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Anticoagulant rodenticides may pose a secondary poisoning hazard to non-target predators and scavengers because of the time-delay between ingestion of a lethal dose and death of a target rodent. We investigated some pre-lethal effects of an anticoagulant rodenticide on the behavior of wild rats in cages and in enclosures. We found that social interactions shortened time to death, that most rats died away from cover and that thigmotactic behavior was reduced in the enclosures. The normal light-dark rhythm was upset in intoxicated rats in both cages and enclosures. Thus pre-lethal effects are likely to alter the exposure of predators and scavengers to intoxicated rats, and diurnal predators may be exposed more than nocturnal predators as a consequence. We stress the need to extend these behavior studies to the field.