Large-scale sampling of small mammals throughout the year

Abstract

Small mammals are a staple food for many predator species determining their abundance, distribution, and diversity (Butet, Paillat & Delattre 2006). The abundance of small mammals in agricultural landscapes varies between different habitat types and throughout the year. Mechanical disturbance through harvesting, ploughing and tillage removes shelters, destroys nests and burrows and decrease food availability for small mammals (Tew & Macdonald 1993). Consequently, intensively cultivated agricultural fields might become inhospitable for small mammals, which might only persist in habitat patches with undisturbed areas such as hedges, ditches, road verges, set-aside and wildflower areas (Arlettaz et al. 2010). However, the spatial patterns of occurrence of small mammals, especially over larger areas, are poorly investigated. We studied distribution, abundance and fluctuation of small mammal populations over larger areas and in different habitat types throughout the year. The abundance of small mammals was measured with indirect methods, i.e. field signs and track plates in four regions in Switzerland. We sampled field signs like runways, holes and molehills along transects of 5 m length and set a track plate during three days close to each transect. Our results show that the abundance of small mammals not only fluctuated in annual cycles but also highly between seasons and habitat types. Over larger areas, fluctuations were not synchronous but highly variable between the sampled regions and habitat types. Small mammal populations crashed down in agricultural fields after harvesting, while populations remained more stable during the whole year in less disturbed structures such as hedges and ditches. Such large annual, seasonal and spatial variation patterns might highly determine prey availability for predators and are of major importance for many endangered farmland species feeding on small mammals such Barn Owls and Stoats. Monitoring small mammal populations through indirect methods is a good alternative compared to live-trapping because it allows covering much larger areas with similar efforts. It provides a temporal and spatial resolution which cannot be achieved by live-trapping. Such large-scale samplings of small mammals could help improving conservation measures on larger scales, especially for predator species living in farmlands.