ORIGINAL PAPER The diet of Danish red foxes (Vulpes vulpes) in relation to a changing agricultural ecosystem. A historical perspective Sussie Pagh 1 & Rune Skjold Tjørnløv 2 & Carsten Riis Olesen 3 & Mariann Chriel 4 Received: 21 October 2014 /Accepted: 24 August 2015 # Mammal Research Institute, Polish Academy of Sciences, Białowieża, Poland 2015 Abstract Rodents and especially voles (Microtus agrestis or arvalis) make up the basic diet of foxes (Vulpes vulpes) in Denmark. As the abundance of voles and mice may have decreased as a result of modern agricultural procedures, this study investigates potential changes in the diet of Danish red foxes over the past 4 decades in relation to a changing agri- cultural landscape. Our study compares the stomach contents of foxes collected in Jutland during the years 2012–2014 with a similar study from 1965 to 1970. The results show that small rodents occur in the stomachs of foxes with the same frequen- cies today (73 %) as 40–50 years ago (67 %), while the fre- quency of European brown hare (Lepus europaeus) has de- creased from 7 to 3 % and the frequency of roe deer (Capreolus capreolus) has increased from 3 to 18 %. The changes in the occurrence of brown hare and roe deer in the diet of foxes during the past 40 years most probably reflect changes in the populations of the two species. By comparing digitised orthophotos of six agricultural areas (3.5×3.5 km) of the past 1974/1975 and present landscapes, it was revealed that the total area of crop fields, small natural habitats, hedge- rows and grasslands have remained almost unchanged. How- ever, mean field size has increased by 48 %, and the mean size of small natural habitats has increased by 15 %; meaning that the length of field boundaries and the number of small natural habitats have decreased by 65 and 33 %, respectively. The distance between natural habitats in the cultivated areas has become larger during the past 40 years. Overall, the areas of natural biotopes have remained the same in Denmark during the past 40 years. Field boundaries on the other hand which are known to be important vole habitats have become fewer in the cultivated areas. Despite this, small rodents still occur in high frequencies in the diet of nowadays foxes. As voles are sensitive to fragmentation, narrow stipes of permanent grass should be maintained or even re-established in the cultivated areas to improve life conditions for small rodents and other wildlife. Keywords Food . Rodents . Vole . Microtus . Game species . Roe deer . Capreolus capreolus . European brown hare . Lepus europaeus . Partridge . Perdix perdix . Fragmentation Introduction Intensified farming methods have in a relatively short period of time altered the flora and fauna of the agricultural ecosys- tem, in favour of some species and to the disadvantage of others: European brown hare (Lepus europaeus) populations have declined throughout most of Europe since the1960s (Schmidt et al. 2004, 2005; Roedenbeck and Voser 2008; Reynolds et al. 2010), and populations of grey partridge (Perdix perdix) have decreased dramatically (Bro et al. 2000; Potts 1986; Potts et al. 2010; Kuijper et al. 2009; Aebischer and Ewald 2010; Topping et al. 2010). In contrast, populations of roe deer ( Capreolus capreolus ), mallard ( Anas platyrhynchos) and greylag goose ( Anser anser) have Communicated by: Matthew W. Hayward * Sussie Pagh sussiepagh@gmail.com 1 FO-Aarhus, Frederiksgade 78C, Aarhus, Denmark 2 Department of Bioscience, Aarhus University, Frederiksborgvej 399, Roskilde 4000, Denmark 3 Danish Hunters Association, Molsvej 34, 8410 Rønde, Denmark 4 Section for Diagnostics and Scientific Advice, National Veterinary Institute DTU, DK-1790 Copenhagen, Denmark Mamm Res DOI 10.1007/s13364-015-0244-y