Indirect intervention

Although they may be costly, measures to prevent the ingress of rodents into buildings provide a long-term solution to rodent problems and are usually without adverse impacts. These measures should always be implemented, preferably before rodent infestations become established. Exclusion precautions are effective only if they are regularly inspected and operations at protected sites are adapted to accommodate them. However, some rodents and in particular house mice may be extremely difficult to exclude from the built environment because of their ability to penetrate very narrow apertures. Consideration should always be given to proofing premises at the conclusion of successful rodent removal operations in order to prevent infestations recurring.

Mice may be brought into otherwise secure premises in freight containers. Therefore precautions must be taken, such as thorough examination of goods coming into stores, to avoid failure of proofing measures caused by this.

A specific aspect of exclusion is the use of repelling machines. These may be based on electromagnetism, ultrasound and other acoustic mechanisms. There is very little scientific evidence from independent testing that these devices provide any significant effects on rodent behaviour under practical conditions. The same applies to repellent chemicals. Although attempts have been made to develop such chemicals, no scientific evidence is available that any shows sustainable effects.

Operations intended to prevent rodent access to foodstuff, such as the use of rodent-proof bins and close-fitting doors, are also likely to be substantially free from non-target impacts, although of course such action will also prevent access to any other animals, such as wild birds, that also may be relying on these food and water sources.

In order to deter rodent infestations, sites should be cleared of all debris, rubbish, old machinery and equipment, unwanted stores of straw and hay, etc. Vegetation should be cleared around buildings to provide an open perimeter and immediate surroundings, so that natural predators can take rodents. If possible, areas around buildings should be laid to concrete, or other hard surfaces, to prevent rodent burrowing. Once again, the only non-target impacts of such operations will be on the other animals that rely on the materials taken away for cover and harbourage.