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Widespread anticoagulant poison exposure in predators in a rapidly growing South African city

Laurel E.K. Serieys, Jacqueline Bishop, Nicola Okes, Joleen Broadfield, Deborah Jean Winterton, Robert H. Poppenga, Storme Viljoen, Robert K. Wayne, M. Justin O'Riain
Science of the total environment 2019 v.666 pp. 581-590
Aonyx capensis, Bubo, Caracal caracal, Genetta tigrina, Herpestidae, Mellivora capensis, anticoagulants, bioaccumulation, biodiversity, blood, forage, habitat destruction, invertebrates, issues and policy, linear models, liver, predators, risk factors, rodenticides, toxicity, trophic levels, vines, vineyards, wildlife, wildlife habitats, South Africa
Anticoagulant rodenticides (ARs) are used worldwide to control rodent populations. ARs bioaccumulate across trophic levels and threaten non-target wildlife. We investigated the prevalence of AR exposure in seven predator species in the rapidly developing Greater Cape Town region of South Africa – a mosaic of natural, urban, and agricultural areas within a global biodiversity hotspot. We focused sampling on caracals (Caracal caracal, n = 28) as part of a larger caracal ecology study, but also opportunistically sampled Cape Clawless otters (Aonyx capensis, n = 9), large-spotted genets (Genetta tigrina, n = 4), honey badger (Mellivora capensis, n = 1), water mongoose (Atilax paludinosus, n = 1), small gray mongoose (Galerella pulverulenta, n = 1), and Cape Eagle owl (Bubo capensis, n = 1). We tested livers from all species, and blood from ten caracals, for eight AR compounds to assess prevalence and amount of exposure for each compound. We used generalized linear models to test spatial, demographic, and seasonal risk factors for ten measures of AR exposure in caracals. We detected at least one of the four most toxic AR compounds in six species. Exposure was high for caracals (92%) and all species combined (81%). For caracals, proximity to vineyards was the most important AR exposure risk factor. Vineyards in Cape Town do not use ARs to protect their vines but do host commercial hospitality structures where ARs are used. Vineyards may thus link caracals that forage within vineyards to the rat poisons used in and around their commercial structures. Residue levels were unexpected in large-spotted genets and Cape Clawless otters, suggesting invertebrate vectors. ARs may present a cryptic threat to populations already vulnerable to increasing habitat loss, vehicle collisions, poachers and fire. Targeted mitigation should include a mix of environmentally responsible policies that reduce AR use, particularly in areas near wildlife habitat.