Ecological Management of Rodents

Introduction

The specific objective of this project was to strengthen the generation of appropriate, cost-effective and sustainable technologies for rodent pest management in small-scale farming for the SADC region. To do this, we carried out essential ecological research that is required to develop sustainable community-managed rodent pest control strategies. Many farmers will understand that rodents are a problem and damage their crops, stored food and personal possessions. However, awareness among farmers about the level and scope of damage is often underestimated. For example, rodents can transmit more than 60 different diseases, the symptoms of many may be confused with other diseases (e.g. malaria, dengue) where awareness is higher. It is, therefore, important to raise awareness and generate accurate information about the multiple damages caused by rodents, producing data that show true levels of loss and contamination, and disease risks. Providing people with the true cost of rodents on their livelihoods allows them to consider how much they can invest (traps, poisons, labour) in controlling rodents. The measurement of success also needs to be reflected through the same rodent damages to livelihoods (as opposed to simply counting the number of dead rodents). The way people interact with rodents can be complex (seeing them as food, pests, or even involved in witchcraft) so capturing people’s knowledge, attitudes and practices with regards to rodents will also be essential to improving the way in which rodent pests are managed.

Rodent Ecology

The international scientific community and rodent pest control industry increasingly recognise that rodenticide use, alone, is not an appropriate solution for rodent pest problems found in small-scale agricultural communities throughout Africa and Asia. As has occurred with insect management, an integrated approach for rodent pest management is increasingly viewed as more sustainable and cost-beneficial. However, such an approach to rodent management requires a good understanding about the rodent species, their behaviours, breeding potential and habitat use in a given area. Unfortunately, these factors are poorly understood for indigenous African rodent species and habitats throughout Africa. Ecologically-based rodent management can only be developed and applied through the generation of rodent ecology research within relevant contexts.

Rodent Impact Management

Although effective rodent control methods exist, their poor application and adaptation to particular situations often results in treatment failures, leading to apathy and widespread acceptance of rodent pests in the environment. Generally, there is a poor perception about the impact of rodents on people’s livelihoods which is partly due to their multiple impacts (agriculture and health), the difficulty to assess some of the problems (e.g. crop loss) and low public awareness (e.g. disease transmission) about the damage caused by rodents.

Current rodent control practices are often based on the use of rodenticides. Misuse of these poisons is unfortunately common in many SADC countries, which poses a threat to human health and environmental contamination by killing non-target species such as predatory birds and using highly dangerous poisons which are often banned. More importantly, misused rodenticides may not significantly reduce the rodent population, therefore having little impact on reducing the damage caused by rodents. When correctly used, rodenticides can be a highly effective tool, but they are most appropriate in large-scale, intensive, high-value situations where safety and accuracy can be assured. The success of anticoagulant rodenticide baits in controlling rodents in developed countries has inadvertently stifled research on other aspects of rodent behaviour and ecology that could help develop more sustainable methods of control in the small-scale agricultural situations found in Africa. Because rodenticides can be expensive and difficult to use safely, other rodent management methods involving trapping and environmental management are more appropriate for the rural agricultural situations found in Africa. However, there has been insufficient research to develop appropriate tools and strategies for rodent pest management for different agro-ecological conditions, particularly targeting small-scale farming.

Rodent-Human Interactions

Sylvatic rodents species do not generally come into contact with people and are generally not considered to be pests. Many of these species serve important ecological purposes (seed dispersal, predation) and may act as reservoirs for various zoonotic diseases. Agricultural expansion often disrupts and fragments wild habitats, causing increased competition over resources and increasing interaction with commensal rodents that migrate with expanding human-influenced habitats. Sylvatic species may, therefore, pass disease to commensal rodent species or come into increasing contact with humans by foraging in and around human settlements. The impact of agricultural expansion can have two major effects:

1. It puts people at greater risk of contracting zoonoses such as bubonic plague
2. It can drive sylvatic species locally extinct, replacing them with invasive commensal rodents such as Rattus rattus, thereby reducing biodiversity and ecological health. Evidence suggests endemic diseases such as plague are spreading, and there is global concern about new zoonoses emerging and expanding endemicity.

However, little research to understand these processes in Africa has been carried out, particularly with regard to the role of agriculture in facilitating zoonosis.