Vole Predators Research Articles

Numerical response of predators to large variations of grassland vole abundance and long-term community changes.

Voles can reach high densities with multiannual population fluctuations of large amplitude, and they are at the base of predator communities in Northern Eurasia and Northern America. This status places them at the heart of management conflicts wherein crop protection and health concerns are often raised against conservation issues. Here, a 20‐year survey describes the effects of large variations in grassland vole populations on the densities and the daily theoretical food intakes (TFI) of vole predators based on roadside counts. Our results show how the predator community responded to prey variations of large amplitude and how it reorganized with the increase in a dominant predator, here the red fox, which likely negatively impacted hare, European wildcat, and domestic cat populations. This population increase did not lead to an increase in the average number of predators present in the study area, suggesting compensations among resident species due to intraguild predation or competition. Large variations in vole predator number could be clearly attributed to the temporary increase in the populations of mobile birds of prey in response to grassland vole outbreaks. Our study provides empirical support for more timely and better focused actions in wildlife management and vole population control, and it supports an evidence‐based and constructive dialogue about management targets and options between all stakeholders of such socio‐ecosystems.

Killing time in cover crops? Artificial perches promote field use by raptors

AbstractCover crops are an increasingly common conservation practice in intensive row‐crop agriculture of the Midwestern United States and can improve wildlife habitat. However, they also benefit agricultural pest species such as voles (Microtus), which have damaged cover‐cropped soybean fields in Indiana. We tested the feasibility of attracting raptors, which are natural predators of voles, to cover‐cropped fields by supplying artificial perches from which to hunt. We assessed raptor use of artificial perches in cover‐cropped fields during the winters of 2018 and 2019. Perches were erected at three different distances from the field edge: 50, 125 and 200 m. We modelled perch use of our three most common species, great horned owl, red‐tailed hawk and American kestrel, with a logistic generalised linear mixed model. Raptors used 82% of the perches, and perch use was greatest at 200 m. However, even at peak use, our best model predicted a low probability of overall perch use for all three species. Artificial perches can attract raptors into large row‐crop fields. Sturdier perch design, extended perch availability and greater vole populations could increase use of perches. Although raptor perch use by itself is unlikely to control vole populations in cover‐cropped fields, artificial perches could form a valuable component of an integrated pest management system.

Predator-prey interactions in the canopy.

Small mammal abundances are frequently limited by resource availability, but predators can exert strong lethal (mortality) and nonlethal (e.g., nest abandonment) limitations. Artificially increasing resource availability for uncommon small mammals provides a unique opportunity to examine predator–prey interactions. We used remote cameras to monitor 168 nest platforms placed in the live tree canopy (n = 23 young forest stands), primarily for arboreal red tree voles (tree voles; Arborimus longicaudus), over 3 years (n = 15,510 monitoring‐weeks). Tree voles frequently built nests and were detected 37% of monitoring‐weeks, whereas flying squirrels (Glaucomys oregonensis) built nests infrequently but were detected 45% of monitoring‐weeks. Most nest predators were detected infrequently (<1% of monitoring‐weeks) and were positively correlated with tree vole presence. Weasels (Mustela spp.) were highly effective predators of tree voles (n = 8 mortalities; 10% of detections) compared to owls (n = 1), flying squirrels (n = 2), and Steller's jays (n = 1). Tree vole activity decreased from 84.1 (95% confidence interval [CI]: 56.2, 111.9) detections/week 1‐week prior to a weasel detection to 4.7 detections/week (95% CI: 1.7, 7.8) 1‐week postdetection and remained low for at least 12 weeks. Interpretations of predator–prey interactions were highly sensitive to how we binned continuously collected data and model results from our finest bin width were biologically counter‐intuitive. Average annual survival of female tree voles was consistent with a previous study (0.14; 95% CI: −0.04 [0.01], 0.32) and high compared to many terrestrial voles. The relative infrequency of weasel detections and inefficiency of other predators did not provide strong support for the hypothesis that predation per se limited populations. Rather, predation pressure, by reducing occupancy of already scarce nest sites through mortality and nest abandonment, may contribute to long‐term local instability of tree vole populations in young forests. Additional monitoring would be needed to assess this hypothesis.

Fluctuations in field vole abundance indirectly influence red grouse productivity via a shared predator guild

Changes in the abundance of one prey species may indirectly affect other prey species by triggering responses in generalist predators. Here we examine relationships between two prey species that do not compete directly, the field vole Microtus agrestis, a common rodent with fluctuating populations, and the red grouse Lagopus lagopus scotica, a gamebird inhabiting open moorland, during a 27-year study on a moor in south-west Scotland. First, we test whether vole abundance was related to grouse density and demographic rates. Second, we test whether vole abundance was related to abundance indices of four common predators of both voles and grouse (red fox Vulpes vulpes, weasel Mustela nivalis, hen harrier Circus cyaneus and common buzzard Buteo buteo). Third, we test whether these vole–grouse and vole–predator relationships differ in relation to grouse management, which includes the culling of foxes and weasels. We found no association between vole abundance and grouse densities, adult summer survival or nesting success. However, the ratio of young grouse per adult and the proportion of female grouse with broods in July were negatively associated with field vole abundance, suggesting increased predation of grouse chicks in years with high vole abundance. Fox indices showed a weak positive association with vole abundance when their numbers were not controlled, whilst weasel indices showed no relationship with voles. The numbers of breeding hen harriers and buzzards were also not associated with vole abundance, but the number of buzzard sightings was higher when voles were more plentiful. Our results are consistent with a negative interaction between field voles and red grouse chick survival in a pattern expected for apparent competition. Although the underlying mechanisms could not be disentangled, this interaction may be at least partly mediated by rodent-hunting raptors such as buzzards and, in periods without grouse management, foxes.

Trophic transfer of pesticides: The fine line between predator–prey regulation and pesticide–pest regulation

Abstract Understanding pesticide impacts on populations of target/non‐target species and communities is a challenge to applied ecology. When predators that otherwise regulate pest densities ingest prey contaminated with pesticides, this can suppress predator populations by secondary poisoning. It is, however, unknown how species relationships and protocols of treatments (e.g. anticoagulant rodenticide [AR]) interact to affect pest regulation. To tackle this issue, we modelled a heuristic non‐spatialized system including montane water voles, specialist vole predators (stoats, weasels) and a generalist predator (red fox) which consumes voles, mustelids and other prey. By carrying out a broad‐range sensitivity analysis on poorly known toxicological parameters, we explored the impact of five farmer functional responses (defined by both AR quantity and threshold vole density above which AR spreading is prohibited) on predator–prey interactions, AR transfer across the trophic chain and population effects. Spreading AR to maintain low vole densities suppressed mustelid and fox populations, leading to vole population dynamics being entirely regulated by AR use. Such vole‐suppression treatment regimes inhibited predation ecosystem services and promoted pesticide dependence. Keeping vole density below acceptable bounds by spreading AR while maintaining sufficient voles as prey resources led to less AR being applied and extended periods without AR in the environment, benefiting predators while avoiding episodes with high vole density. This may meet farm production interests while minimizing the impact on mustelid and fox populations and associated ecosystem processes. These alternating phases of mustelids and farmer regulation highlight the consequence of intraguild relationship where mustelids may rescue foxes from poisoning. Both global and wide‐range sensitivity analysis illustrate the tightrope between predator–prey regulation and pesticide–pest regulation. Synthesis and applications. Different pesticide protocols lead to a rich variety of predator–prey dynamics in agro‐ecosystems. Our model reveals the need to maintain refuges with sufficient non‐poisoned voles for sustaining specialist mustelids, to conserve the predator community given the potential of secondary poisoning with rodenticides. We suggest that long periods without pesticide treatment are essential to maintain predator populations, and that practices of pesticides use that attempt to permanently suppress a pest over a large scale are counterproductive.

Liver and fecal samples suggest differential exposure of red fox (Vulpes vulpes) to trans- and cis-bromadiolone in areas from France treated with plant protection products

Bromadiolone, a second generation anticoagulant rodenticide (SGARs), is authorized in France to control water voles (Arvicola scherman) outbreaks. SGARs enter the food chain and their persistence in rodents is responsible for secondary exposure or poisoning of predators and scavengers. Bromadiolone commercial formulations are a mixture of two diastereoisomers of bromadiolone: 70–90% is trans-bromadiolone and 10–30% is cis-bromadiolone. Both diastereoisomers were reported to inhibit coagulation function with similar potency. On the other hand, cis-bromadiolone has been shown to be less tissue-persistent than trans-bromadiolone in rats. Furthermore, cis-bromadiolone was not found in liver of red kites after bromadiolone poisonings of water voles.In this study, a multi-residue LC-MS/MS method for the quantification of the diastereoisomers of SGARs was used to investigate their proportions in field samples of another vole's predator, the red fox. Red fox livers (n=48) and scats (n=160) were collected in a pesticide use zone within a few months of bromadiolone application. We reported the concentrations of bromadiolone diastereoisomers in the livers and scats. Accumulation of bromadiolone was apparent in 81% (n=39) of the livers with mean and max concentrations of 355 and 2060ng/g, and in 23% of the faeces with mean and max concentrations of 78.5 and 593ng/g. However, cis-bromadiolone was not detected in the liver of 35 of 39 exposed red foxes and was present at very low concentrations (below 24.6ng/g) in 4 of 39 exposed red foxes. It was not detected in 11 of the positive scats and represented only 4.2% of the bromadiolone residues in scats. This demonstrated differential persistence of trans- and cis-bromadiolone in the food chain. The results suggest that a change of the proportions of bromadiolone diastereoisomers in baits could reduce the risk of secondary poisoning of predators, but retain primary toxicity for control water voles outbreaks.

Low recruitment not mortality limits growth of peripheral populations of Silene spaldingii

Populations at the periphery of a species range are thought to be less viable than those in the center because they are at the limit of their ecological tolerances. Plant population viability is determined primarily by mortality and recruitment, thus knowing differences in vital rates between central and peripheral populations is key to understanding range limits. Silene spaldingii S. Watson is a long-lived iteroparous plant that occurs throughout the eastern Columbia Plateau region of eastern Washington and adjacent Idaho and Oregon and is disjunct in northwest Montana. I recorded the fate of mapped S. spaldingii plants annually for 10 years in four populations, two from eastern Washington and two from Montana. Recruitment averaged three times higher and relatively constant at two central populations in Washington compared with two peripheral sites in Montana. Mortality was three times higher at one of the central populations compared with the remaining three sites due to vole predation. Vole activity was observed at the second central population but came too late in the study to be certain that it resulted in mortality. Vole predation was not observed in the peripheral populations. My results suggest that peripheral populations of S. spaldingii may only be able to persist as long as predation or other sources of mortality remain low and that intrinsic low and variable recruitment rates coupled with predation may help define the eastern range margin of this species.

Male and Female Meadow Voles, Microtus pennsylvanicus, Differ in Their Responses to Heterospecific/Conspecific Over‐Marks

AbstractVoles use runways, paths, and trails that may also be used by rabbits and mink. These shared areas could contain the scent marks of conspecifics and heterospecifics. Thus, it is likely that the scent marks of heterospecifics may overlap or be overlapped by those of voles, forming over‐marks. Much is known about how voles respond to over‐marks of two different conspecifics. However, we do not know how they would respond to an opposite‐sex conspecific whose scent marks are in an over‐mark with the scent marks of predator or the scent marks of a non‐predator heterospecifics. We tested the hypothesis that meadow voles, Microtus pennsylvanicus, differ in their response to the scent mark of the opposite‐sex conspecific if the scent mark was overlapped by that of a mink, a vole predator, or rabbit, a vole non‐predator. We found that female but not male voles showed a preference for the scent marks of the opposite‐sex conspecifics that were part of the mink‐vole over‐mark when compared to those of opposite‐sex conspecifics that were not part of the over‐mark. This preference by female voles was independent of whether the male vole was the top‐scent donor or bottom‐scent donor of the over‐mark. Male and female voles showed no preference between the scent marks of the opposite‐sex conspecifics whose marks were part of or not part of the rabbit‐vole over‐mark. Sex differences in the manner that meadow voles respond to rabbit‐vole and mink‐vole over‐marks are discussed.

Field vole (Microtus agrestis) seasonal spacing behavior: the effect of predation risk by mustelids

There are numerous studies showing that predation risk may change different aspects of the behavior of prey, such as habitat use, activity pattern, and foraging. Prey should exhibit the strongest antipredatory response against their most deadly predator. Small mustelids are considered the most important mammalian predators of voles. Nevertheless, there is no general agreement as to whether strong antipredatory reactions exist in natural free-living populations of voles. Here, we studied the field vole Microtus agrestis spatial reaction to high predation risk from small mustelids in the breeding (August) and nonbreeding (October) seasons under natural conditions. Voles were exposed to a caged weasel (Mustela nivalis) and a stoat (Mustela erminea), as well as to the odors of these predators. The reactions of 30 field voles were monitored with radiotelemetry. The field voles were found to display antipredator reactions that varied with season. In the breeding period, in response to predation risk, voles reduced locomotory activity and daily-range size, whereas in the nonbreeding period they did not. Changes in home range position were similar for control and treatment voles, in both the breeding and nonbreeding periods. The results indicate that mustelid predators modify the spatial behavior of small rodents in natural conditions depending on season. This might be a reflection of differences in state-dependent responses to predation from sexually active or inactive individuals. This suggests that the basic antipredatory reaction of voles under high predation risk from small mustelids limits their locomotory activity.

Barriers, Traps and Predators – An Integrated Approach to Avoid Vole Damage

Author(s): Fuelling, Olaf; Walther, Bernd; Nentwig, Wolfgang; Airoldi, Jean-Pierre | Abstract: Voles (Microtus spp. and Arvicola spp.) are the most abundant rodent species in open European landscapes. Due to their preference for agricultural habitats and their enormous reproductive potential, they are often regarded as pests. Several attempts have been made to reduce vole densities using rodenticide baits, gasses, or traps. No matter what method is used, they all bear the problem of voles reinvading from adjacent habitats. We tested a combination of fence and a new kind of trap that enabled terrestrial vole predators to take the captured prey. The combination of fence and traps was tested in a field trial and compared with mesh wire fences and an obstacle-free control line. This three-line setup was installed at each of three locations in Switzerland. Movement patterns of terrestrial predators were recorded by video observation during a 2-year period. Within this period, we made 1,224 observations of mammals; about ¾ of them, 951, were terrestrial predators and 157 were others like hares or hedgehogs. Due to their smaller size, only 116 voles were observed during the same time. Fences with traps were clearly preferred by predators, and their activity was significantly higher along fences with traps, as compared to the two other types. Predators seemed to check traps actively as they moved significantly more often close and parallel to fences with traps. Voles were not only removed from the traps but also caught while moving in the vicinity of the fences. The observed vole movements were ended by a predator in 11% of all instances. We found that barriers with additional trapping devices attracted predators, which started to patrol these fences regularly. Such a physical barrier in combination with its natural guard is a suitable device to protect high-value crops like orchards. As an integrated tool, it will reduce efforts, costs, and environmental impacts of vole control measures. Subsequent to this study, a new Hshaped double wall fence was constructed. This new type gives additional benefits, as it is easier to maintain and allows both terrestrial and avian predators to take captured voles.

Population dynamics in a cyclic environment: consequences of cyclic food abundance on tawny owl reproduction and survival

1. Understanding which factors regulate population dynamics may help us to understand how a population would respond to environmental change, and why some populations are declining. 2. In southern Finland, vole abundance shows a three-phased cycle of low, increase and decrease phases, but these have been fading out in recent years. During five such cycles (1981-1995), all tawny owls Strix aluco were censused in a 250-km(2) study area, and their reproduction and survival were monitored. 3. Males and females showed similar dynamics, but experienced breeders recruited more offspring and had higher survival than first breeders. Offspring recruitment, but not survival of breeding individuals varied in accordance with vole abundance. 4. The population's numerical response to prey abundance was primarily due to first-breeding individuals entering the population in the increase phase when immigration was the highest. First-breeding birds were younger, but experienced breeders were older in more favourable vole years. 5. A stage-specific matrix population model integrating survival and fecundity showed that, despite obvious variation in fecundity between vole cycle phases, this variation had limited importance for overall tawny owl population dynamics, but that the survival of experienced breeders during the low phase is most important for population growth. 6. Model and data agreed that the vole cycle drives the dynamics of this avian predator by limiting the recruitment of new breeders during the low phase. Population dynamics hence differ not only from the classic example of the species in a more temperate region in the UK where the number of territories is stable across years, but also from the dynamics of other avian vole predators in Fennoscandia where the recurring crash in vole abundance drastically lowers adult survival thereby creating vacancies.

Owl winter irruptions as an indicator of small mammal population cycles in the boreal forest of eastern North America

Contrary to what is observed in Fennoscandia, it seems to be widely accepted that small mammals do not exhibit multi‐annual population cycles in the boreal forest of North America. However, in the last thirty years, irruptions of vole predators such as owls have been reported by ornithologists south of the North American boreal forest. While such southerly irruptions have been associated in Fennoscandia with periods of low abundance of small mammals within their usual distribution range, their possible cyclic nature and their relationships to fluctuations in vole densities at northern latitudes has not yet been demonstrated in North America. With information collected from existing data‐bases, we examined the presence of cycles in small mammals and their main avian predators by using temporal autocorrelation analyses. Winter invasions of boreal owls (Aegolius funereus) were periodic, with a 4‐yr cycle in Québec. Populations of one species of small mammal, the red‐backed vole (Clethrionomys gapperi), fluctuated periodically in boreal forests of Québec (north to 48°N). Boreal owls show invasion cycles which correspond to years of low density of red‐backed voles, the main food item for this owl species. In addition, winter observations of northern hawk owls (Surnia ulula) and great gray owls (Strix nebulosa) south of their usual range increased in years of low density of red‐backed voles. Our results suggest that a 4‐yr population cycle exists in the eastern boreal forest of North America for voles and owls, which is very similar to the one observed in Fennoscandia.

Reproduction of the least weasel in captivity: basic observations and the influence of food availability

The least weaselMustela nivalis nivalis Linnaeus, 1766 is unique among carnivores because of its small body size and capacity for fast reproduction. It has been suggested to be the main agent for maintaining cyclic fluctuations in northern vole populations, largely based on its high reproductive potential and dependence on small rodents. This study describes basic reproductive data on the least weasel obtained during a captive breeding program. In the experiments, food availability was manipulated at the onset of breeding. Altogether, 65 litters were born during the 5-year study. The mean litter size was 5.1 (in 53 litters of known litter size), the most common litter size being six. The sex ratio of weaned young was not biased from 1∶1. The median date of birth was June 4. Food manipulations did not affect mating frequency suggesting that the observation of failure in breeding in years of low abundance of small mammals is due to mortality of embryos or young before weaning, but not due to avoidance of breeding at low food availability. In this respect, weasels differ from other main vole predators, owls and raptors, which often skip breeding if small mammals are scarce.

Do scent marks increase predation risk of microtine rodents?

Reproductive activities, including signalling with scents, may increase the risk of predation. Mammalian predators, like small mustelids, find voles by using odour cues of scent marks. Scent marks are also visible in ultraviolet light, and at least some diurnal raptors are attracted to these markings in the field. We performed a field experiment to find out whether manipulation of scent markings affects the density, survival and mobility of free‐living voles, and the activity of mammalian and avian predators. A total of 20 plots (each 1 ha) were randomly divided into two treatments: scent manipulation and control plots. Scent manipulation plots were treated with vole scent‐liquid and control plots with water. From each plot 1–2 voles were radio‐collared and tracked for three weeks. Predators hunted more often on scent manipulation plots than on control plots leading to lower survival time of voles. Although scent manipulation attracted more avian predators, small mustelids were the main predators of voles. The density or the mobility of voles did not differ significantly between manipulation and control plots. Our results suggest that odour of scent marks may be a larger risk to voles than UV visibility of scent marks.

Spatial synchrony in field vole Microtus agrestis abundance in a coniferous forest in northern England: the role of vole‐eating raptors

1. The regional synchrony hypothesis (RSH) states that synchrony in microtine abundance over large geographical areas is caused by nomadic avian predators that specialize on small mammals for food. This has proved a difficult hypothesis to test because experiments at an appropriate scale are almost impossible. 2. We used the decline of the most abundant, nomadic vole‐eating raptors in an extensive conifer forest in northern England (Kielder Forest) as a natural experiment to evaluate their influence on synchronizing voles at different spatial scales. Field vole populations fluctuated on a 3–4‐year cycle of abundance, similar to the periodicity in central Fennoscandia. 3. Over a 23‐year period, the combined numbers and density of kestrels and short‐eared owls significantly declined. If these raptors were responsible for synchronizing vole abundance, the decline should have been associated with a decrease in synchrony. We could find no change in synchrony during the period of the greatest decline in kestrel and short‐eared owl numbers (1980–97). 4. In Kielder, vole abundance has been shown to change in a wave‐like manner, with synchrony in the direction of the wave being 5–10‐fold smaller than that reported in Fennoscandia. Tawny owls are sedentary and the most abundant vole‐eating raptor in our study area, and might have an equalizing influence on vole abundance over smaller areas if they foraged in a density‐dependent manner and responded functionally to increasing vole density. If this was the case, spatial variability in vole density should have been less in occupied than unoccupied owl territories, especially in years of low vole density when owls could take a larger proportion of the standing crop of voles. Even though tawny owls caught a significant proportion of the vole population, we could find no difference in variation in vole density between owl territories that were unoccupied, occupied with no breeding attempt, or occupied with a successful breeding attempt. 5. We conclude that the small‐scale synchrony in field vole abundance is unlikely to be caused by avian predators. Instead, it is more likely to be related to the pattern of clear‐cutting that has developed in Kielder, which restricts vole dispersal. If this assumption is correct, we would predict more widespread synchrony in vole abundance in first‐generation forests when extensive areas are planted over short periods of time, and this is supported by anecdotal evidence. These conclusions indicate that foresters may be able to manipulate the spatial dynamics of voles and vole predators by varying patch sizes within forests.

Use of coupled oscillator models to understand synchrony and travelling waves in populations of the field vole Microtus agrestis in northern England

1. Earlier studies have reported that field vole Microtus agrestis populations in Kielder Forest, UK, exhibit typical 3–4‐year cyclical dynamics, and that the observed spatiotemporal patterns are consistent with a travelling wave in vole abundance moving along an axis south‐west–north‐east at approximately 19 km year–1. One property of this wave is that nearby populations fluctuate more synchronously than distant ones, with correlations falling lower than the average for the sampling area beyond approximately 13 km. 2. In this paper we present a series of models that investigate the possibility that both the observed degree of synchrony and the travelling wave can be explained as a simple consequence of linking a series of otherwise independently oscillating populations. Our ‘coupled oscillator’ models consider a series of populations, distributed either in a linear array or in a two‐dimensional regular matrix. Local population fluctuations, each with a 3–4‐year period, were generated using either a Ricker equation or a set of discrete‐time Lotka–Volterra equations. Movement among populations was simulated either by a fixed proportion of each population moving locally to their nearest neighbour populations, or the same proportion being distributed via a continuous geometric function (more distant populations receiving less). 3. For a variety of different ways of generating cycles and a number of different movement rules, local exchange between oscillating populations tended to generate synchrony domains that extended over a large number of populations. When the rates of exchange between local populations were relatively low, then permanent travelling waves emerged, especially after an initial invasion phase. There was a non‐linear relationship between the amount of dispersal and the domain of synchrony that this movement generated. Furthermore, the observed spatiotemporal patterns that emerged following an initial invasion phase were found to be highly dependent on the extreme distances reached by rare dispersers. 4. As populations of voles are predominantly distributed in grassland patches created by clear‐cutting of forest stands, we estimated the mean patch diameter and mean interpatch distance using a geographical information system (GIS) of the forest. Our simplified models suggest that if as much as 5–10% of each vole population dispersed a mean of 178 m between clear‐cuts per generation, then this would generate a synchrony domain and speed of wave in the region of 6–24 km (per year), which is reasonably consistent with the observed synchrony domain and speed. Much less dispersal would be capable of generating this scale of domain if some individuals occasionally moved beyond the nearest‐neighbour patch. 5. While we still do not know what causes the local oscillations, our models question the need to invoke additional factors to explain large‐scale synchrony and travelling waves beyond small‐scale dispersal and local density‐dependent feedback. Our work also suggests that the higher degrees of synchrony observed in Fennoscandian habitats compared with Kielder may be due in part to the relative ease of movement of voles in these former habitats. As our work confirms that the rates of exchange among local populations will have a strong influence on synchrony, then we anticipate that the spatiotemporal distribution of clear‐cuts will also have an important influence on the dynamics of predators of voles.

Does risk of predation by mammalian predators affect the spacing behaviour of rodents? Two large-scale experiments.

Predator-prey interactions between small mammals and their avian and mammalian predators have attracted much attention. However, large-scale field experiments examining small-mammal antipredatory responses under the risk of predation by mammals are rare. As recently pointed out, the scale of experiments may cause misleading results in studies of decision-making under predation risk. We studied the effect of small mustelid predators on the spacing behaviour of the gray-tailed vole (Microtus canicaudus) and the bank vole (Clethrionomys glareolus) in two separate field enclosure experiments. The experiments were conducted during the breeding season in North America and northern Europe, where small mustelids have been suggested to be important mammalian predators of voles. As in most of the earlier laboratory studies, predation risk was simulated using fresh mustelid faeces and urine. This made it possible to compare the results from experiments at different spatial scales. We did not find any effect of increased predation risk on spacing behaviour (mean and/or maximum distance moved and home range size) or trappability in either vole species. Simulated predation risk did not affect the breeding of females in gray-tailed voles, as has previously been shown in bank voles. The results disagree with most of the studies conducted in laboratory conditions with small mammals. We discuss whether this discrepancy could be caused by differences in the scale of the experiments.

Orchard Groundcover Management Systems Affect Meadow Vole Populations and Damage to Apple Trees

Meadow vole (Microtus pennsylvanicus Ord) populations, feeding activity and damage to young apple (Malus ×domestica Borkh.) trees were monitored for several years in a New York orchard by direct observation, trap counts, and a feeding activity index in various groundcover management systems (GMSs). Meadow vole population density differed among GMSs, with consistently higher densities and more trees damaged in crown vetch (Coronilla varia L.), hay-straw mulch, and red fescue (Festuca rubra L.) turfgrass tree-row strips. Vole densities were high in autumn and low in spring each year. Anticoagulant rodenticides and natural predation did not adequately control voles in GMSs providing favorable habitat. Groundcover biomass per m2 was weakly correlated with vole densities in 2 of 3 years, while the percentage of soil surface covered by vegetation was not significantly correlated with vole populations. Applications of thiram fungicide in white latex paint were better than no protection, but less effective than 40-cm-high plastic-mesh guards for preventing vole damage to tree trunks. A combination of late-autumn trapping, close and consistent mowing of the orchard floor, trunk protection with mesh guards, contiguous habitat for vole predators, and herbicide applications within the tree rows provided effective control of meadow-vole damage to trees at this orchard during 3 years without applications of rodenticide baits. Chemical names used: Tetramethylthiuram disulfide (thiram)

An estimate of the impact of predators on the British Field Vole Microtus agrestis population

AbstractThe productivity of the British Field Vole population is estimated to be between 677 000 and 982 000 voles per year, depending on the precise basis of the calculation. The total consumption of Field Voles by all the major predators, mammalian and avian, is estimated to be around 980 000, if the very uncertain consumption by Feral Cats is included. Two specialist vole predators (Weasel, Kestrel) and two generalist predators (Red Fox, Feral Cat) consume 85% of the total between them, the other 10 species share the rest between them. However important voles might be for owls, owl predation is unimportant to voles. The slight evidence for cyclicity in Field Vole populations in Britain might be explained by the overall take of voles by the predators, and by the rather generalized diet of even the vole specialists.

Orchard Groundcover Systems Affect Meadow Vole Populations and Damage to Apple Trees.

Meadow vole (Microtus pennsylvanicus L.) populations, feeding activity, and damage to young apple (Malus domestica Borkh.) trees were monitored by direct observation, trap counts, and a feeding activity index in different groundcover management systems (GMSs) for five years in a New York orchard. Vole populations differed greatly among GMSs, with consistently higher populations and more damage to tree trunks in crownvetch (Coronilla varia L.), hay-straw mulch, and red fescue (Festuca rubra L.)sodgrass GMSs. Vole populations were highest in the fall and lowest during the spring seasons each year. Anticoagulant rodenticides and natural predation did not result in adequate control of voles in GMSs that provided favorable habitat for nesting and feeding of this pest. The percent of soil surface vegetation coverage was not, but the amount of groundcover biomass was, a significant predictor of vole populations and damage to trees, independent of groundcover vegetation species. Trunk applications of thiram fungicide were less effective than 40-cm-high plastic mesh trunk guards, but better than no protective measures for controlling vole depredation in groundcover management systems (GMSs) with high rodent populations. A combination of late fall vole trapouts, close and consistent mowing of orchard floor vegetation, tree trunk protection with mesh guards, ample surrounding habitat for natural predators of voles, and suppression of tree row groundcover species with herbicides provided adequate control of meadow voles without the use of rodenticides at this orchard.