Toxic load at the top of the food chain: Eurasian Lynx exposed to anticoagulant rodenticides in Switzerland

Wild mammals are widely exposed to anticoagulant rodenticides (ARs). This was demonstrated for both rodent predators and carnivores eating mainly large prey such as wolf or Mountain lion. To date, only little information is available on the exposure of the Eurasian lynx to ARs, a top predator endangered in Western Europe. Here, we monitored the liver concentrations of ARs in 123 Eurasian lynxes collected during 2014-2022 in Switzerland, a country that hosts one of the main populations in this part of its range. Relations between AR concentrations and health indicators like iron deficiency, body condition, mange occurrence or the likelihood for a lynx to be hit by a vehicle were checked. Thirty-three percent of the individuals had AR residues in the liver, among which 60% were exposed to more than one active ingredient. Brodifacoum, bromadiolone and difenacoum were the most frequently detected. In individuals positive to ARs, the summed concentrations ranged between 0.009 - 0.51 µg/g ww. Hepatic AR concentrations were higher than 0.2 µg/g for 4% of the lynx. We show that subadults were more exposed than juveniles and that residue occurrence is higher during the breeding period. No relation was found between AR occurrence and iron concentrations in liver, body condition, mange occurrence or the probability for a lynx to be hit by a vehicle. The present findings highlight a concerning situation regarding the exposure of this feline to second-generation compounds in this key area for its conservation in Western Europe. Further investigation based on more sensitive endpoints related to coagulopathy, reproduction and immune function are still needed to diagnose whether ARs impact lynx health and contribute to threat population viability.