Can an unspayed cat really result in 420,000 cats in seven years?

Question: Can an unspayed cat really result in 420,000 cats in seven years?

I've seen those numbers bandied around, even on your site, but I'm finding it hard to believe. I wonder just how accurate those figures are, and what studies have been made to substantiate them.

Answer: I'm not sure who originally put together those figures, but you are right; they do appear all over the Web. And (meow culpa), I was taken in like a number of other well-meaning advocates, thinking that this was an excellent argument for spaying and neutering cats. Those numbers backfired, however, when opponents to TNR (Trap-Neuter-Return) started using the 420,000 figure as proof that TNR doesn't have a chance.

Fortunately, others also questioned the validity of this projection. The Feral Cat Project recently documented studies done by wildlife biologist Dr. Michael Stoskopf, and sent his findings to the University of Washington Math Department for analysis.

The results? A much more believable projection of 100 to 400 cats at the end of seven years. The difference, you see, is:

1. The original figure was based on one cat delivering 12 kittens a year, with a 20% mortality rate. Dr. Stoskopf ’s studies found six kittens a year, with a 75% mortality rate.
2. The original projection assumed 100% survival of all the cats grown to adulthood for the entire seven years, a percentage that should have triggered red flags from the very beginning.

For the complete story, please visit The Feral Cat Project site.

Although it doesn't give the instant shock value of the higher number, 100 more unwanted cats per whole female stray still forms the basis of a compelling argument for the spay and neuter of cats.