Control of Norway Rats in the Agricultural Environment: Alternatives to Rodenticide Use

The control of Norway rat populations on farms in the UK currently relies heavily on the use of anticoagulant rodenticides, and many infestations are safely and effectively controlled in this way. However, rodenticide use can represent a risk to non-target animals, and the emergence of 'hotspots' of resistance to anticoagulant rodenticides has led to concerns over the long-term viability of a rodenticide-biased approach. This study investigated some non-rodenticide approaches to rat control on farms. Small mammals potentially compete with rats for resources, and managing the habitat to encourage them could indirectly solve rat problems. Field margin surveys were conducted to examine the distribution of small mammals, and identify habitat characteristics that are associated with rat populations. The results were inconclusive, although there was some evidence that dense ground vegetation favours some small mammal species and discourages rat colonisation. In later trials, reducing cover and harbourage around farm buildings reduced rat activity and survival, and compared well with rodenticide use in terms of efficacy and labour input. By reducing cover around farm buildings, good results were achieved within a short space of time. However, the technique is likely to be more useful as part of a long term strategy, whereby greater consideration is given to making the farm environment less suitable for rats, without reducing the quality of the habitat for other species. It is unlikely that a resource management approach would not include the use of other methods, including limited use of traps and rodenticides where necessary. However, less emphasis on rodenticides could potentially offer long-term benefits in the form of reduced risks to non-target wildlife and help to limit the spread of resistant rat populations.