Side effects of rodent control on non-target species: Rodenticides increase parasite and pathogen burden in great bustards

For many years anticoagulant rodenticides have been used in vole control campaigns, in spite of the proven risk of secondary poisoning of non-target predators and scavengers. In this paper we analyse for the first time great bustard exposure and intoxication by anticoagulant rodenticides in Spain, based on residues found in the livers of 71 bustard carcasses collected during 1991–2010. Ten individuals contained chlorophacinone and one flocoumafen. Chlorophacinone level was significantly correlated with the pathogen and parasite burden of intoxicated birds. Moreover, through the last 12 years the annual number of great bustards that present chlorophacinone in liver collected in our study areas was correlated with vole peaks at a nearby area, suggesting that the ingestion of rodenticide was proportional to the amounts spread in the fields. We conclude that rodenticide consumption is a regular event among great bustards when baited cereal is spread on fields, and that this may cause chronic weakening of intoxicated individuals, possibly affecting their survival. Future rodent control actions should consider these negative side effects on non target granivorous steppe and farmland species, particularly when they are globally threatened.

► Non-target species rodenticide secondary poisoning is shown in the great bustard. ► Chlorophacinone was the most common found rodenticide, but flocoumafen appeared also. ► Chlorophacinone level was correlated with the pathogen and parasite burden of intoxicated bustards. ► Chlorophacinone annual frequency in dead bustards was correlated with vole peaks. ► Great bustards regularly consume baited rodenticides, affecting their survival.