The diet of migrant Red Kites Milvus milvus during a Water Vole Arvicola terrestris outbreak in eastern France and the associated risk of secondary poisoning by the rodenticide bromadiolone

Abstract

Poisoning by pesticides is considered one of the primary threats to the Red Kite Milvus milvus. We studied the diet of this raptor in an area of eastern France where the rodenticide bromadiolone is widely used to control Water Vole Arvicola terrestris outbreaks. A high degree of specialization for Water Voles was noted, as their remains were identified in all 119 pellets collected in autumn 2008, whereas other small rodent species and insects occurred in 27 and 9% of pellets, respectively. We estimated that Water Voles constituted 94% of the total biomass ingested by Red Kites under these conditions. Based on these data, the risk of secondary poisoning due to feeding on poisoned voles was assessed. Acute exposure on a single day was not considered a risk for Kites, but exposure to poisoned voles over 1 week represented the maximal risk for the Red Kite; the calculated dose of bromadiolone ingested by a Red Kite was 137 times higher than the toxicological benchmark for birds. A field survey in the studied area detected four dead Red Kites and one moribund bird in autumn 2008 but did not confirm that the cause of death was bromadiolone poisoning. We suggest that professional monitoring is needed to assess the impact of rodenticides on Red Kites in areas where voles are controlled.

Poisoning by Anticoagulant Rodenticides in Humans and Animals: Causes and Consequences

“…Pesticide usage has been correlated with non-target wildlife exposition [74,75], and the intensity of treatment was related to incidence on local fox populations in France [80]. Finally, the diet is certainly going to inluence secondary exposition and species like raptors, foxes and mustelids largely feeding on rodents when abundant are consequently the most at risk, as demonstrated for the red kite (Milvus milvus) [81]. The removal of visible rodent bodies helps to reduce the risk of secondary exposition [82] but is not always possible because of landscape limited access and in the case of aerial application [1].…”

Shooting is still a main threat for raptors inhabiting urban and suburban areas of Rome, Italy

“…Beside these low occurrences, it is important to consider that several recent specific studies found high exposure to anticoagulant rodenticides in liver tissues of the raptor species (Thomas et al 2011;Christensen et al 2012;Coeurdassier et al 2012;Hughes et al 2013). Moreover, we need to acknowledge our limits in correctly identifying the poisoning and debilitation cases, not having performed toxicological tests.…”

Scavenging of rodent carcasses following simulated mortality due to field applications of anticoagulant rodenticide

“…Thus, during water vole outbreaks, high densities of red kites and other raptors are commonly noticed during several days or weeks because these rodents represent a large biomass of available food. In such context, it was previously showed that red kites exhibit a high degree of diet specialization on water vole and that this may led to lethal poisoning if they stage in areas treated with the bromadiolone for one week (Coeurdassier et al 2012).…”

“…It was notably shown that the residues measured in rodents trapped alive may lead to daily doses higher than LD50 (the median lethal dose) determined for different predators (Coeurdassier et al 2012;Giraudoux et al 2006;Tosh et al 2011). However, following experimental exposure to ARs, it was observed that poisoned rats changed their behavior, half of the monitored specimens dying away from cover, and so, were more vulnerable to predation (Cox and Smith 1992).…”