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Is rodenticide use disrupting the natural autoregulation of vole populations?

Periodic Reporting for period 1 - VOLES (Is rodenticide use disrupting the natural autoregulation of vole populations?)

Reporting period: 2015-11-16 to 2017-11-15

What is the problem/issue being addressed? Vole populations can attain extremely high densities during their multiannual population cycles (Krebs 2013). As a result, they produce damages in agriculture lands and are controlled with anticoagulant rodenticides by some farmers (Sage et al. 2008, Delattre and Giraudoux 2009). That poses a human-wildlife conflict because vole control reduces the amount of key food sources for predators but also increases the risks of secondary poisoning to predators that eat intoxicated voles (Delibes-Mateos et al. 2011, Coeurdassier et al. 2014). If predator populations are eliminated there may be higher chances of recurrent vole outbreaks and thus long-lasting need of controlling the vole population by rodenticides.

Why is it important for society? Vole damages may inflict economic losses up to of 10000 € for each worker unit in farms during an entire cycle (Schouwey et al. 2014). Using rodenticides can impose higher costs for production and thus reduce the profits of farmers (Stenseth et al. 2003). In addition, society is increasingly concerned about the origin of products, the way they are produced and the potential side effects of the use of pesticides given their negative effects on biodiversity and public health (Jacquot et al. 2013, Mitchell et al. 2017).

What are the overall objectives? To study the role of rodenticides as super-predator that eliminates both voles and predator populations, through the transfer of this pesticide within the trophic chain. Moreover, to understand the demographic impacts that rodenticides may have on the long term. In addition, to explore protocols of rodenticide application beneficial for both agriculture and conservation.

Conclusions: Anticoagulant rodenticides may produce population declines in voles and their predators like small mustelids (weasels and stoats). The findings obtained here from model show the super-predator role of anticoagulant rodenticides, affecting the population dynamics of predators and voles. For treatments carried out homogeneously over large areas, this happens especially with rodenticide application at very low vole densities, which produce the deepest declines in small mustelid populations and favors further treatments to buffer the vole population growth. To reach consensus between farm production and conservation purposes, the best way to apply rodenticides would include treatment during the increase phase of vole population cycles, with low quantity of bromadiolone and time breaks of treatment stop, in which vole and predator populations are maintained. Anyway, the results of the modeling part are non-spatial and should be further validated. This is because, in real conditions, treatment is not conducted in all agricultural parcels and there are refuges, for instance, woodlands. Therefore, next steps should take into account this spatial heterogeneity.
Work performed: We conducted a biomathematics study in parallel with active field monitoring of our study system of voles, predators and farmers using bromadiolone, the anticoagulant rodenticide allowed for vole control in agricultural properties in France.
Overview of results: We observed that small mustelids may suffer population declines in areas frequently treated with bromadiolone, in contrast with sites with low frequency of treatment. The declines were deeper in sites with low water vole densities and frequent treatment. We found presence of rodenticides in vole livers in parcels recently treated and small mustelid scats at frequently treated sites, which shows exposure in these populations. The population declines in small mustelid populations has also been observed based on modelling. From both experiences we observed that treating with anticoagulant rodenticides at very low water vole densities could have catastrophic consequences for predators. Farmers would then be obliged to treat frequently to counter the quick population growth of voles, free of losses from predation.
Exploitation and dissemination: We participated in the congresses EASYs (France), SETAC Europe (Belgium), and EVPMC (Poland). Additionally, we organized a seminar with stakeholders, hunters, pest managers, students and researchers of our Laboratory to present these and other results obtained in the research line of our group. The results presented are being prepared as manuscripts for submission. Nevertheless, the presentations and preliminary results are publicly available as they have been uploaded as videos (see The peer-review journal “Pest Management Science” has shown interest for publishing part of them in a special issue after the EVPMC congress.
Moreover, we presented our project in educative centers, participated in the European Researchers’ night, and appeared in radio tracks and internal University publications. Javier Fernandez-de-Simon also conducted a secondment in the Doubs Hunting Federation (FDC25), a non-academic partner of the project. All these events and project’s actions have been publicly advertised in our blog, social media, by posters/flyers in University, etc.
The latest studies show that the diffusion of anticoagulant rodenticides at regional levels is quite widespread in general (Topping and Elmeros 2016, Ruiz-Suárez et al. 2016). However we know very little in terms of long-term impacts of rodenticides on population dynamics of predators. Our biomathematics modelling experience will be a strong contribution in this regard. For that reason we plan to submit the manuscript to a journal of high Impact factor such as Journal of Applied Ecology. The results will be very influential as a breakthrough in order to explore the pesticide transfer and impacts on the long term. It also illuminates our knowledge on the best protocols of rodenticide application, which can guide management and conservation decisions. The field results on small mustelids adds crucial information of the population impact of rodenticides in the European context. All of them provide revolutionary insights of how pesticides affect biodiversity.
Stoat and the molecule bromadiolone, anticoagulant rodenticide used for vole control