Effects of anticoagulant rodenticide poisoning on spatial behavior of farm dwelling Norway rats

Abstract

Commensal rodent species cause damage to crops and stored products, they transmit pathogens to people, live-stock and pets and threaten nativeflora and fauna. Tominimize such adverse effects, commensal rodentsare pre-dominantly managed with anticoagulant rodenticides (AR) that can be transferred along the food chain. Wetested the effect of the uptake of the AR brodifacoum (BR) by Norway rats (Rattus norvegicus) on spatial behaviorbecause this helps to assess the availability of dead rats and residual BR to predators and scavengers. BR was de-livered by oral gavage or free-fed bait presented in bait stations. Rats were radio-collared to monitor spatial be-havior. BR residues in rat liver tissue were analyzed using liquid chromatography coupled with tandem massspectrometry. Norway rats that had consumed BR decreased distances moved and had reduced home rangesize. Treatment effects on spatial behavior seemed to set in rapidly. However, there was no effect on habitat pref-erence. Ninety-two percent of rats that succumbed to BR died in well-hidden locations, where removal by scav-enging birds and large mammalian scavengers is unlikely. Rats that ingested bait from bait stations had 65% higher residue concentrations than rats that died from dosing with two-fold LD50.Thissuggestsanoverdosingin rats that are managed with 0.0025% BR. None of the 70 BR-loaded rats was caught/removed by wild preda-tors/scavengers before collection of carcasses within 5-29 h. Therefore, and because almost all dead rats diedin well-hidden locations, they do not seem to pose a significant risk of AR exposure to large predators/scavengers at livestock farms. Exposure of large predators may originate from AR-poisoned non-target small mammals. Thefew rats that died in the open are accessible and should be removed in routine searches during and after the ap-plication of AR bait to minimize transfer of AR into the wider environment. © 2021 The Authors. Published by Elsevier B.V.