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Why killing doesn't work

Some cat management authorities imagine that trapping and destroying free-roaming cats will remove any cat-related problems. This method does not work, for several reasons:

  • The remaining cats will breed more successfully;
  • Other cats will move into the vacant territory;
  • Residents who oppose killing healthy cats will sabotage the scheme.
  • Vacant territories are quickly occupied

All animal populations are controlled by the resources available in their territory. If a population becomes too large for its food supply, the death rate will increase and the population will be reduced. So, if free-roaming cats are trapped and removed, more resources will be available for other cats, either kittens produced by the remaining felines or new cats moving into the territory.


UFAW has clearly explained why removing cats doesn't work (1):

"Total eradication of a colony is difficult, labour intensive, time-consuming and therefore expensive. Almost inevitably a few cats will avoid capture. Unless food sources are strictly controlled these survivors wil reproduce and re-form the colony. Even if eradication has been successful there is always a risk that other straying cats will move in if shelter and food is there to attract them. The food may be wild rodents or unsecured waste bins, or there may be cat feeders unknown to the owner of the land. Every site may be considered to have a carrying capacity for cats which will depend on food supplies and availability of shelter. If cats are there and can breed, the population will tend to increase to fill that capacity."

The food supply is almost impossible to control. A study of free-roaming cats in urban Baltimore USA concluded that food was easily available and hunting played only a minor role in their diet. Analysis of scats and a door-to-door survey of 430 households showed that these cats survived mainly on food either provided directly by humans or indirectly via garbage. The same results were also found in 4 other studies in the US, UK and Italy (4). What this means is:

  • free-roaming cats are not a danger to wildlife as claimed by some people;
  • there is plenty of food for colonies to re-form if cats are removed.
  • Trapping and removing has effects opposite to those intended.

There is more food available for kittens. "... trapping and disposal programs may in fact increase the survivability of kittens born into such colonies by increasing the number of vacancies in the ecologic niche." (5).

There are not enough cats left to defend the territory. New cats move in, the colony is unstable, and behaviour problems worsen. "... the repeated influx of new cats into the colony increases territorial and hierarchic fighting, increases the probability that new diseases will be introduced into the colony and generally exacerbates the very behavioural patterns for which feral cats are usualy labelled a nuisance. If population numbers could be stabilised and turnover could be reduced, territorial behaviour within the colony would discourage migration into the colony from outside, resulting in a group of cats that should be healthier, quieter, and more acceptable to their human neighbours."(5).

Any scheme based on trapping and removing cats has to be repeated about every 6 months, without actually solving the problem for cats or humans. (6)

"The high population of stray, lost or abandoned cats in urban areas soon moves in to fill the vacuum left by those destroyed and recolonizes the vacant area, at the same time refilling it with the associated feline problems. Need for control is then required once again. In London this vacuum-filling process seems to take 3-6 months, depending on the time of year."