Feral Kitten, Red River, New Mexico, USA - Photo Oakley Boren (Flickr)
19th August 2010: The question, "How fast do cats breed?" is a bit of a news story. I refer to Christie Keith's excellent story, Damn lies and cat statistics in the San Francisco Chronicle of the 18th August 2010. For some time a surprising statistic has been bandied about the internet (as frequently happens) that a single unspayed female domestic cat if left to breed in an unrestricted manner will lead to 420,000 offspring in 5 years. For the sake of accuracy Christie Keith says that the statistic states, "The offspring of a single unspayed cat will, within five years, add up to 420,000 cats."
The About.com website's cat section author, Franny Syufy, also asks the question: "Can an unspayed cat really result in 420,000 cats in seven years?"
You can see right away how things get changed when passed along the internet. Franny mentions a period of seven years and Christie refers to five years - no criticism intended.
Both authors rightly say that the figure is incorrect - dramatically so. Christie comes up with a figure of "98 and a high of 5,000 cats in seven years". While Franny says that a projection of 100 to 400 cats at the end of seven years is more accurate.
The stark differences are due to factoring in realistic survival rates as opposed to the perfect breeding scenario. If the survival rate of offspring is 25% rather then 80% then the figure tumbles to the much lower and more realistic numbers.
The sad thing about this story is that authoritative websites and organizations have used the incorrect figure to the detriment of the cat. It encouraged nasty people to brutally shoot the feral cat for pleasure and bird conservationists to demand a more vigorous extermination or control of feral cats. It also supported the skeptics of TNR programs as proof of failure.
Interestingly, it seems that the figure of 420,000 was exaggerated even when calculated on a theoretical basis. Dr Desmond Morris in his excellent book Catwatching published in 1986 addresses the issue of how fast do cats breed.
Dr Morris says that the domestic cat "may produce an average of four to five kittens in each of their annual three litters." He goes on to say that if we start with a single breeding pair of domestic cats, allow for fourteen kittens per year, the total after five years based on simple mathematics is 65,536. From that theoretical figure there has to be deductions for less than 100% survival rates, that males and females are not born in equal numbers and that cats don't all start breeding when a year old (in fact female cats start breeding at a younger age which would push the figure up).
It would seem that the major reducing factor is low survival rates of feral cats and kittens. Other factors include: he suggests that more than 90% of male domestic cats are neutered. There are also the TNR programs that have a reducing impact. And people who aren't formal cat breeders who allow their cats to breed may have kittens killed by their vet to reduce litter sizes (I am not sure about this last point).
In short there are many mitigating factors that reduce the numbers of offspring. The greatest problem that has been highlighted from this story is that we must be cautious in using the internet when searching for so called "facts". Assumptions should not be made even when the source seems fine. Sources should always be noted and often the best source is a book or research study. A study will at least quote true facts and opinion and divide the two.
I endeavor at all times to adhere to what I advise.
Note: the European wildcat has a single litter each year and an average of two to four kittens per litter (source: Catwatching)
How Fast Do Cats Breed? -- Related pages: