Feral Cats: Vacuum Effect

The so-called ‘vacuum effect’ in relation to feral cats is a reference to how feral cats repopulate an area which has been culled of feral cats because that particular area has a source of food which attracts the cats.

Feral cats
Feral cats. Picture in public domain.
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The whole situation turns on this fact: that feral cats occupy an area because there is a source of food. If you try to remove those cat through killing them and if the source of food remains then once again, over time, feral cats will repopulate the area because they are attracted by the food source. If you don’t kill all the feral cats then also the remaining cats will breed and repopulate the area.

The advantage of trap neuter return over simply killing cats is that it stabilises the population and indeed the population will decrease gradually if it is done comprehensively. And of course it is humane whereas the former method of simply killing cats can only be described as inhumane and ineffective.

Studies have demonstrated this. Alley Cat Allies refer to the removal of the entire population of feral cats from an island: Marion Island. It took 19 years of attrition against the feral cats using methods which would be unworkable in suburban areas. During the clearance cats from another area took their place thereby proving the point.

Cat haters, cat shooters and cat phobics (terrified of cats) hate the idea that the vacuum effect exists because they are very keen to see feral cats exterminated in any way possible and they hate TNR programs because for them it leaves cats on the ground where they can attack birds and other species of animal. Therefore cat haters will argue against the vacuum effect. They will say that it does not exist. They don’t substantiate their opinions with science. They are often ornithologists.

A more refined argument about killing feral cats would be to both kill them and remove the source of food at the same time. That would remove the cats from a particular area. But this is impractical and will never work. Sources of food are often businesses or indeed well-meaning people who voluntarily feed the cats. Other sources of food could be at harbours where there is fishing. You can’t remove businesses which is why the concept is impractical.

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6 thoughts on “Feral Cats: Vacuum Effect”

  1. To those who say just don’t put food out and the cats will stop coming don’t take into consideration the rodents in a given area. My colony has been very difficult to trap because they don’t really need me for food. At least once a week I see one of my colony cats walking by with a big rat in its mouth. If all of the feral cats are rounded up they’ll be replaced by more cats if the new cats know there’s plenty of rodents to chase, play with and finish off as a meal.

  2. I wish everyone who despised the sight of a feral cat would rail against the human race for perpetuating their existence because they allow intact cats to roam and breed and an acceptable method of getting rid of a cat still entrails opening the door and booting it out because ‘cats can take care of themselves’.

    As long as we refuse to address the absolute root of the problem the cats remain objectified as the source of the problem. They are just trying to survive.

    One thing I have heard from total idiots who don’t fix their pets is the fear they won’t be able to get another cat someday if we S/N as aggressively as needed to reduce the excess population. The same thing happened to horse breeders where thousands of horses were produced by major breeders for show and racing and smaller breeding programs. The excess found it’s way to the slaughterhouse. But the excess breeding meant the initial price of the horse itself low. Between the recession and education there are fewer horses available at higher prices but the purchase price is and always will be the cheapest part of owning a horse. I can’t believe that cats and dogs would rise to astronomical prices as there will always be available kittens and puppies. It is essentially impossible without some form of military action to forcibly S/N every pet on the planet.
    Possibly and it should be with the emphasis we have on pet ownership education in grade schools on responsible pet ownership should be taught in short seminars.
    I have argued before that whale hunting in Japan will not be stopped by Greenpeace or their offshoots but by the education of the coming generation. They are the ones that will shame their government out of ‘ scientific research’. Let the little children go home from school and shame their parents over that litter of puppies and kittens in the house.

    • I believe that we are gradually heading towards a time when there will be regulations about cat ownership. We can’t keep on taking cats for granted. We can’t keep on letting some, a minority, of cat owners being irresponsible about cat ownership. Something needs to be done. There need to be an educational program at least. I don’t know of any educational program concerning children and adults on cat ownership and neutering cats. I can’t see why it cannot be included in the school curriculum but it could include all pets because they are members of families and they are a major part of our lives. The bottom line is something needs to be done to tackle the root cause of the feral cat problem rather than constantly reacting to it. TNR is obviously a reaction to the feral cat problem. It is second-best to prevention.

      • Thank you Michael. TNR is a Band-Aid on human behaviors.
        I consider most adults I talk to as a lost cause if they don’t already see the problem. Our hope is to educate the coming generations.
        Dogs and cats are easy to get and easy to replace. Pet ownership is a choice and should come with the full responsibility that are laid out for dog owners.
        Overpopulation of dogs and cats has increased because of no-kill shelters but the numbers are increasing because it takes only a few nit-wits to repopulate an entire local population of feral and stray cats.
        Programs to kill, starve, poison stray and feral cats are no better than the negligent human who passed up the increasing availability of free S/N no matter what your income. We need to hit hard close to home where the source of the problem is.

        • I believe that the domestication of the cat and dog is, today, hardly a success. Some people would call it a failure. It needs to be changed I think quite fundamentally.


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