Non-invasive method to monitor fox exposure to bromadiolone after rodent population control – feasibility studies in situ
Résumé
Pesticides are used for invasive and pest species regulations. Evidence of their negative impact on wildlife has been provided worldwide. In some countries, particularly in Europe, bromadiolone, a Second Generation Anticoagulant Rodenticide (SGAR), is intensively used in the field for controlling the population outbreaks of the Water vole Arvicola terrestris. Among non target species, dozens to hundreds of secondary poisonings of Red foxes Vulpes vulpes have been reported each year. To date, SGAR monitoring has been carried out only based on necropsy and toxicological investigation of carcasses. We have shown that the molecule is measurable in faeces of captive foxes fed with bromadiolone-contaminated voles. The present work aims at (1) assessing the feasibility of bromadiolone analysis in faeces collected in situ, (2) determining if there is a relationship between direct (liver residues) and indirect (faeces bromadiolone residues) markers of exposure. In a 50 km² area, 48% of the faeces collected 15 to 45 days after treatment contained bromadiolone. In an other area of 125 km² treated 1 to 6 month before sampling, 85% of fox livers and 29% of faecal pellets from rectum, contained bromadiolone. We demonstrated an exponential relationship between pellet and liver concentrations. This may suggest a gradient between animals having been exposed long ago and those exposed more recently. Our results indicate that bromadiolone analysis in faeces can be a sensitive and non-invasive tool, and pave the way for further studies aiming at assessing fox population exposure at large spatial scale, before any mortality hazard.