title: Prey composition modulates exposure risk to anticoagulant rodenticides in a sentinel predator, the barn owl.
abstract: Worldwide, small rodents are main prey items for many mammalian and avian predators. Some rodent species have pest potential and are managed with anticoagulant rodenticides (ARs). ARs are consumed by target and non-target small mammals and can lead to secondary exposure of predators. The development of appropriate risk mitigation strategies is important and requires detailed knowledge of AR residue pathways. From July 2011 to October 2013 we collected 2397 regurgitated barn owl (Tyto alba) pellets to analyze diet composition of owls on livestock farms in western Germany. 256 of them were fresh pellets that were collected during brodifacoum baiting. Fresh pellets and 742 liver samples of small mammals that were trapped during baiting in the same area were analyzed for residues of ARs. We calculated exposure risk of barn owls to ARs by comparing seasonal diet composition of owls with AR residue patterns in prey species. Risk was highest in autumn, when barn owls increasingly preyed on Apodemus that regularly showed AR residues, sometimes at high concentrations. The major prey species (Microtus spp.) that was consumed most frequently in summer had less potential to contribute to secondary poisoning of owls. There was no effect of AR application on prey composition. We rarely detected ARs in pellets (2 of 256 samples) but 13% of 38 prey individuals in barn owl nests were AR positive and substantiated the expected pathway. AR residues were present in 55% of 11 barn owl carcasses. Fluctuation in non-target small mammal abundance and differences in AR residue exposure patterns in prey species drives exposure risk for barn owls and probably other predators of small mammals. Exposure risk could be minimized through spatial and temporal adaption of AR applications (avoiding long baiting and non-target hot spots at farms) and through selective bait access for target animals.
authors.affiliation: Julius Kühn Institute, Federal Research Centre for Cultivated Plants, Institute for Plant Protection in Horticulture and Forests, Vertebrate Research, Toppheideweg 88, 48161 Münster, Germany; University of Münster, Institute of Landscape Ecology, Heisenbergstrasse 2, 48149 Münster, Germany. Electronic address: anke.geduhn@jki.bund.de.
authors.forename: Anke
authors.initials: A
authors.lastname: Geduhn
authors.affiliation: Julius Kühn Institute, Federal Research Centre for Cultivated Plants, Institute for Plant Protection in Horticulture and Forests, Vertebrate Research, Toppheideweg 88, 48161 Münster, Germany.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Esther
authors.affiliation: Julius Kühn Institute, Federal Research Centre for Cultivated Plants, Institute for Ecological Chemistry, Plant Analysis and Stored Product Protection, Königin-Luise-Strasse 19, 14195, Berlin, Germany.
authors.forename: Detlef
authors.initials: D
authors.lastname: Schenke
authors.affiliation: Julius Kühn Institute, Federal Research Centre for Cultivated Plants, Institute for Crop and Soil Science, Bundesallee 50, 38116 Braunschweig, Germany.
authors.forename: Doreen
authors.initials: D
authors.lastname: Gabriel
authors.affiliation: Julius Kühn Institute, Federal Research Centre for Cultivated Plants, Institute for Plant Protection in Horticulture and Forests, Vertebrate Research, Toppheideweg 88, 48161 Münster, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Jacob
mesh_terms: D000818:Animals; D000925:Anticoagulants / Q000378:metabolism*; D003411:Arvicolinae / Q000378:metabolism; D004781:Environmental Exposure / Q000706:statistics & numerical data*; D004784:Environmental Monitoring; D005858:Germany; D012306:Risk; D012378:Rodenticides / Q000378:metabolism*; D020305:Strigiformes / Q000378:metabolism*
chemical_list: D000925:Anticoagulants; D012378:Rodenticides
keywords: Barn owl; Brodifacoum; Diet; Non-target; Secondary poisoning; Small mammal