First observed by Roger Tabor, a world-wide renowned expert on felines,  in his studies of London's free-roaming cats (The Wild Life of the Domestic Cat). No feral colony is an island; it is surrounded by other feral cat groups in adjoining territories.
If a colony is removed but its food source remains, cats in neighboring territories will move in and start the cycle of reproduction again. Normally, most of these cats stay out of the territory if it is occupied by a colony of sufficient size.


Trap-Neuter-Return popularly known as TNR, is proving to be a very effective method at controlling the free-roaming cat population growth. The practice of TNR involves:


Trapping all or the majority of cats in a colony, with a non-lethal approach as a solution.


Spaying/neutering, vaccinating, and identifying them as altered by ear tipping or ear notching the left ear, and then returning them to their territory.


Ongoing support for a colony is given by a caregiver. Caregivers then monitor and provides shelter and supplies food and water. The colony is also monitored for new cats that may be accepted, so they too can be trapped and returned. When at all possible, kittens young enough to be socialized and friendly adults are removed and placed for adoption.


After at least 85% of a colony has been TNR'ed it will stabilize its size wth monitoring. 100% sterilization will show a gradual decline of the colony over time.


The Vacuum Effect

The Vacuum Effect

- Less nuisance behaviours such as cats yowling and noise that comes with fighting and mating activity.


- Reduction in the odor associated with unneutered males spraying to mark their territory.


- TNR'd cats also tend to roam less, therefore becoming less visible.


- TNR'd cats still continue to provide natural rodent abatement, a valuable benefit in urban areas.


- Spaying and neutering of ferals lowers the number of cats and kittens flowing off the streets into local shelters.


- The euthanasia rate for domestic cats drops when there are fewer ferals because the lack of street kittens means less competition for spots in adoptive homes and shelters.

TNR has the advantage of being humane because it respects the cats' right to live and provides them with as high a quality of life as possible under the circumstances. It is also effective at lowering population levels, both within individual colonies and across entire communities. Other methods not only cost more; they don't work. TNR is clearly the future when it comes to enlightened care of feral cats. - Neighborhood Cats, New York


In San Diego, after only two years of county-wide TNR, euthanasia of cats dropped by over 40 percent. In San Francisco, after six years of a citywide TNR program, the euthanasia rate for all cats, domestic and feral, dropped by over 70 percent.


One of the primary arguments in support of Trap-Neuter-Return is that it has proved to be, when implemented properly, the only method that has succeeded in controlling feral populations ongoing.  The traditional approach of trap and kill where feral cats are trapped then invariably euthanized has done nothing to alleviate the growing free-roaming cat population, and proof seems to be in the pudding when we look at the out of control feral cat numbers in most regions.


There are clear reasons as to why this method has failed in the past:


Difficulty in catching all the feral cats in a colony. Trapping can be very time consuming and requires a great deal of persistence.

​If only a few cats are trapped, then the remaining cats will overbreed to grow in size up to the number of cats the food source will allow.


If all the cats are trapped and removed in the colony, that still won't diminish colony numbers over the long-term. This is due to a phenomenon call the vacuum effect.


Unable to completely change the environment and remove all shelter and food sources, such as restaurant waste, household garbage, or cans of food that are left by cats' caregivers.

Failed Alternatives

Other Facts

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