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Feral Cats: The Real Dangers Of Letting This Problem Go Unchecked

The burgeoning number of feral cats in almost every community in the United States mandates that leaders in animal welfare and protection admit the limitations of TNR (Trap/Neuter/Release) as a cure for an epidemic of irresponsibility and accept a mandate to change how we think about and address feral cat overpopulation.

As a nation, we treat cats as disposable pets—failing to demand that they are licensed and microchipped to establish owner responsibility. We classify them as free-roaming (a throwback to the days when cats were kept mainly to kill rodents) and praise TNR cat colonies, giving the uneducated or naïve owner the impression that an outdoor life is natural and acceptable for a domestic cat.

There are few major campaigns that saturate the media before the springtime “kitten season,” directly targeting cat owners with spay/neuter messages. Then we wring our hands and lament that, when pet cats reach breeding age (4 to 6 months) and display undesirable mating behavior, they are placed outside, begin reproducing and are often forgotten or abandoned—and, if they survive, they become feral.


“Antioch is overrun with feral cats,” writes Nate Gartrell of the northern California Bay Area News Group in a Dec. 26, 2014, article, "Antioch Feral Cat Feeding Ban Proves Futile."  Antioch is a suburb of San Francisco.

“For years, hundreds of these free-roaming cats have permeated the city…,” Gartrell observes, “and volunteers from various homeless animal rescue groups have trapped and neutered hundreds of them as a form of population control.”

On the other side of the country, a New Jersey Neighborhood Cats group posted a desperate plea for donations to a TNR campaign on in August, stating, “Waldo, Junior and Ellie-Mae are waiting for your help…”

The requester describes how the three named cats live in a feral cat colony in Jersey City and a caretaker has been doing her best to spay/neuter when she can afford to make the trip to a veterinarian. “But kittens kept arriving," she explains, “and the small colony of five doubled in size, then doubled again….Today there are 40 ‘teenagers’ and adult cats and about 10 baby kittens in the colony.”


“According to the Humane Society of the United States, there are more than 70 million feral and stray cats roaming the streets,” an Animal Planet post tells us. And, because of the greater danger of diseases carried by stray and feral cats, “…the best thing that you can do to protect your domesticated cat against serious illness is to keep it indoors.” 

This site, “5 Most Dangerous Cat Diseases,” provides an excellent guide to the most common serious and often fatal diseases to which outdoor cats are susceptible, including Feline Leukemia, FIV, Feline panleukopenia (distemper), renal failure, and rabies. It also reminds us of the suffering of feral cats infested with fleas and parasites. 

We cannot ignore the potential impact of free-roaming feral cats on humans. Drs. E. Fuller Torrey and Robert H. Yolken contend that “cat poop could be a ‘vast and underappreciated’ public health problem.” They published a paper in the journal Trends in Parasitology in 2013 on the dangers of Toxoplasma oocysts found in cat poop.  They warn that “a single infected cat can deposit millions of oocysts, each of which may survive in moist soil for 18 months.


In a September 2004 article, "U.S. Faces Growing Feral Cat Problem,” National Geographic takes a realistic look at the impact of millions of feral cats on the environment, and states that, “[S]ome experts estimate that each year domestic and feral cats kill hundreds of millions of birds, and more than a billion small mammals, such as rabbits, squirrels, and chipmunks.”

Ron Jurek, a wildlife biologist for the California Department of Fish and Game, discusses the impact of feral and free-roaming cats, and estimates, ”In urban areas there are hundreds of cats per square mile—more cats than nature can support.”

National Geographic acknowledges the good intentions of TNR, stating, “Thousands of volunteers and animal welfare groups throughout the country stepped forward in the early 1990s to control the wild cat population through mass sterilization programs.”

Drs. Torrey and Yolken told CNN that studies in California have shown that cats deposit an estimated 1.2 million tons of cat poop into the environment each year.


Two experts have written why TNR, alone, can never be successful in resolving the overpopulation of feral cats on a wide-scale basis. It is not from a lack of funding or dedication by the “intrepid trappers,” as Dr. W. Marvin Mackie calls TNR devotees.  Rather it is the reality of the escalating births.


W. Marvin Mackie, DVM, founder/director of two Animal Birth Control spay/neuter clinics in Los Angeles County, was a pioneer in early-age spay/neuter and trained veterinarians worldwide in techniques he called, “QuickSpay.” During his long career, he was devoted to sterilizing feral cats and kittens.

Dr. Mackie shared his thoughts in the following personal interview, an expanded version of which appeared in the Pet Press, March-April, 2003:

I was inspired in 2002 by an article by Merritt Clifton [now editor of Animals24/], who discussed the application of the Fibonacci 70% rule to spay/neuter of dogs and cats,” Dr. Mackie explained.

“I realized that this concept is amazingly insightful into success or failure as it relates to ultimate pet overpopulation and deserves to be understood by all who are decision makers in the effort to bring it under control,” he continued.

 “Leonardo Fibonacci, a preeminent mathematician of his time, created a formula (model) in the early 1200’s relating to agriculture productivity. Six centuries later, Louis Pasteur, while working on an early vaccine for disease prevention, used the model to predict that 70% of a susceptible population would have to be vaccinated in order to prevent an epidemic of almost any contagious disease.

 “Fibonacci’s 70% model is still recognized as valid by leading public health authorities such as the World Health Organization and the Center for Disease Control.

“It is not a great leap to advance to the notion that pet sterilization is in effect “vaccinating” against the disease of overpopulation. Using this premise, we can say that 70% of the susceptible population (animalswith outside privileges) in a defined demographic area must be sterile in order to affect the decrease in over-birthing that will result in a population decrease within that area. 

“The outcome at this 70% sterilization level is that the transmission odds (successful breeding encounters) of the remaining 30% are reduced to the point that births then occur at a rate only great enough to replace normal attrition.

"If we follow the logical conclusions of the 70% rule, which is broadly accepted by those who work in epidemiology, we arrive at some interesting answers. For instance, those working so diligently to control pet overpopulation in the greater Los Angeles and Orange county areas are confounded by the fact that, in spite of their tireless efforts, they have not seen the hoped for reduction in euthanasias.

“Unfortunately, the fertile pet population was so large at the onset and the densely populated two-county area was so great that they were unable to sterilize the numbers required to reach the 70% mark. Mr. Clifton, states emphatically that you must reach 70% or FLUNK – there is no progress made with a “B” or “C” grade! 

“Clearly, the 70% rule applies to any circumscribed area. It can be an isolated town or the mere area of a feral cat colony. Generally, more affluent areas can and do reach 70% (or better) pet sterilization and the over-birthing problem ends in those areas. 

“The more impoverished areas don’t come close to 70% and the shelters serving those communities are the recipients of the hapless victims of too many births and too few homes.”

A similar position is presented in an excerpt from comments by Dr. Travis Longcore, Science Director, The Urban Wildlands Group, on the Initial Study/Draft Mitigated Negative Declaration for Proposed City of Los Angeles Citywide Cat Program, November 4, 2013. The following is provided with his permission:

“Even though current spay/neuter resources are effective at reducing the number of unwanted owned cats, switching those resources to feral cats would not be similarly effective at controlling overall feral cat numbers. Although this seems counterintuitive, it is a fact well established in the scientific literature. This derives primarily from the difference in sterilization rates in the two groups (owned vs. unowned).

“Owned cats have a high sterilization rate, high enough for sterilization to make a difference in the number of unwanted litters. If a cat population has an 80% spay/neuter rate, increasing the rate to 81% will further control population growth. That is, even a 1% increase matters.

“Unowned cats have a very low sterilization rate (< 5%), even in large-scale long-term TNR programs (Foley et al. 2005). Because of the significant reproductive capabilities of cats and the mobility of unowned cats across the landscape, the rate of sterilization for females has to be in the neighborhood of 70–90% for the sterilization to make any difference in the population growth rate (Andersen et al. 2004, Foley et al. 2005, Schmidt et al. 2009, McCarthy et al. 2013).

“At sterilization rates < 70–90%, increased reproduction from intact females makes up for the sterilized cats. If a cat population has a 3% spay/neuter rate, additional sterilization to a 4% rate will make absolutely no difference in controlling the population.

“Therefore, because owned cats already have a high sterilization rate, the additional effort to increase sterilization does influence the number of unwanted kittens being born, which is what the Los Angeles spay/neuter programs have been doing. Those same sterilization funds spent on feral cats, which generally have a < 5% sterilization rate, even with large-scale and long-term TNR programs (Foley et al. 2005), would be wasted.”


We cannot expect to achieve a complete absence of feral cats in a diverse, democratic country. However, by seriously applying the 70% Rule to spaying and neutering, and combining it with licensing, microchipping and a serious attitude toward the responsibilities of cat ownership—including keeping them indoors--the problems and suffering could be dramatically reduced. Cats deserve more from us than a life, and death, in the streets!

Sources: Santa Cruz Sentinel, You Caring, Animal Planet, CNN, National Geographic, QuickSpay

Photo Credit: Provided, Wikimedia Commons


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