Discussion: The ‘vacuum effect’ and new cats replacing a removed colony of ferals

This article is a discussion on the ‘vacuum effect’ and feral cats. I invite those of you active (or retired) with real TNR (trap, neuter, return) experience to comment on whether your colony cats keep other cats run off, or, in the case of removed colonies, did new cats take their place.

TNR'ed and vaccinated feral cat gets rabies and bites person

Until September 7th I will give 10 cents to an animal charity for every comment written by visitors. It is a way visitors can contribute to animal welfare without much effort and no financial cost. Please comment. It helps this website too which at heart is about cat welfare.

Studies show removing feral cats from these areas creates a “vacuum effect”: Cats from neighboring areas move into the newly available space to take advantage of food and shelter. These cats soon begin to breed to capacity. Before long, just as many cats can be found in the area as were there before.

In a scientific study at Marion Island in the sub-Antartic over 19 years, scientists noticed that when cats were cleared from a preferred area of the island, cats from another area took their place.

There are plenty of articles and charts on the vacuum effect and feral cats online. I’d prefer to gather information from actual TNR trappers who understand the importance of not disturbing a settled feral colony if at all possible.

Do your neutered males keep new cats from joining? Have you dealt with the heartbreak of having to move a colony and watching new cats take their place?

Please sound off in the comments. Note: Cat-hating trolls will not pass comment moderation so don’t bother commenting.

4 thoughts on “Discussion: The ‘vacuum effect’ and new cats replacing a removed colony of ferals”

  1. The reason a colony inhabits a location is because it’s “desirable” for one reason or another. Therefore, to remove a colony from a desirable location leaves room for a new colony to take over that piece of prime real estate.

  2. The Vacuum-Effect really does exist. This short article discusses it. So many have thought it was a myth until they found more cats had replaced the original ones. Best to trap-neuter-vaccinate-return (TNVR) – its humane, effective and cost-efficient.

    Beth, president
    Community Cats United, Inc

  3. I started feeding/TNR 3 years ago, for a colony of 18 cats. I’ve fostered and adopted many of them out, yet I still have 18 cats. However, only 3 are “original”. No matter how many i find homes for, I always have 18 cats!

    • I’m surprised that many have been allowed to join the colony. I’ve watched neutered male cats run off strays who show up. It may take a few weeks for the newbie to get the message and not come back. Your colony must really love you Cindy 🙂


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