To my horror, but thanks to Dr. Gareth Morgan’s recent announcement that he will donate $5 to Bob Kerridge’s SPCA for every cat they euthanize rather than release, I discovered that some factions of the SPCA are releasing cats into our cities, towns and countryside – lots of cats. Bob Kerridge – CEO SPCA – is considered a hero by a few for it. They call it trap-neuter-release – TNR

But TNR is not a solution

TNR programs do not stop the cat problem because cat numbers can only decline when a cat dies. But more cats are abandoned and migrate into the colony from other places to replace those that die [1]. Indeed, the presence of TNR in a neighbourhood is likely to encourage some domestic cat owners to release and abandon their cats – knowing that they will be cared for. The problem, therefore, is not solved.

TNR is not a viable solution when stray and feral populations are large [2] like in our major cities and wilderness. Success depends on de-sexing the majority of the population and getting them before they breed. Achieving those capture rates is extraordinarily difficult. Cats try not to be caught. A proportion of cats will not be caught and continue to breed.

TNR of so many colonies and so many cats takes constant monitoring, coordination and extraordinary resources. When that investment is not achieved or periodically fails to be maintained, which is inevitable for most colonies some of the time, cat colonies recover and grow again.

The ‘cat lovers’ who care for stray and feral cat colonies are also unlikely to be motivated to push TNR colonies into decline and eventual disappearance, even if it were possible, because they would be out of a cause or out of a job. It is more likely that they will just manage colonies of stray and feral cats in perpetuity. Indeed, in programs around the world those TNR programs that do reduce colonies end up with many small managed colonies requiring on-going investment, not the removal of the stray and feral cat problem [3].

The few TNR programs that were reportedly successful were only small populations where adoption campaigns could also remove a large number. The capacity of the human population to absorb cats is limited. We already have one of the highest cat ownership rates in the world.

TNR protects disease and predators of our native wildlife

Disease and parasites are a major problem of stray cat colonies in cities. They vector diseases to other domestic pets and people, including toxoplasmosis – a disease carried by cats which infects 40% of New Zealanders at some time in their lives and cannot be cured.

De-sexed stray and feral cats continue to impact native wildlife and on a much greater scale than anyone imagined. Stray and feral cats cause the greatest harm because they hunt to survive.

TNR does not address the human health and native wildlife problems – stray and feral cats even de-sexed continue to carry and transmit disease and kill native wildlife. By managing colonies of stray and feral cats we are effectively maintaining a reservoir of infection, disease and native animal predators for the future – madness.

Bob! – take Morgan’s $5 – you will be doing New Zealand and New Zealanders a favour. If the SPCA doesn’t accept the offer they’re mad.

How mad? – see my next post.



1 Castillo, D. and Clarke, A.L. (2003) Trap/neuter/release methods ineffective in controlling domestic cat “colonies” on public lands. Natural Areas Journal 23, 247-253

2 Guttilla, D.A. and Stapp, P. (2010) Effects of sterilization on movements of feral cats at a wildland urban interface. Journal of Mammalogy 91, 482-489

3 Jongman, E. and Karlen, G. (1996) Trap, neuter and release programs for cats: A literature review on an alternative control method of feral cats in defined urban areas. In Urban Animal Management Conference Proceedings, pp. 81-84, Australian Institute of Animal Management Inc.