Site use of grazing cattle and sheep in a large-scale pasture landscape: A GPS/GIS assessment

Year-round mixed-species grazing at low densities in large-scale pasture systems has become a popular conservation concept as it is assumed to maintain the valuable biodiversity of semi-open cultural landscapes. This study aims to elucidate which vegetation types are preferentially grazed by cattle and sheep and whether the grazing animals change their preferences through the seasons so that year-round grazing leads to a utilization of all habitats. Additionally, we wanted to determine the main factors underlying the site use patterns of the animals. The study was conducted on 180ha of a nature reserve and former military training area in northern Germany from January to October. Within this area, the positions of one cattle herd and one sheep flock were simultaneously recorded every 5min using the global positioning system (GPS). For this purpose, we fitted one GPS collar alternately to three different cows and another to three different sheep. If the position of a collared animal had changed more than 6m but less than 100m within 5min grazing was assumed based on a validation of these thresholds by direct observation. Using a geographic information system, we analysed the location data with regard to vegetation characteristics, altitude, and distance from fences, water sources, and a sheep shed. For each month, we determined Ivlev's electivity index of both herbivore species in relation to eight broad vegetation types. We used multiple linear regression to create models that describe the grazing frequencies in the grid cells of the area depending on parameters of those grid cells and their spatial position. Cattle preferred moist and productive habitats, whereas sheep preferred dry and nutrient-poor habitats. Only when feed was in extremely short supply, the animals switched to sites they had previously avoided. Differences in the spatial preferences of the two species were more marked than seasonal changes. Spatial demands of cattle and sheep were largely complementary. Grazing sites with better water availability (i.e. lower distance from the drinking trough and ponds) were significantly preferred by cattle. The sheep preferred grazing sites close to their shed. Our results show that only a combination of different herbivores guarantees that all habitats of such a large low-intensity pasture are grazed and thus are kept in a management status favourable to conservation. However, the positioning of drinking troughs, fences, and sheds should be carefully considered as these facilities seriously influence the site use of the animals.