1. Introduction
Recent advances in precision livestock farming technologies, such as GPS-based virtual fencing, allow for greater control of grazing pastures and easier monitoring of animals, providing potential benefits for both production, nature conservation and animal welfare [
1,
2,
3]. This is especially true in areas with sloped and hilly terrain where traditional physical fencing can be challenging and labour intensive [
4,
5]. In the last few decades, there has been an increased focus on monitoring livestock in both production and nature conservation settings to make better and more informed management decisions [
6,
7,
8,
9]. Especially the habitat use and behaviour of cattle in regards to environmental concerns and animal welfare are of high interest [
7,
9,
10,
11]. Understanding habitat preferences of grazing livestock and their use of the grazing areas, is important to help develop a more sustainable livestock grazing system with minimal negative impact on the environment [
11]. Multiple studies have investigated the habitat use by free-ranging livestock to make better management decisions and promote resource conservation [
12,
13,
14,
15]. Cattle are generally less selective in their feed preferences compared to other grazing livestock such as sheep and goats [
16]. They prefer habitats with a high biomass production such as meadows and grasslands but are also used in nature conservation on salt meadows and heathland with lower biomass production [
15,
17]. However, because grazing resources are often spatially and temporally heterogeneously distributed, animals need to visit different habitats to satisfy all their nutritional needs [
13]. In addition, terrain characteristics such as the steepness of slopes and the distance to drinking water also affect the habitat selection of cattle [
13,
14,
15]. The habitat distribution of cattle is furthermore affected by temperature, protection from pests, and shelter from the elements [
18]. GPS-based systems with built-in accelerometers can be used to monitor both spatial distribution of animals and their movement, which can potentially allow monitoring of animal behaviour and activity [
19]. The collected data can be used to monitor variations in daily animal activity and help characterise typical behavioural patterns which make it feasible to detect deviations when they occur, thereby making it possible to detect potential disease and/or welfare concerns remotely [
11,
20].
The currently most used method for monitoring activity and classifying behaviour of livestock in recent years has been tri-axial accelerometer data [
19,
21,
22]. An example of this can be found in a recent paper by Versluijs et al. [
19], where accelerometer data from a virtual fencing system was used to accurately classify the behaviour of beef cattle in a natural setting. This method, although displaying high fidelity in classifying behaviour in shorter time frames, quickly drains the system of power and is therefore not usable when considering constant long-term monitoring. This limits research to short consecutive periods [
19]. To enable longer term studies with continuous data, and constant year-round monitoring, a method needs to be developed based on far simpler, and less power-consuming data. In this paper, we explore the possibility of determining habitat preference and habitat utilisation patterns using low frequency location data and a coarse measure of activity. Habitat preference is defined by Matthiopoulos et al. [
23] as: The ratio of habitat usage over its availability. Habitat utilisation patterns is loosely defined by us as: At what time of day and in which way do the animals use each habitat, e.g. do the animals use a habitat mainly for grazing or for resting. We do this by (1) calculating habitat selection ratios, (2) determining daily activity patterns and based on those, (3) inferring grazing and resting sites in a group of grazing cattle wearing virtual fencing collars. All three of these criteria must be met for the method to be considered successful.
4. Discussion
By combining GPS data from a group of cattle wearing virtual fencing collars, and mapping of habitats from publicly available field data and aerial photos, we successfully mapped habitat preference of the herd of cattle within the virtual enclosure. This method has previously been shown to be an effective way of assessing habitat preference and as an estimate of grazing pressure [
34]. In this study, the herd showed a clear preference for salt meadows, as evidenced by the significantly higher selection ratio for this habitat 6.78±0.36 (median±MAD) compared to all other habitats 1.32±0.04 (median±MAD) to 0.47±0.04 (median±MAD). This preference for salt meadows is not immediately logical according to existing literature, as cattle generally prefer grazing on drier habitats, as these tend to have vegetation with higher crude protein and lower fibre content than wet habitats [
11,
35], although one study has found cattle to preferentially graze wet areas [
36]. In a previous study in a mosaic landscape of sand-dunes and lowland habitats, somewhat comparable to this area, cattle also preferred grazing in the lowland habitats [
37]. This seemingly counter-intuitive preference could be a result of what other habitats are available. Across several studies, the least preferred vegetation for grazing by cattle is half-shrubs, such as heather (
Calluna vulgaris), irrespective of cattle breed and season [
34,
38,
39]. This would explain the preference of salt meadows over both decalcified dunes and grey dunes, which are usually characterised by heather [
40]. Likewise, humid dune slacks are generally dominated by sedges, which cattle also tend to avoid when other options are available [
35,
40]. Another explanation for the preference of salt meadows over other habitats is the productivity of the habitat. Studies suggest that cattle prefer habitats characterised by high biomass production [
15,
34,
39], and of the five classified habitats in the study area, salt meadows have the highest biomass production and highest nutritional value for cattle [
17,
41]. The least preferred habitat in this study was wooded dunes with a selection ratio of 0.47±0.04 (median±MAD). This is in line with previous studies, that have found cattle to avoid wooded areas and have higher occupancy of open grassland in both extensive and intensive grazing conditions [
12,
42,
43].
Despite not being able to directly quantify habitat utilisation in this study, we were able to identify some general trends based on patterns in activity and differences in habitat selection ratios. Quantifying habitat utilisation would require classification of behaviours as done by others, such as Ungar et al. [
6] and Versluijs et al. [
19]. This would necessitate higher frequency of data collection and in-field observations for training a classification model. In accordance with existing literature, we found that cattle spend a majority of the day at low activity levels (median of 13 hours/day) [
27,
44], and that cattle exhibit periods of high activity during early morning and late afternoon, with periods of low activity in between (
Figure 4) [
26]. The high level of variation in activity during daytime hours, is most likely due to combined effects of weather and season (
Figure 4) [
25,
26,
27]. Effect of season is especially pertinent in this study, as the length of the day has been shown to significantly affect the activity and behaviour of cattle [
25,
26,
27]. The period of data collection was characterised by a shortening of the day from around 17 hours of daylight to 10.5 hours (Source:
WorldData.info, retrieved on 19/12/2023). Based on previous studies, we can infer that a low activity level likely covers behaviours such as resting and ruminating, while high activity is a sign of grazing and/or walking [
6,
27,
44,
45]. These inferences indicate, that while the herd of cattle preferentially stayed on the salt meadows, they might have predominantly used the area for resting and ruminating rather than grazing, as most of the time spent on salt meadows was during periods of generally low activity (
Figure 5, Salt meadows). Previous studies have shown cattle to prefer resting and ruminating near water sources and on nutrient-rich vegetation [
11,
46]. However, cattle also seem to prefer grazing near water sources[
11,
36], which could explain why the most presences in humid dune slacks were recorded during high activity periods (
Figure 5, Humid dune slacks). Humid dune slacks were one of the least preferred habitats (23.1±1.49 points/ha), and the majority of grazing has likely not taken place there. The relative preferential use of decalcified dunes and wooded dunes during night hours, and grey dunes during hours of daylight, is likely due to the weather patterns of the study site. Climate and weather plays a major role in explaining animal behaviour and habitat use [
11]. Due to the location, topography and vegetation of the different habitats at this particular study site, decalcified dunes and wooded dunes would have provided the most cover against the prevailing winds at the study site, with grey dunes providing the least amount of cover. Wooded dunes would also have provided natural shelter against precipitation [
11]. It is highly unlikely that much grazing has happened in the decalcified and wooded dunes, as the majority of the time spent there by the cattle was at low activity levels, and during night hours when cattle have been shown to avoid grazing (
Figure 5) [
35].
Our results showed that GPS data and a coarse measure of activity, combined with accurate mapping of habitats can be an effective tool in assessing habitat preference and general trends in habitat utilisation. Additionally, by utilising existing technology integrated in virtual fencing systems, this is a cheap and effective method of monitoring cattle in extensive settings, without the need for additional sensors [
11]. There are, however, some apparent drawbacks to using the data from virtual fencing systems, as quantification of habitat utilisation was not possible. One potential easy improvement to the method of this study, is to include the distance the animal has travelled between two activity recordings. This simple addition would likely allow for more accurate behaviour classification, as done by Ungar et al. [
6] and Ganskopp et al. [
47]. Another potential improvement is recording activity counts in two-dimensions (fore-aft and left-right). This also allows for greater fidelity in behaviour classification and is a widespread method [
6,
9,
45]. The downside to this method is that it usually requires purpose made equipment and a higher frequency of data collection [
9]. Alternatively, using tri-axial accelerometer data provides the highest fidelity in classifying behaviour but also requires the highest frequency of data collection [
19]. This method is possible using the same virtual fencing system as used in this study, but requires purpose made firmware and quickly drains the system of power [
19]. We believe that although the method used in this study does not allow for fine detail analysis, it does provide some general insights into habitat use and preference of cattle, that can be useful for management decisions. Although this study was limited to around three months of data collection, our method allows for year-round studies. This is important, as habitat use of cattle has been shown to be season dependent [
11,
13].
Author Contributions
Conceptualisation, M.F.A., S.K.S., M.A., A.K.O.A., C.S., D.B., J.F. and C.P.; methodology, M.F.A., S.K.S., M.A. and C.P.; formal analysis, M.F.A., S.K.S. and M.A.; investigation, M.F.A., S.K.S. and M.A.; data curation, M.F.A., S.K.S. and M.A.; writing—original draft preparation, M.F.A., S.K.S. and M.A.; writing—review and editing, M.F.A, S.K.S, M.A., A.K.O.A, C.S, D.B., J.F. and C.P.; visualisation, M.F.A., S.K.S. and M.A.; supervision, A.K.O.A, C.S, D.B., J.F. and C.P. All authors have read and agreed to the published version of the manuscript.