Rodents are found almost everywhere in the world. Their cohabitation with humans sometimes causes economic and health problems, as they can eat crops, damage infrastructure, and transmit zoonotic diseases. There are several ways to deal with these problems, such as adapting infrastructure with appropriate materials or conducting vaccination campaigns against specific zoonoses. However, the most common approach is to regulate their populations. 

Lethal methods are often used to achieve this, ranging from poisoning to trapping. Unfortunately, these methods are sometimes ineffective, dangerous to non-target animals and the environment, and, of course, cause immense suffering and death. 

To avoid this, non-lethal methods are increasingly being developed and used, partly because they seem to be more acceptable to the public. One of the most promising of these methods is to reduce the fertility of rodents, usually with oral contraceptives. The idea is that, by reducing rodent birth rates, their population size is reduced over time, thereby reducing their economic and health impacts.

The purpose of this article is to help researchers develop such methods by proposing a framework. The guide lists the important steps to follow and the data to collect to ensure the efficacy and safety of the contraceptive. It also helps researchers avoid embarking on such a project without a clear idea of the work required to bring it to fruition. 

The first step in such a project is to have an idea for a contraceptive product to be tested in a specific species, which requires preliminary research. In addition, it may be important to determine public opinion on fertility control methods, especially if the target species is in a limited region. For example, if the local farmers are all against such methods and prefer lethal methods, it might be necessary to try to change their minds first, at the risk that no one will use the product once it’s developed. 

Once this stage is completed, the framework lists a series of essential steps in the form of questions divided into three categories: captive studies, field studies, and modeling studies. These three categories are presented sequentially, with captive studies coming before field studies. However, some questions may be addressed in parallel. 

The steps are outlined below. To get a clearer idea of the guide and how each question is asked, the article itself contains more comprehensive information, provides a brief summary of the literature on the subject, and outlines the steps to follow in the event of a problem. For example, if the duration of the product is too short to be effective in the field, different doses and frequencies could be tested.

In captive studies, researchers should test:

1. The efficacy of the contraceptive, including its duration and differential effect on males and females. 
2. The safety of the product, ensuring that its side effects don’t compromise the well-being of the target animals. 
3. Ensuring that the bait doesn’t alter the effect of the contraceptive.
4. The compatibility between product duration and field requirements. 
5. The palatability of the product to the target species. 
6. The impact of the product on non-target species and the environment, minimizing any collateral effects. 
7. The effect of environmental conditions on the efficacy of the product.
8. The presence of a marker for the target species. This is usually an organic compound that tracks product consumption. 

In field studies with wild populations of the target species, researchers should test: 

1. The efficacy of the contraceptive with respect to the regulatory objectives. 
2. The effect of the product on the organism and behavior of the target species.
3. Whether the contraceptive can be properly delivered to individuals of the target species. 
4. The consumption of the product by non-target species and how this can be avoided.
5. The effectiveness of the product in reducing the birth rate and damage caused by rodents. 
6. The financial and environmental costs of using the product. 

Finally, in mathematical models, researchers should test:

1. The feasibility of achieving regulatory objectives within a given time frame.
2. The balance between implementation costs and benefits. 
3. Whether the product can be used in conjunction with other methods to achieve regulatory objectives. 

Once this third phase is complete, further field studies can validate the mathematical models before moving on to real-world applications. 

Although this framework can facilitate the development of effective rodent contraceptives, much of the work to support such projects doesn’t come from researchers. The political will to use and invest in non-lethal methods depends heavily on pressure from citizens to demand more ethical methods. But for this to happen, citizens need to know that they exist, which is not often the case. Animal advocates can therefore continue to educate on the issue, showing that it’s possible to regulate animals without killing them, and that this is above all a political choice.