted by annual plowing and plant residues build-up on the surface, providing cover and insulation. This can result in substantial crop damage. We assessed rodent populations, habitat use, food habits, and crop damage in a no-till cropping system in Washington, USA. We also conducted preliminary trials of methods to reduce rodent populations and crop damage. In the fall, many more rodents were captured in fields with unharvested crops than in fields containing only plant stubble, suggesting that rodents leave fields after crop harvest, providing that suitable habitats are nearby, even when adequate cover is still available in harvested crop fields. By spring, the number of voles captured was much lower relative to fall. Despite this, capture rates were much higher in surrounding permanent grass areas than in crop (barley, wheat, pea) fields, suggesting that these grassy areas serve as refugia for rodents. Furthermore, the permanent grass cover type was the landscape variable most associated with rodent capture rates. In three winter pea fields, rodents removed 5-15% of the pea plants over winter. Examination of stomach contents revealed that voles mainly fed on grain plants in spring, but that their diet was more diversified in fall. Deer mice fed heavily on grain plants in both spring and fall, but also used insects as food. Metal barrier exclosures (9 m × 9 m), extending above and below ground, did not prevent access by rodents. Rodent populations in areas treated with zinc phosphide on grain were comparable to untreated areas 1 year after application of the rodenticide, perhaps because of immigration and recruitment, suggesting that baiting does not provide a long-term solution to rodent damage in no-till agricultural fields.

Can rodent outbreaks be driven by major climatic events? Evidence from cyclone Nargis in the Ayeyawady Delta, Myanmar

BACKGROUND

Massive rodent population outbreaks occurred in the Ayeyarwady Delta, Myanmar, in July 2009, 15 months after cyclone Nargis. Satellite imagery with high temporal frequency was used to identify the area and planting time of rice at a landscape scale of > 80 000 ha, and household surveys of farmers were conducted to validate the mapping and to quantify losses.

RESULTS

Farmers did not have problems with rodents in 2007-2008; rodents were the principal problem in the 2009 summer and monsoon rice crops. The landscape scale modeling indicated that high rodent densities in 2009 were associated with extended or delayed cropping and harvesting time because of asynchronous planting, and with an increase in the amount of abandoned agricultural land after cyclone Nargis.

CONCLUSION

Asynchronous planting following cyclone Nargis provided abundant high-quality food for an extended period, which in turn led to a lengthened breeding season of rodents. The outbreak of populations 15 months after cyclone Nargis is consistent with the time it would take rodent populations to build from a low base after a major flooding event. To prevent rodent outbreaks effectively, synchronous planting, use of rice varieties with a similar maturation date and good field sanitation are important actions for subsequent rice crops after a major weather event.

Response of small rodents to manipulations of vegetation height in agro-ecosystems

Some small mammal populations require human interference to conserve rare or threatened species or to minimize adverse effects in plant production. Without a thorough understanding about how small rodents behave in their environment and consideration of how they react to management efforts, management will not be optimal. Social behavior, spatial and temporal activity patterns, predator avoidance and other behavioral responses can affect pest rodent management. Some of these behavioral patterns and their causes have been well studied. However, their impact on pest rodent management, especially for novel management approaches, is not always clear. Habitat manipulation occurs necessarily through land use and intentionally to reduce shelter and food availability and to increase predation pressure on rodents. Rodents often respond to decreased vegetation height with reduced movements and increased risk sensitivity in their feeding behavior. This seems to result mainly from an elevated perceived predation risk. Behavioral responses may lessen the efficacy of the management because the desired effects of predators might be mediated. It remains largely unknown to what extent such responses can compensate at the population level for the expected consequences of habitat manipulation and how population size and crop damage are affected. It is advantageous to understand how target and non-target species react to habitat manipulation to maximize the management effects by appropriate techniques, timing and spatial scale without causing unwanted effects at the system level.

Comparison of population estimators and indices for monitoring house mice in sorghum crops

House mice (Mus musculus domesticus Schwarz & Schwarz, 1943) are monitored in Australia and China to track changes in mouse population densities and forecast their potential damage to cereal crops. The present study compared population indices based on the number of different mice caught and overall trap success from live-trapping with an oil card index (OC) and a tracking index (T) for monitoring mice in sorghum crops immediately before crop maturation. T was measured as the percentage of track board covered with mouse footprints night(-1), and OC as the percentage of card removed by mice night(-1). The reliability of these abundance indices was quantified by Pearson correlation coefficient with the trappable population size (Ñ), which was estimated by capture-recapture over eight consecutive nights on 175 × 5 trapping grids, in sorghum crops on two properties on the Darling Downs, Queensland. Because of differences among individual mice in capture probability, Model M(h) of program MARK was used to account for such heterogeneity and to estimate the size of each mouse population. The number of individual animals caught was more strongly correlated with Ñ than trap success and, therefore, might be a more reliable index; the data suggest that three trapping occasions provide optimal precision for this index. T correlated significantly with Ñ only at sites where the canopy of sorghum plants was closed, and its use should, therefore, be restricted to this habitat. OC did not correlate with Ñ because none or very little of the cards was eaten at low to moderate mouse densities. T and the number of animals caught over three trapping nights are recommended for monitoring mice in sorghum crops immediately prior to crop maturation.

Managing crop damage caused by house mice (Mus domesticus) in Australia

A large-scale outbreak of the house mouse populations occurs in grain growing in Australia on average once every four years. High densities of mice cause major yield losses to cereal crops, and low to moderate densities of mice also cause some losses. Several predictive models based on rainfall patterns have been developed to forecast mouse density. These models carry some uncertainty and the economic value of basing management actions on these models is not clear. Baiting is the most commonly used method and zinc phosphide and other rodenticide bait are effective in reducing up to 90% of mouse populations. Ecologically-based best farming practice for controlling mice has recently been developed on the basis of long-term field studies of mouse populations. No effective biological control method has been developed for mice. However, grain growers still cannot make economically rational decisions to implement control because they do not know the pest threshold density (D(T)) above which the economic benefits of control exceed the economic costs of control. Applied predator-prey theory suggests that understanding the relationship between mouse density and damage is the basis for determining D(T). Understanding this relationship is the first research priority for managing mouse damage. The other research priority is to develop a reliable method to estimate unbiased mouse density.

Does the house mouse self-regulate its density in maturing sorghum and wheat crops?

1. One of the central questions in population ecology and management is: what regulates population growth? House mouse Mus domesticus L. populations erupt occasionally in grain-growing regions in Australia. This study aimed to determine whether mouse populations are self-regulated in maturing sorghum and wheat crops. This was assessed by examining food supply to mice (i.e. yield) and the relationship between initial mouse density (D(I)) and density at harvest (D(H)). Eight levels of D(I) ranging from 89 to 5555 mice ha(-1) were introduced to sorghum at the hard dough stage and to wheat crops at the milky stage in mouse-proofed pens. D(H) was measured by trapping out mice 49 days after the introduction. 2. There were at least 3.11 tonnes ha(-1) of wheat and 1.85 tonnes ha(-1) of sorghum grain available for mice at harvest. The estimated relationship between D(I) and D(H) was asymptotic exponential, with D(H) initially increasing almost linearly with D(I). When D(I) was above c. 500 mice ha(-1), D(H) increased asymptotically with D(I) and then saturated at c. 3100 mice ha(-1). The asymptotic increases in and saturation of D(H) was due partly to more young mice being born and recruited in pens treated with lower levels of D(I). 3. Our findings indicated that mouse densities in maturing cereal crops were driven by a numerical response of mice to the abundant supply of grain, modified by some unknown self-regulation mechanism that reduced this numerical response of mice at higher mouse densities. The mechanism was possibly spacing behaviours. Although the nature of this self-regulation mechanism is not known our model is, nevertheless, useful for predicting increases and eruptions in mouse population density in sorghum and wheat crops. Understanding the nature of this mechanism may provide insights into population processes that can be exploited in controlling mice in cereal crops.

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.

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.

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.

Microgeographical distribution of two chromosomal races of house mice in Tunisia: pattern and origin of habitat partitioning

Two chromosomal races of the house mouse occur in Tunisia, a standard morph (40St) found all over the country, and a derived morph (22Rb) occurring only in central Tunisia. In this region, habitat partitioning between the two morphs was investigated by a microgeographical analysis of their distribution, assessing habitat characteristics and demographic parameters. Results showed that the 22Rb mice always occurred in the oldest sections of towns (medinas), often extending to more recent surrounding neighbourhoods where the 40St morph was most abundant. The latter was never trapped within the medinas. The transition between the two morphs was located within cities in the more recent areas, the hybrid zone being estimated at less than 0.5 km in width by a clinal analysis of chromosomal data. Although differences between habitats exist, almost no demographic differences were found between populations of the two morphs when they occurred in the same or in different habitats. Two hypotheses are discussed to account for the origin of habitat partitioning. The first relies on competitive exclusion of the 40St mice from the medinas by the derived 22Rb mice; the second is based on stochastic processes related to historical evolution of Tunisian urban communities.

Effects of landscape type and extensive management on use of motorway roadsides by small mammals

We compared the relative abundances of small mammals along extensively managed motorway roadsides (with a narrow mown strip adjacent to the roadway) in three distinct landscapes (garrigue, pine plantation, and intensive farmland), to evaluate the relative effects of management and landscape traversed on roadside small-mammal populations. In each landscape, the landscape matrix (adjacent habitats), the mown strip, and the intervening unmown strip of roadside were sampled using snap traps. The roadside communities differed from those of landscape matrices, both in the relative abundances of individual species and in the proportion of each species captured. Species richness was greater on roadsides than in cropland and pine plantations, but there was no difference in the garrigue landscape. However, this greater richness was due to species that were rarely caught. The three dominant species (93.7% of captures), greater white-toothed shrew (Crocidura russula), wood mouse (Apodemus sylvaticus), and common vole (Microtus arvalis), were generally more abundant on roadsides than in the landscape matrices, especially in the unmown strip in the case of the first two species. Voles showed seasonal variation, being more abundant in mown strips at the population peak. The ecotone attributes of extensively managed motorway roadsides seem to be favourable to most small-mammal species, regardless of the landscape matrix.