A great debate has been raging for several years now about how to control the number of feral cats. On one side of the debate we have wildlife conservationists who argue that the domestic cat is an invasive species that is slaughtering native species and must be eradicated in the same way that other invasive species are eradicated – by killing them all. On the other side we have No Kill advocates who argue that trap-and-kill programs do not work and that feral cat numbers can be managed and gradually reduced by trap-neuter-return (TNR). The two sides have been battling for years, with wildlife biologists successfully opposing TNR in some places.
Underlying this debate is an assumption that has, as far as I can tell from reading the non-paywalled literature, never been addressed in any systematic way. That assumption is that feral cats in the United States are like other “invasive” species such as starlings and Burmese pythons, in that their numbers are rapidly increasing. We see projections that one feral cat can have hundreds of thousands of offspring in a few years, for example. The label “invasive” itself designates a non-native species that comes into an environment and takes over, squeezing out native species by its rapid reproduction. Think kudzu.
What do we know about feral cat population numbers in the United States? The most accurate answer to that question is “nothing.” Over the years various estimates of feral cat populations have been made, often in the range of 60 million. One recent study that attracted a lot of attention estimated that there were from 30 to 80 million un-owned domestic cats in the United States. This estimate was made in a 2013 article by Scott R. Loss, et al., published in the journal Nature Communications. It is often referred to as the Smithsonian study. The Smithsonian study did not report any original research on the number of un-owned cats in the United States; instead, it made estimates ostensibly based on five other studies. The authors of the paper acknowledged, however, that: “No precise estimate of the un-owned cat population exists for the United States . . . .” Because they had no good data on numbers of un-owned cats in the United States, they used data from other countries to estimate what the population might be in the United States. The wide range in this estimate, and the lack of data from the United States, resulted in numbers that I would characterize as “guessing.”
But in spite of the lack of data on the feral cat population nationwide, there are useful things we can say about feral cat distribution and their numbers over time. First of all, as to distribution, domestic cats are a commensal species, and as such their numbers are heavily dependent on the human population. As a commensal species, feral cats live primarily in the cities and suburbs. This is an extremely important fact about feral cats that has been given virtually no attention in connection with control measures. There is no evidence whatsoever that feral cats exist in sufficient numbers to cause damage to populations of native species in wild areas of the territorial United States, away from human habitation. Nor is there any evidence that feral cat numbers in wild areas are increasing. The commensal nature of the cat, and its dependence on its association with human habitation, means that feral cats are not an invasive species in the classic sense of over-running natural habitat and crowding out native species. Since feral cats require resources that they find in human habitations to reach high populations, efforts to control those populations must concentrate in cities and suburbs. We do not need to be concerned about most wild areas, because they have very few feral cats.
In the cities and suburbs where feral cats live, there is not a black-and-white line between feral and tame cats. Although feral and tame cats may be very different behaviorally, they are denizens of the same urban habitat and their populations intertwine. In many colonies you will find feral and tame cats living side-by-side. Therefore, what we are really interested in for purposes of designing control programs is the number of free-roaming cats (aka community cats), whether they are feral or tame.
The two important facts discussed above – that cats are commensal and that the population we are interested in for control purposes is free-roaming cats, point us to an important data source that has been completely overlooked in discussions about the feral cat “problem” – historical animal control data. That data shows us that the population of free-roaming cats in the urban areas where cats actually live has been plunging since the early 1900s. All we need to do to “control” the free-roaming cat population is to figure out what we have been doing right and do more of it.
Free-roaming cats were apparently not considered a problem in American cities until the latter half of the 19th century. In fact, there are references in historical documents to cat shortages. Large numbers of horses and dairy cows were stabled in cities throughout the 1800s, and you could find cats in every stable. Horses ate grain, and cats deterred rodents from getting to the expensive grain. It was not until around the end of the 19th century that the number of cats grew large enough in New York City, Boston, and other large cities that systematic efforts to control their numbers were made. In New York City, that job fell to the ASPCA.
The ASPCA has made their intake and euthanasia numbers available for selected years in the period from 1894, when they were awarded the responsibility for animal control in New York City, to 1994, when they gave up that responsibility. During that 100-year period, the vast majority of animals who were taken into shelters in the city were taken in by the ASPCA. The ASPCA is to be congratulated on their willingness to make this data available, because it is the sole source of shelter intake data that we have that goes back to the early 1900s.
The cat-intake numbers from the ASPCA official reports are astonishing. In 1895 the ASPCA took in 24,140 cats. That number rapidly went up as the ASPCA ramped up its animal control operation. In 1914 the intake number was 177,234, and in 1928 it was 217,774. In 1934 the cat intake number peaked at 219,506 cats. According to unofficial reports, the numbers in some years may have been even higher. One report was that the ASPCA killed 303,949 cats in 1911 (Forbush, The Domestic Cat). But the number of cats impounded by the ASPCA fell sharply from 1934 to 1946, and in 1946 the ASPCA impounded 155,312 cats. The decline continued, and in 1965 the number was 75,858. In 1994, the number was 27,366. The number of cats impounded in New York City continued to decline after the city took over animal control in 1994, and in 2014 cat intake was 18,784. Meanwhile, the human population of New York City increased from 5.6 million in 1920 to 8.5 million today.
If we pick 1920 as a base year and compare it to 2014, we see a dramatic fall in cat intake numbers in New York City, both in absolute numbers and numbers relative to the human population. The number of cats impounded by animal control fell from about 200,000 per year in 1920 to 18,784 in 2014. That is a decline of 91% in absolute numbers. The decline relative to human population was from 36 per 1000 people in 1920 to about 2 per 1000 people today, a 95% drop.
Now, some people (particularly wildlife biologists, I suspect) would criticize these numbers as meaningless. They would argue that the numbers are for only one city and that enforcement as to cats may have changed over the years. These are valid criticisms, but I do not think they invalidate the evidence of a plunge in free-roaming cat numbers.
As to the objection that the numbers are from only one city, we have quite a lot of national data showing a fall in shelter intake across the United States. This fall in intake has been particularly well-documented for the years 1970 to 2000. It is not the quality of data we would ideally like to have for scientific study, but it is consistent across a large number of shelters. Those estimates are that shelter intake nationwide, of cats and dogs, was some 26.5 million in 1970 and about 9 million in 2000. As to the objection that animal-control enforcement may have changed over the years, changes in enforcement up to at least the year 2000 were in the direction of more enforcement against cats, not less. And in any event, we are not looking at a subtle finding here. Plunges in the number of cats impounded on the order that we have seen in the United States is hardly likely to be solely due to changes in enforcement.
Additional evidence that the number of cats in cities has cratered comes from ecological studies that were done in the 1980s. Cat densities of from 725 to 1813 per square mile were found by researcher James Childs in Baltimore neighborhoods in the early 1980s. I am not aware of any more recent ecological surveys of cats in cities, but such numbers of free-roaming cats would surely be very rare in cities today.
So, what happened? Why did the number of free-roaming cats in our cities fall off a cliff? One thing that did not cause the decline in numbers was shelter killing. In spite of massive killing, the numbers of cats impounded in New York City throughout the early 1900s continued to rise. The explanation for the fall in the number of cats was changes in the environment. The great decline in cat intake that we saw in New York City from roughly 1920 to 1945 correlated with the period of time after horses and dairy cows disappeared from the cities. Cats lost their jobs protecting stables, and as the stables disappeared a huge chunk of the food and shelter resources that cats had relied on disappeared with them. Also in the early 1900s, cities began to make organized efforts to improve public health. In addition to getting livestock out of town, cities made big efforts to clean up the streets and get rid of abandoned buildings. Less trash in the streets and fewer abandoned buildings equaled fewer resources for free-roaming cats.
Another enormous change happened in the 1970s as safe, humane techniques for spaying and neutering were perfected and veterinarians began to recommend sterilization for owned pets as a routine part of healthcare. This trend accelerated in the 1990s as pediatric spay-neuter became accepted, and today a very high percentage of owned cats – estimates are over 90% – are sterilized. As more and more owned cats were sterilized, there was less and less seeding of the free-roaming cat population by owned pets. Another factor in the period from 1970 to 2000 was that residences began to secure their trash better. Photographs of Baltimore from the 1970s show alleys full of metal trash cans tipped over by dogs, with the lids scattered around. Today we have garbage cans with locking lids that are much harder for animals to open.
What part did TNR have in all this? TNR did not become widespread until recently, and it may be too early in the process to evaluate long-term effects of TNR on the population of cats in cities and suburbs. However, TNR should further decrease the seeding of the free-roaming cat population. If we could do TNR on a substantial percentage of the population of free-roaming cats in the cities and suburbs, we should see the same type of decline that we saw in feral dog populations from 1970 to 2000.
What more can we do? A 1989 paper by Calhoon and Haspell found that it was the availability of shelter that limited the number of cats in Brooklyn, and that supplemental feeding did not increase cat numbers. If we are serious about reducing the number of feral cats, we need to reduce urban blight, including getting rid of abandoned houses, garages, cars, etc. In the suburbs people must secure their outbuildings. TNR can help transition cats who are affected by these measures so that they can live out their lives in comfort. For example, when people complain about feral cats in their neighborhoods, we could trap, sterilize, and relocate the cats to a safe place, and then counsel the people to secure anything on their property that could potentially serve as shelter for cats.
But really, probably the best thing we can do is just relax. The trend in the number of free-roaming cats has been sharply down, and that trend is continuing. Since cats live mostly in the cities and suburbs, and since populations in those areas have been falling precipitously, we have a system that is actually working very well. We just need to be a little patient, and keep doing what we are doing.
The only thing that might slow us down is the bird conservationists. The bird conservationists see what we are doing as all wrong, and they want us to be forced to throw out everything we’ve worked hard for since 1970 and replace it with catch-and-kill programs. This reminds me of the people who advocate mandatory spay-neuter. Mandatory spay-neuter actually results in fewer animals being sterilized, because such rules drive people underground. Similarly, catch-and-kill programs will result in people hiding feral cats, and being afraid to reveal their presence to anyone. This will mean that fewer feral cats will be sterilized, thus setting back all our gains. Large numbers of feral cats live on private property, and the bird conservationists do not seem to realize that no government can give them the right to go on private property to kill feral cats.
The most effective way to protect our current success from the bird people may be to continue to grow our networks of feral cat caregivers. The reason the bird people have not succeeded so far in setting the clock back is that no mayor or city councilmember in his or her right mind is going to propose a mass extermination of cats. As long as our network is strong, that will continue to be the case. Wildlife conservationists have succeeded in derailing TNR efforts in some places, and that is a shame, but TNR, since it can be done by people on their own property, can exist even where formal programs are banned.
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