September 2013
Master Thesis Environmental Biology University Utrecht
Supervisor: dr. Pita Verweij
Index
Index...... 2 Summary ...... 3 Chapter 1: Introduction...... 4 1.1 The mammal as pest...... 4 1.2 The mole ...... 4 1.3 Research question ...... 6 Chapter 2: The influence of endogenous mechanisms on mole activity ...... 7 2.1 Circadian rhythm in moles ...... 7 2.1.1 The presence of neural structures ...... 8 2.1.2 Circadian rhythm in vitro...... 8 2.1.3 Circadian rhythm in vivo ...... 9 2.1.4 Conclusion...... 12 2.2 Mating behaviour in moles ...... 13 Chapter 3: The role of the environment on mole activity...... 15 3.1 Habitat preference revised...... 15 3.2 The influence of soil types and soil conditions on mole occurrence and activity...... 16 3.2.1 Habitat as driver of earthworms, and earthworms as driver of moles...... 17 3.2.2 Additional insights on the indirect influence of habitat on mole occurrence ...... 18 Chapter 4: Managing moles...... 20 4.1 Mole control nowadays...... 20 4.2 An appeal for Non-lethal methods ...... 22 4.3 Suggestions for future research ...... 23 Conclusions...... 25 References...... 27
2 Summary
Moles (Talpa europaea) largely go unnoticed as they live most of their lives in the subterranean. However, they are often perceived as a pest mammal because of their destructive digging activities. Shallow shafts and molehills may not only cause damage to aesthetics of gardens and golf courses, the heaps of dirt may also cause serious damage to agricultural equipment and crops. Fortunately, there are currently several methods available to control moles. The downside of these methods is that they are often found to be inhumane and the cost effectiveness is not always optimal. In order to control moles more effectively and use more animal friendly methods, it is important that more insight is gained in factors influencing activity. Therefore the main goal of this study is to assess how endogenous and exogenous mechanisms may influence mole activity and occurrence. The main findings are listed below:
• Circadian rhythm: There is evidence that under some circumstances, mole activity follows a 24h rhythm. Available literature shows that mole activity is not random or solemnly revolved around external cues. It is shown that during periods in which food is not limiting (i.e. spring and autumn), mole activity may be orderly arranged over a 24h cycle. However, when environmental changes occur, the cycle becomes quickly more distorted. It remains therefore questionable to what extent daily activity under natural conditions is dictated by this, apparently fragile, 24h cycle. • Mating season: Literature shows that mole activity during spring may increase as a consequence of male moles that go in search of receptive females. However, predictability of the increased activity remains uncertain on mole level; it is believed that individual male moles will increase digging activity only for several days at the most. To conclude, when combining the information on circadian rhythm and activity during mating season it appears reasonable to assume that mole activity (and thus soil disturbance) is more pronounced during spring compared to other seasons. • Habitat preference: Although moles are often believed to be rather indifferent to the habitat in which it occurs, recent research has shown otherwise. The available literature suggests that mole occurrence in arable fields is made possible by the quality of field margins. If field margins are somehow less suitable for moles, mole occurrence in arable field is reduced as well. • Food availability: It is shown that moles are indirectly susceptible for changes in habitat. Earthworms are relatively susceptible for changes in soil types and soil conditions. If for some reason soils become unsuitable for earthworms, or unsuitable for certain species of earthworms, mole occurrence and mole activity tends to diminish as well. Particularly effective appear to be acid soils and certain grass species that are little nutritious and degrade slowly.
The second goal of this study is to use the information gathered in the literature study to investigate the possibilities to improve effectiveness and increase animal-friendliness in mole control. Provided that more elaborate research is done, the findings in this study suggest that there are several non-lethal ways in which mole control can potentially be improved or cost effectiveness increased. For instance, trapping rate may increase if (live-) traps are set during periods when mole activity is generally higher (i.e. during spring). Also, literature suggests that manipulation of field margins may be a powerful tool in mole control in arable fields as it is both effective and easy manageable; desired effects may be realized by simply altering aspects of habitat such as grass species or acidity of soil.
3 Chapter 1: Introduction 1.1 The mammal as pest
When thinking of pests and diseases we mostly think of insects, viruses, fungi and bacteria. Other than rats maybe, it is often not realised is that there are also many mammal species that qualify as pests. An up-to-date overview in current trends in vertebrate pests within Europe comes from the 8th European Vertebrate Pest Management Conference (EVPMC) held in 2011. In the elaborate report of this conference it is shown that mammal pests are a worldwide problem, are often caused by rodents, and may form a threat in different ways and to different degrees. A large proportion of pest mammals found in Europe are classified as invasive species. The EVPMC report (editors: Jacob & Esther, 2011) shows that some invasive species are relatively harmless as they may only threaten local wildlife. Take for instance the American mink (Neovison vison), which hunts, since it’s introduction in Europe in 1930’s, mainly on riparian mammals. Some invasive species, such as the highly adaptable eastern grey squirrel (Scurius carolinensis), are considered more dangerous as they damage trees on large scale and may even pose a threat to the integrity of entire native ecosystems. Something similar seems to be the case for the invasive muskrat (Ondatra zibethicus) in Lithuania. Since it’s introduction in 1954 it has spread almost over entire Lithuania and its occurrence has a negative effect on amphibians, fish, molluscs, herbal plants, woody plants and coastal vegetation such as reed species. Other invasive vertebrate species are no true threat to local wildlife, or ecosystem functioning, but may threaten human safety instead. The coypu (Myocastor coypus) is increasingly found in German cities. There it not only attacks pets, but also attacks civilians. From the above it may appear that pest mammals are exclusively invasive species. That is not the case. The EVPMC report also shows several examples in which native mammal species are also seen as pests. As with some invasive species, damage caused by native species may be relatively harmless. The red deer (Cervus elaphus) for instance, is native to Europe, but as its distribution area increases it causes more and more damage to golf courses and urban areas. Other native mammal species are considered more detrimental as they may pose a serious threat to agricultural crops. Particularly notorious appears to be the common vole (Microtus arvalis). When there is an outbreak of this small rodent, it may cause significant damage to arable fields and forestry systems.
1.2 The mole
Only a selection of the wide variety of pest mammals, presented in the EVPMC report 2011, has been discussed in the above section. Yet it safe to say that mammals, like insects, may cause serious problems and can therefore with right be addressed as pests. Strangely one particular mammal seems to be lacking from the otherwise elaborate EVPMC report. Apart from a short notion on control measures in Scotland, nothing on Talpa europaena (the European mole) is mentioned. This seems strange as the European mole, although elusive, is often experienced as a pest. The European mole occurs almost through entire Europe. Its tolerance to a wide variety of habitats is impressive as well as notorious. The European mole is a small mammal with a rather peculiar appearance (figure 1). It has a cylindrical body, no external ears and its eyes are relatively small and covered by fur. Most notable are the front limbs,
4 which are well developed and skewed outward on both sides. As one may have guessed from the listed traits, moles are adapted to digging. They are fossorial animals that live their lives in almost complete darkness of the subterranean. They are mainly carnivorous and hunt for food (consisting of mainly of earthworms) through extensive tunnel systems. This makes moles almost intangible for potential predators such as birds of prey (i.e. owls, buzzards and ravens) or pets (i.e. cats and dogs), which are also known to occasionally catch moles (Sondergaard, 2006; Amori et al., 2008). The only moments when moles are truly exposed to predation is when young moles leave the nest, or at night when adult moles may leave their burrows to drink dew on leaves (Lund, 1976). The status of the mole is somewhat confusing. In some countries, such as Germany, moles are officially protected. In addition, in the context of biodiversity conservation, mole occurrence is often considered beneficial (Quy & Poole, 2004). Yet, in most countries moles are seen as a pest. In a survey held in Great Britain in 1992 it was shown that 97% of the farms had moles and in 64% of the cases farmers experienced them as a pest (Atkinson et al., 1994). Unlike many other pest animals the mole causes hardly any problems as a result of what it eats or hunts. As stated above, the mole mainly feeds on earthworms (or other insects). It is the way it hunts (and moves about) that is dreaded by gardeners, golf course owners and farmers alike. Although moles may make deep tunnel systems that go largely unnoticed, often they make shallow shafts close to soil surface or create molehills. Especially the latter of the two is considered detrimental as it may not only ruin the aesthetics of gardens, but may also cause serious damage to agricultural areas. As Lund (1976) already listed: (1) Molehills may reduce grazing area by up to 10%. Moreover, raised earth is not overgrown until three years after molehill formation. (2) Molehills may cause damage to agricultural equipment because of stones embedded in the raised earth. (3) Harvest may be polluted by sand and dirt from molehills. And (4) newly seeded plants are vulnerable disturbances and molehills may cause plant losses up to 25%. Exact figures on total damage caused by moles are scarce. One example comes from The Ministry of Agriculture, Fisheries and Food (MAFF), which made a rough estimation for Britain in the 1980’s. There it was found that annual cost to agriculture (which included the actual damage and control measures) was 2.9 million euro, which means that the mole is a relatively minor pest. However, if we look at a local scale one has to conclude that mole pests are often a persistent problem that is not easily dealt with. Especially in marginal areas where farmers are less fortunate, mole pests may have severe impacts on revenues (Gorman & Lamb, 1994). It is therefore a pest that should not be underestimated.
Figure 1. The mole (Talpa europaea). Source: wikipedia 5 1.3 Research question
Farmers are not powerless when moles infest their land. There are several mole control measures available that may reduce mole occurrence. However, it has to be concluded that many of the recommended measures are crude (i.e. inhumane), efficacy may fluctuate and cost-effectiveness remain questionable (Gorman & Lamb, 1994; Quy & Poole, 2004). In contrast what one might expect there is currently no clear overview available on mole activity. Therefore, the main goal of this study is to assess how endogenous and exogenous mechanisms may influence mole activity and occurrence. Although moles can be experienced as a pest mammal in various areas, the focus of this study will be on agriculture (i.e. arable fields). It is in this type of setting that mole pests are most serious and detrimental. The literature study is divided in several sub elements that are represented in different chapters. In chapter two, literature is discussed that provides information on endogenous mechanisms that may influence mole activity. In chapter three, literature is discussed that provides information on exogenous factors that may influence mole activity and occurrence. Ultimately, an answer to the main question will provide a more comprehensive picture on mole activity (and occurrence) Literature gathered in answering the main research question will automatically provide information for the second goal of this study, which is to investigate the possibilities to improve effectiveness and increase animal-friendliness in mole control. This will be further discussed in the fourth chapter. In the first part of the fourth chapter I will deal with current control measures. In the second part I will discuss the possibilities to incorporate the findings of chapter two and three to the palette of already used mole control measures.
6 Chapter 2: The influence of endogenous mechanisms on mole activity
In order to assess possible predictable patterns in molehill formation, chapter 2 will focus on the question how endogenous mediated signals may influence mole activity. First the influence of circadian rhythms on mole activity will be discussed. After that the influence of mating behaviour on mole activity will be discussed. Available literature shows that mole activity may show a 24h cycle. The only caveat of this cycle is that it appears to be very susceptible to environmental, seasonal and regional fluctuations. On the other hand, literature on mating behaviour indicates that especially male moles tend to display more (digging) activity during spring.
2.1 Circadian rhythm in moles
In many animal species activity is coordinated by endogenous neural rhythms. This ‘organic clock’ is not a static feature or absolute. In many animal species the internal clock is kept in sync by zeitgebers (which are external cues such as sunlight). If conditions are kept constant (for instance under lab conditions with constant darkness), the internal clock will start to ‘freerun’, resulting in an altered rhythm (Bertolucci et al. 1999). The dependence on zeitgebers and what is perceived as a zeitgeber differs between species. This essentially means that in different species the internal clock may have different cycle lengths and can be synchronised with different rhythms in the natural world. However, in (small) mammal species the internal clock revolves most commonly around a cycle of (more or less) 24 hours, which is also known as a circadian rhythm (Bartness & Albers, 2000). Especially in carnivores the biological clock is often found to follow a 24h rhythm. Presumably because carnivores depend on prey, which is a source of food that often has a distinct daily cycle with a limited availability or vulnerability (Zielinski, 1986). It has been suggested that activity in the mole (which is both a small mammal and carnivorous) would also follow a distinct 24h cycle. However, initial attempts during the thirties’ of the twentieth century to test this hypothesis neither confirmed nor denied the validity of this statement. First of all, these early studies pointed in different directions (some stated moles were more active during the day, others stated moles were more active during the night, others stated moles had a 4h rhythm rather than a 24h cycle). Secondly, research methods used in these studies were rather crude as they involved mostly indirect measurements such as registering tunnel openings. Ultimately no final conclusions could be drawn (Godfrey, 1955). Luckily, mole research didn’t stop during the thirties. In the years afterward and even quite recently studies have been published that give more insight on this particular matter.
7 2.1.1 The presence of neural structures One of the first questions that may arise when addressing the circadian rhythm in moles is to test whether or not moles have the ability to express endogenous mediated rhythms. Kudo et al. (1991) took an important step in unveiling the presence of an endogenous clock mechanism in moles (in this case Mogera kobeae). It was shown that most brain structures related to vision, such as visual nuclei in the dorsal thalamus and the midbrain, were underdeveloped. This was expected as these findings are in accordance to the subterranean lifestyle of moles in which, from an evolutionary perspective, eyes have become superfluous. Surprisingly not all vision related structures were found to be underdeveloped in moles in the study of Kudo et al. (1991). Parts of the central visual system, such as the suprachiasmatic nucleus of the hypothalamus (SCN) and retinohypothalamic projections were normally developed. Both systems play an important role in the endogenous clock mechanism. Therefore, this study shows that, while moles are virtually blind, visual structures that are of vital importance in regulating the circadian and circannual rhythms are still fully developed (Kudo et al., 1991).
2.1.2 Circadian rhythm in vitro Although the findings of Kudo et al. (1991) are interesting, it does not clarify if the found visual structures related to the circadian rhythm, are fully functional as such. Additional insights come from Bertolucci et al. (1999). In this study moles (Talpa romana) were captured and kept solitary in a controlled subterranean environment: temperature, humidity and food supply were kept constant. Subsequently, two different experiments were conducted. In the first experiment moles were exposed to a simulated natural day/night cycle. In the second experiment the day/night cycle as absent (i.e. moles were kept in total darkness). It was found that, in general, mole activity is characterized by several bouts of activity. These bouts may differ in their spatial arrangement during the day, but are comparable in terms of total frequency. Secondly, there seems to be a high level of individual differences between moles in terms of activity, which results in variable activity patterns even within a certain treatment. Thirdly, there are no signs of a true circadian cycle in moles that are kept under constant (dark) conditions; mole activity was disorderly and there was no sign of any form of cycle. And fourthly, it was found that when a day/night cycle was introduced, mole activity became suddenly more orderly arranged towards a clear and distinct diurnal activity (figure 2).
Figure 2. Diurnality index of Talpa romana over ten recording sessions. The closer the found results are to one, the higher expressed diurnality. LF1 = female mole 1, LM1 = male mole 1 and LM2 = male mole 2. Adapted from Bertolucci et al. (1999). 8 2.1.3 Circadian rhythm in vivo Bertolucci et al. (1999) have shown that is no clear circadian rhythm in moles under complete controlled conditions. However, when a natural occurring cycle was introduced (i.e. day/night cycle) mole behaviour became more predictable and orderly. So for a more conclusive answer on 24h rhythms in moles, there needs to be looked at in vivo studies. Godfrey (1955) analysed whether or not mole activity would show any predictable patterns during a 24h cycle under natural conditions. In this study, moles were labelled with a radioactive material and followed at a steady interval with a Geiger-Müller device. It was assumed that if mole activity were a function of endogenous rhythms, mole activity patterns in two very different environmental conditions would be comparable. Godfrey (1955) shows that there are some elements in the activity of moles that follow a predictable pattern during the course of a 24h cycle (table 1. ‘Comparable activity’). For instance, it is shown that in the Pasture plot there is a distinct resting peak around noon. Also, all studied moles seem to share in a similar pattern of rest and activity (which consists of 3 bouts of activity, alternated with 3 periods of rest). In addition, the total time spend on rest during a 24h period is roughly the same in the two varying habitats. However, Godfrey (1955) also notes that, while there are some similarities, there are many more inconsistencies in the activity of moles (table 1. ‘Different activity’). For instance, the found peak of rest around noon in the Pasture plot is not even remotely present in the Arable field plot. Additionally, the alternating units of rest and activity, while represented in all moles, differ greatly between the studied individuals and between the two habitats. Finally, Godfrey (1955) also assessed expected activity (in terms of rest, digging and moving) with observed activity. In this assessment it was assumed that there would be no difference in the activity pattern of moles in different habitats. However, activity was found to differ significantly (P=<0.001). In short, Godfrey (1955) seems to contradict Bertolucci et al. (1999), as it was concluded that there is no distinct 24h cycle under natural conditions.
9 Table 1. Summarized overview of highlights in Godfrey (1955) on the Activity of the mole during a 24-hour period. Activity of moles in the Pasture plot was predominantly recorded in April, while activity of moles in the Arable field plot was recorded in June and July.
Activity pattern of moles in Pasture vs. Arable field Activity (during 24 h period) Comparable activity Different activity Proportion of total activity spend Both in Pasture and in rest Arable field the total time spend on rest (hence activity) is roughly the same; 43% in Pasture vs. 46% in Arable field. Passive Units of rest 3 units of rest that The units differ in duration and period Rest alternate with 3 units of distribution. activity. Timing of rest In Pasture there is a peak of rest around noon, while in Arable field this peak is absent. Where does rest take place? In Pasture rest mainly takes place in nest, while in Arable field rest may also occur in tunnels. Proportion of total active period In Pasture 1/3 of active period is spend on continuous digging spend on continuous digging, while in Arable field 2/3 of active period is spend on continuous digging) Duration of a single outburst of Both in Pasture and continuous digging. Arable field 80% of a single continuous digging outburst was between 10 and 30 minutes. Focus of digging In Pasture moles tend to dig at several different places, while in Digging Arable field moles tend to focus their efforts on one spot in making additional tunnels. Active Shallow tunnel excavation Both in Pasture and period (i.e. formation of raised ridges on Arable field, the main soil surface) tunnel system was just below the soil surface. Deep tunnel excavation The digging of deep In Arable field the formation of (i.e. formation of molehills) tunnels took 13% in deep tunnels took in July a much Pasture and 15% in larger proportion of the moles total Arable field (in June) of continuous digging activity the moles’ total compared to June; Namely 56%. continuous digging activity.
Usage of tunnels In Pasture primarily the already existing tunnel-system was used, Moving while in Arable field new tunnels were constantly created and old tunnels were abandoned.
10 Additional insights come from MacDonald et al. (1996). As in Godfrey (1955) moles were studied in different habitats and different seasons. However, unlike Godfrey (1955) this was done more thoroughly as activity was recorded during spring, summer and autumn. This gives a more complete and less biased view on activity patterns. MacDonald et al. (1996) found that non-breeding moles (Talpa europaea) do tend to display a distinct rhythmicity during a 24h period that is characterized by three (eight- hour) bursts of activity. However the authors also state that the found rhythm is very dependent on seasonal changes: during spring and autumn the pattern is most clear, while during summer and winter the pattern becomes more disorderly (figure 3). MacDonald et al. (1996) state that the found differences in activity patterns are related to environmental changes during specific seasons. For instance, while earthworms are abundantly available in the upper soil layers during spring and autumn, this isn’t the case in summer. The authors argue that during summer soils dry. This will cause a reduction in worm biomass and will cause earthworms to migrate to deeper soil layers. Hence, less food is available for moles and thus their activity pattern changes. Interestingly, the found patterns in MacDonald et al. (1996) are comparable with Edwards et al. (1999), in which it is also shown that activity of moles is more pronounced during spring and autumn (figure 5).
Figure 3. Activity patterns of mole (Talpa europaea) in different seasons. Adapted from MacDonald et al. (1996) 11 2.1.4 Conclusion At first sight the discussed literature seems to conflict. After all, different studies point in different directions with respect to the presence of circadian rhythm in moles. Kudo et al. (1999) states the neural structures important in circadian rhythm are present. Bertolucci et al. (1999) show that under completely controlled conditions the proposed circadian rhythm is not present, but when a natural rhythm (day/light cycle) is introduced mole activity appears to become more orderly arranged. Additional insights come from in vivo studies such as Godfrey (1955) and MacDonald et al. (1996). These studies seem also in conflict as Godfrey (1955) concludes that there is no apparent circadian cycle in moles while MacDonald et al. (1996) states there is. On closer inspection the articles do not necessarily need to conflict. Assuming that the presented results are all correct, it can be concluded that mole activity is very variable and sensitive to external influences, as is shown in all the discussed articles. Also, when looking at all articles, it may be concluded that the variability is not something random and a 24h pattern appears to be present. The only problem is that the individual articles look at a too narrow scope to see the big picture. MacDonald et al. (1996) provides an overview, in which it is shown that activity in moles is strongly linked to seasonal changes. When environmental variables are at their optimum (i.e. when moles experience low levels of stress) a clear 24h pattern emerges. And when looking strictly at the presented results (and not considering the general conclusions of the individual articles), this finding is actually more or less confirmed in the other articles. Bertolucci et al. (1999) show that the introduction of a day/night cycle in an environment that is otherwise completely controlled (in which case it may be assumed the moles experience low levels of stress) will result in an orderly pattern. Godfrey (1955) shows that mole activity patterns may differ significantly over different habitats. However, if we look closely at the presented data (see table 1), it must be concluded that Godfrey didn't just look at differences in habitat. Namely, in Godfrey (1955) activity of moles in the pasture plot was recorded during April, and activity of moles in the Arable field plot was recorded during June and July. This means that activity of moles was respectively recorded in winter and spring. And as MacDonald et al. (1996) and Edwards et al. (1999) show, these are two periods in which differences in mole activity may already be expected. In other words, the differences in mole activity found in Godfrey (1955) may actually provide proof of what is also shown in MacDonald et al. (1996). The reasoning presented above is not yet studied in a more comprehensive study. So more research is preferably needed to substantiate this option. For now it may be assumed that there appears to be (some sort of) circadian rhythm in moles. However, this rhythm appears to be very susceptible for environmental variables and may easily disturbed. So from a more practical perspective it remains questionable how representative the proposed rhythm in moles is with respect to daily activity. Especially considering the fact that moles are often considered a pest in arable fields, which is a habitat that is anything from optimal (as will be shown in the next chapter).
12 2.2 Mating behaviour in moles
So far only circadian rhythms in moles have been discussed. Yet there is another possible endogenous driver of activity, namely mating behaviour. Technically speaking, mating behaviour in mammals can also be seen as product of the circadian rhythm (Goldman, 1999). But as mating behaviour in moles is confined to a season, it contrasts with the regular association that is commonly handled with circadian (which refers to a daily rhythm). Therefore, for clarity reasons, it was chosen to discuss mating behaviour in a different sub-chapter.
Gorman and Lamb In many animal species the mating season is a time of increased activity. Especially in small mammals it has been found that often females become more active (i.e. travel longer distances) when receptive for males (Daly 1978). So, maybe something similar that they move on. A number of mechanical devices are now commercially available, which, may be the case for molestheir manufacturers claim, perform. And if so, it may give the same task, but moreadditional insights in wefficiently. These scarershen to expect consist soil disturbances.of a probe that is pushed into the mole-infested ground, and which periodically transmits Unfortunately tvibrations of varyinghere is not much data availablefrequency depending upon the on matingmodel in question. behaviour If theyin moles and how it work, then affects activity. they would representSo, for any definite conclusions on this matter, more research is needed. a valuable, humane alternative to the use of poisons and traps. However, even with the limited sourcesThe aims of this work were to test the availefficacyable, some preliminary conclusions may be of three of these relatively expensive drawndevices. in expelling moles from the areas in which they are living. Lund (1976) states that moles are a highly territorial species in which even the sexes Background information live separately. Gorman and Lamb (1994) seem to confirm this phenomenon as can be seen Our in studiesfigure were4. carried This means out on wild, that free-living during mating moles. To season help the increased reader understand activity our may be expected,method as one of the two sexes of approach it is necessary toneedspresent to go in search of the other. According to Lund information on the general behaviour of the European mole, particularly concerning its social organization and patterns of activity. (1976) it are not the females (as is often the case in small mammals), but the males that will show increased activity durinMoles appear to enjoy a relativelyg a brief period in spring. simple and straightforward social order. For most of the year adults are solitary and sedentary creatures which occupy a mosaic of subterranean home ranges. The areas occupied by different individuals are largely exclusive and used by only one animal, although there is a small, varying degree of overlap between the ranges of some neighbours (Figure 1).
L--J30m o Males "Females
FigureFigure 4. Spatial distribution of moles (Talpa europea) in a pasture plot. Adapted from Gorman and Lamb (1994).1 A map of the home ranges of all the moles living in a pasture. The ranges are shown as the harmonic mean isopleth including 95% ofth:es. (after Gorman & Stone 1990)
The home range contains a complex network of semi-permanent tunnels which the mole regularly patrols, eating any soil-dwelling invertebrates, such as earthworms and insect larvae, that happen to be present when it passes (Gorman & Stone 1990). It is important to appreciate that most of a mole's food comes from what is present in these tunnels and that 13
4 Animal Welfare 1994, 3: 3-12 Edwards et al. (1999) provide an annual activity graph of moles (figure 5). Although Edwards et al. (1999) states that most fluctuations in mole activity are most likely related to variations in environment and food, the authors also state that the activity peak during spring may actually reflect mating behaviour of male moles, which is in accordance with Lund (1976). During summer, the new offspring will roam and set out to find their own territory. Once the have found a new area the young moles will dig their own tunnel system, hence the increased activity that is also observed during autumn. However, the degree of disturbance during autumn is highly dependable on the favourability of conditions during summer (Belmans, 2011). From this it appears reasonable to assume that (male) mole activity in spring increases as a consequence of mating behaviour. However, Lund (1976) also states that individual males will only increase their digging activity for one or two days. In addition, previous discussed studies constantly seem to point out that individual mole behaviour can be very variable and is difficult to predict. So, while increased activity is expected during spring in general, it remains highly unpredictable when specific males will increase their activity.
Figure 5. Seasonal patterns in molehill formation. Bars represent the number of molehills formed during a 3-month period in an area of 4608 m2. Adapted from Edwards et al. (1999).
14 Chapter 3: The role of the environment on mole activity
Chapter 3 will focus on the question how environmental variables may influence mole occurrence and activity in arable fields. First, habitat preference of moles is further analysed. Secondly, the influence of soil types and soil conditions on mole occurrence and activity is discussed. Available literature shows that arable fields are not amongst the preferred habitats of moles. Only when field margins are favourable, mole occurrence in arable fields is supported. Additional literature shows that for moles to occur in certain habitats, the soil needs to be able to support earthworm communities. If for some reason the soil becomes hostile for earthworms (when for instance pH is lowered), mole occurrence and activity tends to drop as well.
3.1 Habitat preference revised
According to the IUCN (Amori et al. 2008) the common mole (Talpa europaea) occurs in almost any area that has deep soil layers. As a result, moles may be found in a variety of habitats ranging from uncultivated areas (such as meadows and pastures) to cultivated areas (such as arable fields, gardens and parks). Only when soils are extremely sandy, stony or continuously waterlogged mole occurrence is reduced. From this it may appear that the mole is a very adaptable and robust species when it comes to suitable habitats. However, in a recent study of Zurawska-Seta and Barczak (2012) it is shown that habitat preference in moles (Talpa europaea) is more delicate than previously assumed. The authors state that in many animal species (vertebrates and invertebrates), occurrence in disturbed areas (such as arable fields) is facilitated by field margins. Field margins form the boundary between two habitat types and typically consist of linear patches of semi- natural vegetation. Because of the more complex structure of these margins, they provide various habitats and hideaways for various animal species that normally would not occur near arable fields. The authors argued that this might also be the case for moles. To test if field margins influence mole occurrence in arable fields, Zurawska-Seta and Barczak (2012) counted moles in three arable field plots with varying adjacent habitat types (i.e. different types of field margins). In doing so, the authors found that mole occurrence varied severely between the different types of field margins (figure 6). Field margins that formed the border between the arable plot and habitats with a relatively species rich vegetation, such as forests and roads that are characterized by broad species-rich shoulders (tarred road and broad ground road), harboured the highest amount of moles. On the other hand, field margins that formed the border between the arable plot and habitats with relatively scarce vegetation, such as adjacent arable fields or narrow ground roads, resulted in lower mole occurrence. The found results indicate, according to the authors, that mole occurrence in arable fields depends on field margin characteristics. If the field margins are broad and have a high diversity in terms of vegetation (i.e. wide areas of ecotones), moles are provided with shelter, nesting grounds and additional food sources. It is suggested that this way moles may endure seasonal activities in arable fields (such as chemical treatments and ploughing). If, however, field margins are narrow and anthropogenic in appearance
15 (when for instance the adjacent habitat is also an arable field), mole survival in arable fields becomes much more difficult. So, while moles may occur in arable fields, it is not their preferred habitat.
Figure 6. Mole occurrence in different types of field margins. Based on Zurawska-Seta and Barczak (2012).
3.2 The influence of soil types and soil conditions on mole occurrence and activity
In the previous paragraph it was shown that the assumption that moles are impassive to the habitat in which they may occur is not at all true. It appears that they are in fact rather selective. Zurawska-Seta and Barczak (2012) suggested that broad ecotones may be at the base of mole populations in a otherwise hostile environment, as they provide moles with an alternative habitat in which it may retreat and persist. Still, from Zurawska-Seta and Barczak (2012) it remains unclear what aspects of a habitat actually contributes to its suitability for moles. For instance, it remains unresolved why moles apparently prefer timber forests less then narrow ground roads or railway banks. Also, if we take a look at relative distribution of moles in different plots, it appears that the ‘popularity’ of certain similar types of habitat seems to vary. This in turn may suggest that moles have some specific habitat demands that are more refined than mere ecotone broadness.
One of the suggested explanations for the seemingly arbitrary variation in mole occurrence is their apparent susceptibility for variations within soil. As stated in the introduction of this chapter, moles tend to avoid certain soil types, such as muddy (water logged), stony or sandy soils. In addition, in several studies (such as in Milner & Ball, 1970 and Mellandby, 1966) it is shown that moles also tend to avoid specific soil conditions, such as soils with a low pH value. More recent studies support the statement that moles appear to be sensitive to certain types of soil and certain conditions of soil. In accordance with initial studies, Funmilayo (1977) shows that mole occurrence (abundance of Talpa europaea per hectare) and
16 activity (number of molehills per mole) may vary greatly between different habitats with varying soil types (figure 7: soil characteristics and mole occurrence). However, the results do not indicate that mole occurrence (or activity) in the two habitats is directly linked to variation in soil types. Instead, the results suggest an indirect link between soil types and mole occurrence.
Figure 7. Two different habitat types and the effects on Talpa europaea (abundance and activity) and earthworms (abundance and species composition). Based on Funmilayo (1977).
3.2.1 Habitat as driver of earthworms, and earthworms as driver of moles The collected soil samples in Funmilayo (1977) show that the two studied habitats (which were in close proximity of each other) are characterized by very different earthworm communities (figure 7: earthworm composition). First of all, the abundance of earthworms (expressed in biomass per m2) was found to be much lower in the sandy soil plot compared to the loam-sandy soil plot. The author suggests that inadequate food supply in the sandy soil may be at the base of the lower
17 earthworm occurrence. Especially the grass species Nardus stricta is stated to be an important contributor to the low supply of food in this specific plot: it is abundant, little nutritious and has a hard structure. This results in slow decomposition and eventually in high, but unavailable, levels of soil organic matter. Secondly, the earthworm species composition varies greatly between the two habitats. Interestingly, the author notes that species composition in plot A (the deep loam sandy soil) is characterised by burrowers and non-burrowers and species composition in plot B (the shallow sandy soil) consists exclusively out of burrowers. Taken together this suggests that local habitat characteristics greatly influence how many earthworms are actually supported in a certain environment and which earthworm species may occur. As can be seen in figure 7, mole occurrence is much higher in the Loam-sandy soil plot compared to the Sandy soil plot as there are more moles per hectare, more molehills per hectare and more molehills per mole. Hypothetically this may be caused by soil characteristics and/or earthworm composition. In other words, it remains unclear what exactly causes the difference in mole occurrence and activity. To get more insight in this last question Funmilayo (1977) performed a simple yet elegant test in which earthworm population density was compared between mole- infested areas and mole-free areas. It was found that earthworm population density was in all 8 tests higher in mole-infested areas compared to mole-free areas. Moreover, in 7 out of 8 tests the difference was found to be highly significant. This suggests that mole occurrence and activity is most likely determined by earthworm occurrence and species composition. Therefore this study provides evidence that mole occurrence and activity is directly influenced by earthworms and indirectly by habitat characteristics.
3.2.2 Additional insights on the indirect influence of habitat on mole occurrence Funmilayo (1977) has shown that mole occurrence is highly dependent on earthworm occurrence and that earthworm occurrence is in turn dependent on local soil variables. However, what the author failed to assess is the influence of individual elements of soil and environment on earthworms (and eventually on mole occurrence). Edwards et al. (1999) takes the next step by assessing how earthworm occurrence (expressed in Area m2 of earthworm casts) and how mole occurrence (expressed in number of molehills per plot) is affected by varying individual conditions. The results are shown in figure 8 and lead to two conclusions. First of all, the results show that earthworms appear to be less susceptible to chemicals, as earthworm occurrence remained unaffected when soil was treated with chemicals such as insecticides and molluscicides. On the other hand, the results also show that earthworms appear to be highly susceptible to certain environmental changes, such as shifts in vegetation and liming of relatively acid soils. Secondly, as in Funmilayo (1977), there appears to be a correlation between earthworm occurrence and mole occurrence. Visually speaking, when looking at figure 8, molehill formation seems almost in perfect tandem with earthworm occurrence. The authors confirm the causal link by stating that when the area of earthworm casts is used as a covariate, the effects of liming and grass removal (herbicides) on molehill formation becomes non-significant. This implies that the change in molehill formation in these treatments can directly be linked to changes in earthworm abundance (which could also be seen as an extra confirmation of the causal link between earthworm occurrence and moles found in Funmilayo, 1977).
18
Figure 8. The effect of several treatments on mean number of molehills and earthworm casts. *P<0,05, **P 19 Chapter 4: Managing moles Chapter 4 will focus on the question which mole control measures are used nowadays, and what role the presented results (in chapter 2 and 3) may play in future mole control measures. 4.1 Mole control nowadays As stated in paragraph 1.2, moles are considered only a minor pest from a national perspective. However, as is also noted in paragraph 1.2, mole pests may be a persistent problem on a local scale that is both costly and difficult to manage. Strangely, if we are to believe ads on Internet and local newspapers, unwanted molehills are a problem of the past. Especially widespread are the devices with a vibrating probe, which are supposed to scare moles away by emitting vibrations through the soil. However, Gorman and Lamb (1994) have already shown that these types of solutions are rather ineffective to repel moles. Although the tested mole repelling devices did in fact produce vibrations that were send into the ground, there were no apparent effects on mole behaviour. The authors found that the emitted vibrations attenuated quickly and were undetectable after a few meters. In addition, the studied moles appeared rather indifferent to the devices even when they were within range of the vibrations. So, what does help to reduce mole occurrence and molehill formation? A possible answer comes from the Department of Environment Food and Rural Affairs (Defra), which presented a report on mole control in 2004 (editors: Quy & Poole, 2004). In this report current (i.e. what is used in 2004) practices and techniques with respect to mole control are discussed. In table 2 the most important findings concerning efficacy, applicability and humaneness of the different mole control approaches have been summarized. One of the findings is that extensive data on any of the discussed control approaches are lacking and far from ideal. Most information is anecdotal, which makes it difficult to assess efficacy of control measures in general and how it will perform on a large-scale. Despite these limitations, the authors were nonetheless able to show that the most feasible way to currently deal with moles includes lethal measures (see table 2). Poison baits, fumigants and especially kill-traps are widespread and have shown to be effective. Of these options, the authors show that, theoretically, strychnine used in poison baits is most cost-effective measure. However, there are several caveats (other than limited available data) to consider in the financial assessment done by Quy and Poole (2004). For instance, strychnine, while effective, is nowadays officially banned within the EU as a means to eradicate moles (Clover, 2007). Also the humaneness of kill-traps is questionable and for that reason change in legislation may be at hand (Quy & Poole, 2004). In addition, when the cost- effectiveness of the top 3 measures was assessed by Quy & Poole (2004), various cost- pressing proceedings were not taken into account: Traps may be re-used or cheaply imported, knowledge and experience of operators may enhance efficacy of the alternative treatments, and a pre-treatment assessment may substantially reduce wastage of fumigants (Quy & Poole, 2004). 20 Table 2. Mole control techniques and methods within the European Union. Based on Quy & Poole (2004) Description Characteristics Country BE DK FR DE NL UK Efficacy Applicability Humaneness Earthworms are treated Adequate application - Difficult to apply, as earthworms need Lethal measure. X (strychnine is banned) X (strychnine is banned)) with poison (typically may result in 75% mole to be individually collected. - Lethal dose (which means the consumption of 2- strychnine hydrochloride) reduction in a matter - Host may die before it reaches mole. 3 poisoned earthworms) takes up to 15 minutes and released. of days. - Often treatment is ineffective as moles to kill mole. clean the earthworms before eating, - If only one poisoned worm is eaten it may not n baits which means that retreatment is needed kill mole, but result in sickness (full recovery after - Controversial method: strychnine is 48 hours) banned since 2006. Poiso Phosphine gas (aluminium Varying results, which - Reported higher material costs Lethal measure. X X X X X X phosphide) is injected in soil may vary between 30- compared to strychnine (poison baits) - Adequate dose of 130 ppm takes up to 30 100% mole reduction treatment, while it has no higher efficacy minutes to kill mole - Considered labour intensive, as - However, if dose is inadequate moles may suffer application needs to be highly accurate. for three to four days before dying Essentially this means that pre-treatment visits are needed to assess active runs (i.e. where moles are present). Fumigants - If previous step is not done accordingly, efficacy of treatment may be reduced. Traps are set in the tunnel If traps are operated by - Moles are sensitive to soil (and tunnel) Lethal measure (kill-trap). X X X (to a lesser extent) X (to a lesser extent) X system: experienced personnel, disturbances. Therefore, all or nothing - Humaneness of kill-traps remains questionable. - In the case of live traps a mole reduction of approach required for maximum efficacy. The traps may cause instant death, but there are moles are captured when 70% may be expected If set traps are insufficient with respect numerous examples that show that moles may the mechanism is triggered. to the amount of moles present, the initially survive, in which case they suffer - In the case of kill-traps traps may be by-passed or completely unnecessarily for a prolonged period. moles are killed when the removed from soil by moles. mechanism is triggered. The - To maximize efficiency even more, Non-lethal measure (live-trap). most commonly used kill- similar treatment on adjacent fields is - Humaneness of live-traps is still not fully Trapping traps nowadays are the required as well. understood. It may appear humane as moles scissor trap and half-barrel - Considered only feasible on small scale survive the traps and are released in designated trap. (such as private gardens) areas. However, it is yet unknown if the released moles are able to survive as these areas are most likely already inhabited by territorial conspecifics. - Physical repellents: the - Scientifically - Although most ‘repellents’ are relatively Non-lethal measure. X X placement of sharp objects supported repellents: cheap and easy to apply (such as - There is not much known about humaneness or in the tunnel system. 1. Experimental trials mothballs), their efficacy is not damage that the commercial repellents may - Auditory/ vibrating with natural predator scientifically supported. And in the case cause to moles. repellents: the placement of odours and mole of physical repellents, moles may easily - One may assume that repelled moles will sound generating/ vibrating perpetual gland remove or by-pass the sharp objects. migrate to adjacent fields. It is yet unknown if the devices in ‘infected’ field. secretions (regardless - Predator odours and mole secretions migrating moles are able to survive in the - Olfactory repellents: the of gender) were found may work, but the relative costs and adjacent fields, as these areas are most likely placement of odorous to be effective labour intensiveness are considered too already inhabited by territorial conspecifics. substances in tunnel system. 2. Commercial high to form a feasible alternative Repellents repellents such as - Extensive information on commercial Renardine (UK) and repellents remains scarce. From what is calcium carbide known, it can only be applied effectively repellent gas on small scales and short-term regime (1 (Germany), may month). actively repel moles Fences are placed around - No data available on - System mainly used in Germany to keep Non-lethal measure. X pasture at 100 cm depth in efficacy, but given the moles out of pasture after repelling soil to block moles. fact that moles may dig them. deeper than one meter - Fencing costs are high and efficacy it may assumed that unclear. Fences the system is not impeccable. Habitat is manipulated to - Varying results - Habitat manipulation can already be Non-lethal measure. X X repel and reduce local ranging from minimal achieved by planting certain plant species -There is not much known about humaneness. earthworm population. As to severe reduction in (such as Euphorbia spp. or Nardus stricta) Most forms of habitat manipulation appear rather earthworms are the main mole occurrence. or alter the soil pH by adding Nitrogen harmless. However, some studies show that using food source of moles, this - Data derived from (lowering soil pH) or to keep soil pH low pesticides may also effectively reduce earthworm will result in lower mole experiments (no (i.e. by not liming). abundance. This more aggressive approach may occurrence. information on actual - Some forms of habitat manipulation have more severe implications. application). may interfere with crop revenues Earthworms (excessive nitrogen application). 21 4.2 An appeal for Non-lethal methods As can be seen in table 2, also non-lethal methods in mole control are taken into account in the Defra report (Quy & Poole, 2004). However, the authors reasoned that these options are currently not feasible as they were found to be either ineffective in mole control, not cost-effective or there was simply not enough conclusive evidence (i.e. lack of data sets) available to put one of the non-lethal approaches forward as a viable alternative. At the time of writing, the Defra report is about 10 years old. Many of the objections will therefore still stand as not many new revelations have been added to the pool of articles cited in the Defra report. Nonetheless there are several arguments available that should be considered as well. First of all, the authors have (unintentionally) deprived readers any form of critical reflection on the presented facts, as no actual data (in the form of graphs or tables) of the cited studies have been included. Although there is no question that the general conclusions are solidly founded, some valuable aspects presented in several cited studies have this way been discarded or dismissed too easily. For instance, elaborate studies on earthworm-habitat dynamics, such as of Funmilayo (1977) and Edwards et al. (1999), are only shortly discussed and important findings remain unnamed. As can be seen in chapter 2 these articles provide valuable information on the effect of habitat alteration on earthworm abundance and species composition. In addition both studies provide strong evidence that mole occurrence and activity is linked to earthworm abundance and composition. So, although one has to agree that the pool of articles supporting mole control through earthworm control is limited, the firmness and nature of the found results in the cited articles cannot simply be ignored or dismissed. Secondly, the need for alternatives to lethal control measures grows. Legislation with respect to lethal mole control methods may change rapidly. Already strychnine has been banned, and as awareness grows on inhumanness of kill-traps, changes in that sector may be nearby as well (Quy & Poole, 2004, Clover, 2007). Even when kill-traps are continued to be allowed, there may be problems down the road. As Quy & Poole, (2004) state, the cost-effectiveness of the remaining lethal methods (kill-traps and fumigants) is questionable. It is even suggested that, with strychnine banned, it may be more feasible to do nothing than control moles at all. Thirdly, although there are not many new publications since the Defra report, there are some interesting developments. First of all, as can be seen in chapter 2 there is growing evidence suggesting that mole activity may follow a distinct 24h hour pattern. Especially during spring, when the rhythm is most pronounced and falls together with the mating season, increased activity may be expected. It stands to reason that (live-) traps set during this period will be more effective compared to other seasons. In addition, as can be seen in chapter 3, there is some new evidence available supports a habitat manipulation approach in mole control. Take for instance the article of Zurawska-Seta and Barczak (2012). This study clearly shows that mole occurrence in arable fields is to a great extent dependent on field margin conditions. The results suggest that if field margins are somehow unsuitable for moles, mole occurrence in arable fields is no longer supported. This in turn may have severe implications on how mole pests in arable fields (or similar areas) should be controlled. Instead of controlling mole populations across the entire field, which is both time consuming and not very cost-effective, controlling habitat conditions at field margins may prove to be sufficient enough as well. On top of 22 that, by controlling moles through field margins a possible downside of successful earthworm control (namely that earthworms may provide important ecological services) can be minimized as only small strips of land are treated. Finally, in a recently published study on the Iberian mole (Talpa occidentalis), a mole species that is endemic to the Iberian Peninsula, some interesting similarities with Talpa europaea were found. Hierro et al. (2012) show that, as with the European mole, the Iberian mole tends to occur at much higher numbers when the soil is suitable for high numbers of earthworms (i.e. when soils are moist, soft or covered with herbs). Thereby the authors provide additional proof for the suggested close relationship between habitat characteristics, earthworms and moles. 4.3 Suggestions for future research There appear to be some promising options available for non-lethal mole control measures. However, even with the additional literature there are some gaps in knowledge that remain unresolved. Therefore, more research needed before non-lethal measures may be successfully applied on large-scale. It is important that this research is done as it may result in a more efficient, more cost-effective, and a more animal-friendly approach to mole control. To make this more concrete, several of the most pressing gaps in knowledge are listed below: • Cost-effectiveness of mole control: This should be seen as a more general remark that applies to all future research. Mole pests are often local. Although this may seem like an advantage from a control perspective, in reality it is not. Practically it means that costs of control measures are an ever-present limiting factor for less fortunate farmers (Gorman & Lamb, 1994, Quy & Poole, 2004). If suggested measures are simply too expensive (regardless their efficacy), it is unlikely that these measures are adopted. • Efficacy of earthworm control: There is a lack of knowledge on potential efficacy of earthworm control in mole-infested areas. Current studies have only been able to show that there appears to be a link between earthworm abundance and mole occurrence and activity. Yet, the full potential (or commercial applicability) remains unexplored. • Detrimental effects of earthworm control on soil conditions and local biodiversity: The influence of earthworm control on environment (including detrimental effects on soil) has not yet been fully mapped, especially in context of mole control. It is not only important to assess the risks of earthworm control on the environment, but also to look at possibilities to strike a balance between benefits (mole control) and costs (possible negative impact to soil, productivity and biodiversity). A possible hint towards a solution may already be provided Funmilayo (1977). As can be seen in figure 7, not only earthworm abundance differs in different habitats, also the composition of earthworm species is altered. So far, there has been no research done to the effects of different earthworm species on mole occurrence. Hypothetically speaking there could be a win-win situation if moles are found to be less attracted to certain species of earthworms. This way, moles may be controlled with only minimal consequences to soil. • Animal-friendliness of life-trapping: Another gap in knowledge can be found in trapping. Efficacy of this measure stands or falls with timing. If the traps are not set adequately the first time, there is a chance moles may start to avoid them or even 23 remove them from their tunnel system (Quy & Poole, 2004). As stated in the previous paragraph, given the fact that mole activity does tend to display a certain pattern, it stands to reason that this may be used in mole control. However, currently there is no literature available on how knowledge on activity patterns in moles may contribute to the efficacy of trapping. In addition, as already stated in Quy & Poole (2004), it remains unknown if released moles from live-traps will survive in their new environment. The areas in which the trapped moles are introduced are often already be occupied by other (territorial) moles. Therefore, to get more insight in humaneness of live-traps, more research is needed. • Use of field margins: Research should be done to the possibilities to use field margins in mole control. Recent research by Zurawska-Seta and Barczak (2012) has shown that field margins may play an important role in mole occurrence in arable fields. The implications of this finding, as explained in the above paragraph, are promising and may potentially imply a radical change in mole control. However, since the study of Zurawska-Seta and Barczak (2012) is still the only study that shows the importance of field margins, the first step would be to do additional research on the importance of field margins on mole occurrence. In a later stage there can be looked at how habitat manipulation or live-traps within these margins may contribute to mole control. 24 Conclusions Although moles are often considered only a minor pest from a national perspective, on a local scale they may cause serious damage and are often difficult to manage. Therefore, the study served two main purposes. The first goal was to assess how endogenous and exogenous mechanisms may influence mole activity and occurrence. The second goal was to use the information gathered in addressing the first goal to investigate the possibilities to improve effectiveness and increase animal-friendliness in mole control. With respect to the first goal, several conclusions may be drawn. As can be seen in chapter 2 internal mediated rhythms, such as a circadian rhythm and mating behaviour, may dictate mole activity to a certain extent. The actual influence of these mechanisms on the resultant activity remains questionable as the circadian rhythm appears very susceptible to external cues and the mating behaviour in males will last only short (a matter of days). On the other hand, during spring the circadian rhythm appears most pronounced (and most reliable) and mating behaviour is also confined to this season. This suggests that during spring, mole activity may be expected to be more elevated compared to other seasons, and thus increased soil disturbance may be expected as well. Chapter 3 shows that mole activity is highly dependent on external variables. Available literature shows that this is presumably because of the moles’ dependence on earthworms. It is shown that relatively minor changes in soil are enough to alter earthworm abundance and composition. In turn, mole occurrence follows the earthworm fluctuations almost in tandem. Interestingly increased earthworm abundance will not only increase mole occurrence, but also its activity, as molehills per mole tend to increase as well. The literature discussed in chapter 2 and 3 enable us to better understand mole activity and therefore provide information for the second goal of this study. In chapter 4 it was shown that many of the used measures in mole control management are considered costly and inhumane. Take for instance Strychnine. This was considered to be the only true efficient way in controlling moles, yet is has recently been banned. In short, there is a need for alternatives to control mole pests more effectively and animal-friendly. Some of the insights presented in chapter 2 and 3 may prove to be useful in future non-lethal mole control measures. For instance, setting (live-) traps during spring may be more effective as mole activity tends to be more pronounced as well. In addition, habitat manipulation may result in lower earthworm abundance, which in turn results in lower mole occurrence. Most notable is the recent discovery that mole occurrence in arable fields appears to be made possible by field margins. When these margins are unsuitable for moles, their abundance is found to be substantially lower within arable fields. Unfortunately, in chapter 4 it is also shown that current information on the more promising non-lethal approaches is too anecdotal or lacking in extensive datasets. Therefore, additional research is needed before non-lethal approaches can be applied successfully on large-scale. First of all, future research should include more elaborate studies on earthworm/mole dynamics and cost-effectiveness of this approach. It is currently unknown how effective earthworm control is in a situation where moles are considered a pest. Similarly it is not yet known if earthworm control will lead to other soil related problems such as nutrient deficiency or a shortage in aeration (etc.). On the other hand, there is also not much known if certain assemblies of earthworm species are less preferred by moles. If so, a win-win scenario may be possible in which moles are 25 repelled and soil retains its structure. Secondly, there should be looked at humanness of live-traps as the released moles are currently placed in areas already occupied by other (territorial) moles. There is not much known about the wellbeing of these newly introduced moles. Thirdly, future research should explore more elaborately how field margins affect mole occurrence in arable fields and how these margins may be incorporated in future mole control. And finally, future research should also take into account that rural farmers may have limited financial means to control moles. Cost- effectiveness of suggested measurements should therefore always be given priority. 26 References Amori, G., Hutterer, R., Mitsain, G., Yigit, N., Kryštufek, B. & Palomo, L.J. 2008. Talpa europaea. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.1. 27