Differential response of mammals to agricultural fences — The effects of species vagility and body size

Abstract

An increase in wolf populations during the 1990s in North-Eastern Israel compelled livestock growers to establish fenced calving enclosures to minimize cattle predation. We hypothesized that such fences form barriers to animals traversing the landscape, to which various wildlife species may respond differentially. In order to test this, an array of line transects were established near six enclosures at which scat pellets were monitored for 23 months. We identified 1496 pellets, belonging mainly to medium or large mammal species. To estimate pellet abundance and quantify mammal activity levels we used N-mixture models. We tested the performance of seven models assuming two abundance distribution functions: Poisson and zero-inflated Poisson (ZIP) distribution models which evaluated different combinations of explanatory variables: effects of time, enclosure and transect. Model selection was performed using the Akaike Information Criterion (AIC). Pellet counts and mean estimated abundance were greater in transects external to the enclosures, for all species combined, mountain gazelle (Gazella gazella) and wild boar (Sus scrofa). Additionally, two behavioral responses to the presence of protective fences were observed. Outside the enclosures a U-shaped response of decrease in abundance at a distance of 50m from the fence followed by an increase towards the distant transects at 200–700m from the fence. Inside the calving enclosures a decreasing abundance response was observed, which was negatively correlated with distance from the fence. This study identifies the spatial effects emerging from the presence of protective fences as habitat-fragmenting agents. It suggests that a protective fence imposes a habitat-independent behavioral filter at the landscape level which could be related to species vagility and body size. Inconsistent activity responses of the different species to the presence of fences are repeatedly observed, providing support for our initial hypothesis.