Introduction

The European hare (Lepus europaeus) is an important game species in Europe. Since the 1960s, the number of European hares throughout Europe has been declining, also in Switzerland. The European hare is classified as threatened on the Swiss Red List (Duelli 1994). For that reason, the hare abundances in 56 study sites have been determined annually in the Swiss Hare Monitoring since the year 1991 (Jenny and Zellweger-Fischer 2011). During the Europe-wide decline phase, many studies have been conducted to analyse habitat selection of European hares to be able to improve the suitability of the habitat for this species (see Supplementary material for an overview). Some habitat types are consistently reported in the literature to be avoided by the European hare, e.g. residential areas (Roedenbeck and Voser 2008; Vidus-Rosin et al. 2009), or preferred by it, e.g. fallow land (Smith et al. 2004; Bertolino et al. 2011a, b). However, evidence of use of most other habitat types from different studies is contradictory in part. As an example, woodland and hedges are reported to be avoided in some studies (Tapper and Barnes 1986; Roedenbeck and Voser 2008; Ferretti et al. 2010; Cardarelli et al. 2011; Bertolino et al. 2011b) and preferred in others (Tapper and Barnes 1986; Homolka et al. 1988; Bertolino et al. 2011a).

One reason why some habitat types are contentiously discussed in the literature might be that there are differences in habitat classification in the various studies. Detailed habitat type mapping is costly and the additional effort has to be compensated by producing valuable information. It is open to question how detailed a habitat classification has to be in order to represent European hares’ habitat preferences satisfactorily. Moreover, some habitat categories may be more prone to change their importance for European hares than others, if they are pooled into broader categories. It is therefore important to know which habitat categories have to be mapped in more detail than others to record European hares’ habitat preferences.

Habitat selection in this lagomorph species is known to be affected by hare density (Jezierski 1973; Pépin 1986). However, all studies on habitat selection have been conducted in areas where European hare densities are between medium and high as densities range between 15 to 74 animals per 100 ha (Pielowski 1966; Jezierski 1968; Pépin 1986; Tapper and Barnes 1986; Marboutin and Aebischer 1996; Smith et al. 2004, 2005; Pépin and Angibault 2007; Vidus-Rosin et al. 2009, 2011; Ferretti et al. 2010; Cardarelli et al. 2011; Bertolino et al. 2011b). Finding habitat preferences at high densities is difficult as most available habitats are occupied (Frylestam 1979) due to intraspecific competition for resources and the use of unpreferred habitats by subordinate individuals. Therefore, European hares’ habitat preference or avoidance in areas with high densities may differ from those in areas with low densities.

In addition, all detailed studies on habitat preferences were conducted in agricultural areas where mean field sizes range from 7 to 20 ha (Pépin 1986; Marboutin and Aebischer 1996; Smith et al. 2004, 2005; Pépin and Angibault 2007). Thus, certain habitat types such as fallow land or hedges, which are often reported to be preferred by hares, might be either clumped or rare. This may influence European hares’ habitat selection and effectuate different results for habitat preferences of hares living in agricultural areas with small field sizes compared to those with medium to large field sizes.

Moreover, European hares’ home ranges include resting areas used during the day and feeding areas frequented at night (Averianov et al. 2003), although during summer, the species’ active period is not restricted to the dark phase (Holley 2001; Schai-Braun et al. 2012). Studies analysing day and night habitat preferences separately confirmed that habitat preferences differ widely depending on the European hares’ activity state (Tapper and Barnes 1986; Smith et al. 2004; Cardarelli et al. 2011; Bertolino et al. 2011b). The European hares’ feeding areas consist normally of open grounds with short vegetation (Tapper and Barnes 1986), whereas resting areas are comprised of structured landscapes providing shelter (Tapper and Barnes 1986; Neumann et al. 2011). One study has shown that European hares selected their habitat with reference to vegetation height, and their preference depended on whether they were foraging or resting, as well as on the time of the year (Smith et al. 2004). It is therefore questionable whether the vegetation height is one factor explaining the European hares’ habitat preference.

The objective of this study was to evaluate habitat preferences of European hares in spring and autumn during the activity period, in the early hours of the night, in an agricultural area with low hare density and small field sizes. In particular, we focused on the question whether two different habitat classifications varying in their specificity might cause contradictory results regarding European hares’ habitat preferences. Moreover, we hypothesised that the European hares’ preference or avoidance for the habitat types in agricultural land during the active period can be explained by vegetation height.

Material and methods

Study area

The study was conducted in Northern Switzerland in the canton of Basel-Landschaft near Wenslingen (47°26′ N, 7°54′ E) and consisted of 989 ha of farmland composed of 32 % arable crops with cereals as the main crop, 50 % grassland, 4 % forest, 1 % permanent culture, 1 % unfarmed area and 11 % rural development (including buildings, gardens, etc.). The study area comprised of farmland including small villages surrounded by a forest belt. The forest belt, although not surveyed, was included in the study area in further analyses, since European hares recorded at the forest edge might use the forest as habitat (see data collection below). Field size was typical for Northern Switzerland and averaged 0.66 ha (±0.01 SE) ranging from small plots with a minimum of 0.003 ha to large fields with a maximum of 12.17 ha. We measured vegetation height on every field in the agricultural land by the drop disc method (Holmes 1974) to the nearest 5 cm. Excluded were tree-covered habitat types, hedge, thickets and rivulets, as their height could not be quantified accordingly. We measured homogeneous vegetation at a random point of the field, whereas for heterogeneous vegetation, where the vegetation tended to be at two different heights, we recorded the minimum and maximum vegetation heights and afterwards calculated the mean. Plants’ dormancy is a period of arrested plant growth which enables for example plants to survive winter in our climate. Plants’ dormant season in the study area starts in October and ends at the end of March/early April corresponding with the occurrence of temperatures below 0 °C (Federal Office of Meteorology and Climatology MeteoSwiss).

Hare density at the study site was estimated each year in autumn and spring by spotlight counts (Langbein et al. 1999) and accounted on average 5.7 European hares per 100 ha (±0.18 SE) during the study period (Zellweger-Fischer 2010). Hare numbers remained stable along the 3 years of the study. As the study site is remotely located, there is little disturbance by leisure activities, such as horse riding, jogging or dog walking, and 47 % of the road surface area is not tarred.

Data collection

From autumn 2007 until spring 2010, European hares were counted twice both in late March/early April and in November. Spotlight counts were done in the agricultural land on roads from a car driving at a speed of 15–20 km per hour. The forest belt and the residential areas were excluded from the spotlight count transect as European hares are reported to use open fields during the activity period (Tapper and Barnes 1986). Spotlight counts for each hare survey were done on two nights per season along four transects of total 61.48-km length by the local hunters. Thereby, the complete agricultural land of the study area (915 ha) was illuminated during each spotlight count. The position of each European hare was mapped and later digitised with the software ArcGIS 9.1 (ESRI). In the same months of the hare surveys, the landscape composition and agricultural use were recorded and digitised. Thereby, a different map of land use was created for each hare survey by taking a ground-truthed land register map as basis. If the land use of a parcel, the minimum unit mapped, was not consistent, the boundaries within the parcel were determined by using a handheld GPS device. The land use was mapped as accurately as possible for the season. This resulted in a classification comprising of 29 habitat types (Tables 1 and 2). A rough classification containing five categories pooled all the 29 study site’s habitat types into broader groups. The classifications of the habitat types were the same for each hare survey. Around each point where a European hare was mapped, a circle with the size of 25 ha was drawn. We chose 25-ha circles since small home-range sizes of European hares in agricultural landscapes are recorded to be around 25 ha (see for an overview Smith et al. 2004). We assumed that our study animals had small home ranges because average field size seems to influence the European hares’ home-range size and our study area’s average field size was small. Only European hare points whose circle area was located at least 75 % within the study area were used for further analyses. Subsequently, the landscape composition within the circle was evaluated assuming that the habitat types within the circle were actually being used by the individual hare. For every 100 ha of the study area, eight random points were selected per season and year. Since no data on hare presence were collected in the forest and residential areas, all random points within these two habitat types were discarded to avoid bias. The same procedure as used for the European hare points was applied to the random points. This resulted in a total of 601 random points and 612 European hare positions used for analysis. Note that we performed the same analysis with a larger assumed home range (50-ha circles), but the results did not differ.

Table 1 The 29 habitat types used to classify the study site’s land use with the vegetation height (in centimetre), a rough classification into five categories and their area covered in percent
Full size table
Table 2 Plant species characteristic for the species-rich pasture and unimproved grassland
Full size table

In different parts of an area, an unequal visibility of hares may be caused by structures, e.g. hedges in the landscape (Pegel 1986; Roedenbeck and Voser 2008). Such unequal visibility would result in a non-random distribution of the hares missed during the spotlight counts. Nevertheless, we assume this to be negligible in our study since structured habitat types such as set-aside, tree nursery, dwarf orchard, gardens, allotments, graveyards and vegetable fields comprised only 3.7 % of the study area’s landscape (Table 1) and as few as 5.6 % of all fields had a hedge.

Data analysis

The European hares’ habitat preferences were measured by using Chesson’s electivity index ε (Chesson 1983), an index based on Manly’s alpha (Manly et al. 1972) which can be used to analyse habitat preferences (Krebs 1989), among others. We chose Chesson’s electivity index, because it has the advantage that results between cases for which the number of available habitat types vary are comparable. The Chesson’s electivity index ranges between −1 and +1, with negative values showing a negative selection, whereas positive values signify a positive selection. If the index value is zero, the habitat type concerned is used in the same proportion as it is available. We calculated on the one hand the Chesson’s electivity indices for each of the 29 habitat types and on the other hand for each habitat type of the rough categorisation. The reliability of the electivity indices was tested using the bootstrap method (Dixon 1993). The original ε i values (ε i = Chesson’s electivity index for the habitat type i) were resampled 1,000 times with replacement, and an accelerated bootstrap confidence interval was calculated (Fig. 1). The accelerated bootstrap adjusted the confidence interval for bias and skewness (Efron and Tibshirani 1993). If the two values of the lower and upper boundary featured the same algebraic sign, the selection for this habitat type was significant. All analyses were done with the software R 2.12.0 (R Development Core Team 2011).

Fig. 1
figure 1figure 1

Chesson’s electivity indices and their distributions of 1,000 bootstrap resamples (medians with 25th/75th and 10th/90th percentiles) for all habitat types based on the analysis of a spring and b autumn. The habitat types of the rough categorisation are indicated by grey shading. Not significant results are marked with the abbreviation n.s. See text for details on statistics

Full size image

Results

Rough categorisation of all habitat types

A rough classification of all the study site’s habitat types into broader groups showed that both in spring and autumn, the European hares avoided urban areas, unfarmed areas and grassland, whereas for agricultural crop land, this species displayed no significant preference (Fig. 1). Moreover, the animals preferred tree-covered habitats in spring, while in autumn, there was no significant selection for this habitat type recordable. Except for urban areas, the variability in European hare preferences within each of the rough categories was considerable.

The 29 different habitat types

In tree-covered habitats, European hares displayed avoidance of forest and dwarf orchards both in spring and autumn. Compared to this, tree nurseries were not significantly selected. We found that in spring and autumn, hares had a high preference for grubbed acres but avoided winter oilseed rape and winter grain. The species positively selected germinating seeds and showed no significant selection for the other habitat types within the category agricultural crop land in spring. In contrast, ploughed acre, intertillage, vegetables and stubble fields were preferred and harrowed acre and germinating seed were avoided by the animals in autumn. Note that grain legumes were not available in autumn. In both seasons, our results showed a significant avoidance of all types of grassland except species-rich pasture, which was highly preferred. When looking at the different types of unfarmed areas separately, the European hares expressed in spring and autumn a preference for rivulets and field margins. In contrast, hedges, thickets and set-asides were avoided. Besides, the hares preferred fallow land in spring but expressed no significant preference for the same habitat type in autumn. European hares avoided residential areas and gardens, allotments and graveyards both in spring and autumn. Furthermore, hares negatively selected all types of roads.

Vegetation height of the habitat types in the agricultural land

The vegetation height of 5,226 fields recorded in the agricultural land during the three study years was on average 15 cm (±5.9 SE) high with a minimum of 0 cm and a maximum of 200 cm. Only in the category unfarmed areas did the measured vegetation heights vary substantially between the different habitat types (Table 1).

Discussion

Rough categorisation of all habitat types

The rough categorisation of all habitat types into broader groups revealed a negative selection by the European hares for the unfarmed and urban areas in spring and autumn. That urban areas are avoided by active European hares has been suggested by different studies (Roedenbeck and Voser 2008; Vidus-Rosin et al. 2009). The avoidance of unfarmed areas is, however, more difficult to interpret. The reason for this might be that different kinds of habitat types with variable vegetation structures were pooled into this one category. European hares showed an electivity index around zero or no selection at all for the other three categories. Our results imply that it is most important to differentiate between the studied habitat types in relation to vegetation height, cover, composition, etc. and to avoid the pooling of habitat types differing in these premises in order to avoid losing information. Hence, for some categories, e.g. grassland or agricultural crop land, where selection varied widely, more detail might be needed as for others, such as urban areas, where all subcategories were systematically avoided. The pooling of habitat types might therefore be responsible for the controversially discussed habitat types such as grassland and pastures in the literature about active European hares’ habitat preferences (Frylestam 1980; Barnes et al. 1983; Tapper and Barnes 1986; Smith et al. 2004; Cardarelli et al. 2011; Bertolino et al. 2011b).

The 29 different habitat types

Tree-covered habitat types

European hares in spring and autumn negatively selected forests and dwarf orchards but expressed no significant selection for tree nurseries. All three habitat types are unfavourable for hares during the activity period with respect to the vegetation structure which inhibits an open view. However, hares might use tree nurseries as feeding grounds during the plants’ dormant season. In another European hare study, mostly needles of coniferous trees and shoots of trees and shrubs were found in the stomach during winter when availability of herbage is impaired (Homolka 1982). Dwarf orchards in the study area are protected against large herbivores by wire fences. This might also impede smaller herbivores from using dwarf orchards as feeding grounds because the access to the trees is restricted and, therefore, make this habitat type less accessible for European hares.

Agricultural crop land

European hares in spring and autumn expressed a strong preference for grubbed acres. Grubbed acres still offer a fraction of the dug-over field crop or grassland at the field surface which might be used in the plants’ dormant season by the European hares as a food source. Winter grain and oilseed rape were negatively selected in spring and autumn by European hares. Freshly grown winter grain is reported to be a widely used food source for European hares (Nesvadbová and Zejda 1989; Reichlin et al. 2006). Nevertheless, it has been shown that European hares mostly did not positively select winter wheat because its availability was high compared to other food sources (Reichlin et al. 2006). This supports our findings. All other habitat types of the rough category agricultural crop land were selected differently in spring and autumn. In spring, European hares were attracted probably to germinating seeds as a food source. The habitat types which were used by European hares without significant selection in spring might not be attractive as forage because they consist either of bare ground or vegetation from the last year. In contrast, intertillage, vegetables and stubble field might offer forage for the animals in autumn.

Grassland

European hares in spring and autumn avoided grassland of any type except species-rich pastures. Jennings et al. (2006) argue that European hares from pastural landscapes obtain a good-quality diet but expend more energy and have a reduced body condition in comparison to those from arable areas. Grassland as a suboptimal habitat for European hares might therefore explain our findings of a general avoidance of this habitat type especially as our study was conducted in the plants’ dormant season. Fertilised pastures were avoided most, whereas unfertilised and therefore species-rich pastures were preferred most among the different types of grassland. Because unimproved grassland and species-rich pastures had about the same plant associations, plant diversity alone cannot explain the hares’ strong preference for species-rich pastures. Active European hares preferred sheep grazed pastures only during winter (1 February–13 March) but selected cattle pasture throughout the year (Smith et al. 2004). In addition, strong differences between vegetation height of sheep grazed fields and cattle fields during October–March have been recorded (Petrovan et al. 2011). Hence, European hares seem to use pasture differently depending on the season, vegetation height or kind of livestock. In our study, both types of pasture had about the same vegetation height, but we did not distinguish between cattle, horse or sheep pasture. We therefore conclude that the combination of high plant diversity due to omission of fertilisation and the vegetation structure, caused by grazing livestock, created a highly attractive habitat type for European hares during spring and autumn.

Unfarmed area

The category unfarmed areas comprised different habitat types. The European hares’ selection for the habitat types set-aside, field margin and fallow land was noticeably different. A possible explanation is the different vegetation structure. Since active European hares prefer open grounds with short vegetation for feeding (Tapper and Barnes 1986), we assume that the open vegetation of field margins and fallow land was preferred, whereas the more structured vegetation of set-asides was avoided. Probably for the same reason, the hedges and thickets with high and dense vegetation were negatively selected by the European hares. The European hares preferred fallow land in spring but showed no significant selection for the same habitat type in autumn. We assume that in autumn, the species finds enough alternative habitat types attractive for foraging, whereas in early spring, suitable food is less abundant and hence fallow land becomes preferred.

Urban areas

Urban areas consisted not only of residential areas but also of gardens, allotments and graveyards. European hares strongly avoided residential areas. Since gardens, allotments and graveyards contain a high variety of different plants, they might be attractive to hares. Despite this fact, European hares in our study negatively selected these habitat types. Possible explanations for this might be that, firstly, the disturbance caused by humans is considerable and, secondly, these areas are mostly surrounded by a wire fence which makes it difficult for animals to enter the property. European hares avoided roads in general. Tarred roads had the lowest preference index, whereas tracks completely vegetated had the highest preference index among the different road types. It has been argued that the vegetation along and on field tracks and unpaved roads contributes to the hares’ diet spectrum (Roedenbeck and Voser 2008). Additionally, the construction level of the road is closely linked with the amount of traffic, i.e. disturbance for the hares (Roedenbeck and Voser 2008). Both explanations fit our results.

Influence of the vegetation height on the European hares’ habitat preference

The vegetation height seemed to explain the European hares’ habitat avoidance during activity only when the vegetation was substantially high such as in set-asides. For habitat types with a marginally higher vegetation height than average, such as intertillage, vegetables or winter oilseed rape, other criteria for the hares’ selection during activity, like suitability for forage, might be more important than the vegetation structure. This supports another European hare study recording some crop types used day and night when fulfilling requirements for feeding and resting (Tapper and Barnes 1986). Moreover, for European hares, not only vegetation height but also cover value is crucial for their habitat selection (Neumann et al. 2011). Vegetation height and cover might vary in the same habitat type especially during the plants’ dormant season. A combination of vegetation height and cover value may therefore explain the European hares’ habitat preference more accurately during this time of the year.

Influence of the hare density on habitat preferences

Some habitat types such as woodland/forest, hedges, cereals and improved grassland were unattractive to the European hares in our study. When comparing our results with other studies on active European hares, it seems that these habitat types changed to being attractive when hare density increased (Tapper and Barnes 1986; Smith et al. 2004; Vidus-Rosin et al. 2009; Cardarelli et al. 2011; Bertolino et al. 2011b; Table 3). A possible explanation might be that at high densities, unpreferred habitats become attractive to European hares due to intraspecific competition for resources.

Table 3 Comparison of different studies investigating European hares’ habitat preferences during the night classified according to hare density (number of hares per 100 ha)
Full size table

Influence of the mean field size on habitat preferences

Our study animals living in an agricultural landscape with small average field sizes appeared not to select habitat types differently than animals in study areas with larger average field sizes (Table 4). This supports the findings of other studies reporting that in agricultural areas with large field sizes, European hares mostly enlarge their home-range size in order to include the required habitat types (Reitz and Léonard 1994; Stott 2003; Smith et al. 2004). Note that, regarding the influence of mean field size on the habitat preferences, the results of our active study animals were not compared to studies on European hares during activity exclusively, as information on average field size in the literature is mostly missing.

Table 4 Comparison of different studies investigating European hares’ habitat preferences classified according to field size
Full size table

Difference between the two seasons spring and autumn

European hares selected more habitat types positively (eight vs. six) but chose less habitat types without significant selection in autumn than in spring (two vs. seven). All differences between the two seasons were due to an altered habitat selection in the rough categories agricultural crop land and unfarmed areas. Possibly, these changes in habitat preferences were caused by remaining field crops getting old and new field crops starting to sprout at the end of the plants’ dormant season. In contrast, in another study on active European hares, additional changes in preferences of grassland were recorded along the seasons (Smith et al. 2004). Probably, this is due to a higher percentage of grassland in Smith’s than in our study area (71 vs. 50 %).

Conclusion

In summary, we found that substantial information was lost by pooling habitat types into broader groups in some categories. Hence, for some categories, more detail might be needed as for others when analysing hares’ habitat selection. In this agricultural area with low hare density, European hares avoided several habitat types which were preferred in other study areas with higher hare densities. Therefore, we assume that hare density has an influence on the species’ habitat selection. Moreover, the vegetation height seemed to explain the species’ habitat selection only when the vegetation was substantially high. In conclusion, our results imply that studies on habitat preferences have to be conducted in areas with low hare density to be able to gain knowledge on the species’ habitat requirement and hereinafter improve the suitability of the habitat for this species.