I am Alexandre from the French association PAZ. Our association is dedicated to acting for animals by seeking concrete progress. We have various campaigns: end of wild animals in circuses, end of live fishing, awareness campaigns... We also chose to act for the so-called “liminal” animals following the book Zoopolis by Sue Donaldson and Will Kimlicka: liminal animals are those animals that are neither wild nor domesticated and that live in human spaces, near us. Pigeons, rats or rabbits are thus liminal animals at our side.

We have a strong understanding of the issues of effective altruism and wish to strive for the greatest effectiveness in our areas of expertise. We believe that when considering liminal animals, the number of animals involved, particularly rats and fish, merits attention in discovering the best ways to act on their behalf. For example, we would like to launch a campaign for rats in Paris, whose numbers are estimated to be in the millions. The Paris City Council is engaged in a fight against rats and uses anticoagulants that cause internal bleeding or alcohol traps in which the rats drown to control their populations.

We would like to act, because we believe we have established strong links with politicians: some of them are likely to want to act in favor of rats. We got a large media coverage about rats suffering. And according to our Paris inhabitants polls, 61% want non letal solutions for rats. Unfortunately, we are blocked by a lack of knowledge: we do not know precisely how many rats there are and what non-lethal methods of rat population control could be used.

We would like to highlight effective non-lethal methods:

- we should act upstream, in the urban space, by limiting reproduction. We would like to have an estimate of the cost of surgical contraception (it doesn’t seem cost-effective a priori but we would like to have an estimate in order to decide). We would like to know if an oral contraceptive exists and if it is effective in an urban space, where rats are likely to eat anything other than what the contraceptives are encapsulated in. We would like to know the differences in impact whether the rat is a female or a male, the environmental consequences the contraceptive could have via urine, and better define the regulatory issues. For example, hormone-based contraceptives, such as Contrapest, are banned in Europe.

- Urban planning should also be addressed: which garbage cans can limit access to waste, which plants in parks and gardens could have an impact...

We would like to discuss the opportunity to obtain this information by financing scientific research. We do not have the scientific knowledge, the experience in conducting scientific research, or the funds to do it: it seems like a daunting task and we are not the best people to do it. However, we would like to initiate a process of reflection on the opportunity of research on these issues. If there are several million rats in Paris, then it seems reasonable to think that there are billions of rats in cities around the world. Such research seems promising.

I would like to get your opinion on this problem, on its tractability and on possible next steps. I will be at the EA Global: feel free to come and see me or contact me on Swapcard.


Alexandre Mouchel
Campaign Manager – PAZ
alexandre [at] zoopolis.fr


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Hi Alexandre,

Great to hear that you are interested in rat welfare!


we do not know precisely how many rats there are

Have a look here where I give my rough estimate for the average urban rat population density.


For example, hormone-based contraceptives, such as Contrapest, are banned in Europe.

I think this is a big issue. The fact that ContraPest isn't available in Europe despite SenesTech's apparent intentions likely has something to do with the slow, complicated, and expensive process of getting approval for new chemicals/drugs in the EU. (I'm mainly basing this on conversations I've had with people at Innolytics, the producers of OvoControl).


You may also find the discussion of welfare implications of rodenticides in this report by Kim Cuddington at Rethink Priorities useful. The section "Rodents" under "Welfare implications" is the most relevant.

I’d recommend looking into Chicago - they distribute free rat-proof garbage bins for residents. 

Also in Chicago, there is a working cat program to deter rodents, run by Treehouse Humane Society. Sterilized feral cats are placed in an area with nuisance rodents. They acclimate in a cage for 2-3 weeks, then are released. During the acclimation period, rodents will smell the cat and start to relocate, likely to move completely once the cats are released.

This is slightly different than this thread, because these working cats are feral. They aren’t adoptable due to behavior; therefore, releasing them outside is their only live outcome. It would be difficult to get a collar on these cats unless they are under anesthesia. 

Community cat advocates argue that since the cats are sterilized and fed periodically, their predatory drive is significantly reduced, when compared to unsterilized and unfed feral cats who are doing the most harm to the bird/mammal populations. Since they are feral, they are more likely to stay hidden and are less likely to be a nuisance than a friendly outdoor pet. 14% of US households admit to feeding outside cats. 

Here are a few considerations which make this invention complex: 

  • The cats need to be fed by humans periodically. If they aren’t fed, they hunt and/or migrate. 
  • The acclimation process is laborious. If it is skipped, I’d say the cats have <50% likelihood of sticking around. 
  • These cats are feral; therefore, it is difficult to recapture them for re-vaccinations. Vets have hinted that the rabies vaccine is actually effective for much longer than the 1-3 year timeframe, and I don’t know if there is publicly-available research to confirm or deny. 
  • Not everyone likes cats, especially ones that are free-roaming outside. There are dozens of complaint types, which can include allergies, cultural aversions, misinformation, etc.
  • This is likely to be more well-received by the public if there is also a cat overpopulation issue (But if you need cats, I promise you there are plenty to go around) 
  • I’m sure there are many others, these just came to mind.

I have firsthand experience with the implementation in field, having run a working cat program in a rural area. If you’d like more information, please reach out! 

Hey Alexandre,  just wanted to note that ContraPest is not hormone-based, although it's true it has not gone through the regulatory approval process in Europe yet.