Roadkills of cats fall 90% in 10 years –are feral cats on their way out?
From ANIMAL PEOPLE, November 2003:
BALTIMORE, SALT LAKE CITY, MENTOR (Ohio)–Is the U.S. outdoor cat population down 90% since 1992?
The feral cat population might be.
Roadkills of cats appear to have fallen 90% in 10 years, after apparently rising sixfold while the pet cat population nearly doubled during the 1980s.
An eightfold surge in the population of feral cats, mostly descended from abandoned and free-roaming pets, probably accounted for about two-thirds of the roadkill increase during the 1980s, but the trend is now completely reversed.
Current indications are that without continuing replenishment from wandering pet cats, the fast-falling feral cat population would probably stabilize at a thinly distributed level resembling the norms for other small felines such as bobcats, lynx, and caracal.
The large suburban feral cat colonies seen in recent decades may be an anomaly made possible only by the extirpation of street dogs and the temporary absence of native predators capable of eating either rodents or cats. Only in high-rise communities like Hong Kong and inner cities ringed by miles of pavement, like the oldest part of Rome, are large cat colonies likely to persist–and then only if humans supply enough food to sustain them.
Roadkill counts are among the sources of animal population data considered most reliable by wildlife biologists. Roadkill counts cannot tell in isolation how many animals are at large, but roadkills tend to be a relatively constant source of mortality as a percentage of the total number of deaths within a species, since the volume of traffic, exposure of species to roadways, and the behavior of the species around vehicles all tend to be consistent from year to year.
If roadkills of any species rise or fall, it is usually safe to suggest that the species is increasing or declining proportionately.
The American Journal of Veterinary Research in 1986 published a study by James E. Childs and Lloyd Ross which found that from 1978 through 1980 the city of Baltimore, Maryland, picked up an average of 2,721 roadkilled cats per year. At least 20%, Childs and Ross believed, were pets or former pets.
That was the earliest comprehensive count of roadkilled cats known to ANIMAL PEOPLE. Since many studies indicate that both the U.S. pet cat and feral cat populations tend to mirror human population distribution, and Baltimore lies close to the climatic midpoint for the U.S. as a whole, the Baltimore ratio of one roadkilled cat per 270 residents can be projected to the nation with reasonable hope of accuracy.
The U.S. had 226 million residents according to the 1980 census, and thus probably had about 839,000 roadkilled cats.
The Baltimore data can also be compared to the 2000-2003 roadkill toll in Salt Lake County, Utah, of one cat per 488 residents, published on October 14 by Deseret News reporter Lynn Arave.
Salt Lake County in recent years is actually much more representative of the U.S. as a whole than Baltimore was in 1979-1980, offering a good balance of both habitat types and income strata. The Salt Lake County data, projected to the total current U.S. population of 281 million, would indicate a current national roadkill toll of 577,000 cats–a drop of only about a third since 1980.
The drop is still significant, considering the increase in the U.S. pet cat population from circa 38 million to 73 million during the same years. The 32% decline in roadkilled cats points toward a steep reduction in the numbers of outdoor cats, including both free-roaming pets and ferals.
But there is still better news for workers against pet overpopulation and outdoor cat proliferation–because there would have been much worse news circa 1992, if anyone had then assembled the roadkill data.
Data gathered by ANIMAL PEOPLE from sources including surveys of cat rescuers in 1992 and 1996, the annual Dr. Splatt roadkill counts directed since 1992 by Brewster Bartlett of Pinkerton Academy in Derry, New Hampshire, and the monthly tabulations of roadkilled cats kept since 1993 by Mentor, Ohio municipal transportation department employee Cathy Strah, indicate that in the early 1990s the number of roadkilled cats nearly equaled the numbers killed in shelters, at about 5.4 million per year.
The neuter/return technique of controlling feral cat numbers was introduced to the U.S. in a big way during the early 1990s, chiefly through the 1991 formation of the national advocacy organization Alley Cat Allies and a heavily publicized experimental neuter/return project undertaken by ANIMAL PEOPLE in northern Fairfield County, Connecticut.
By 1996 the indicators that had pointed toward a U.S. roadkill toll of 5.4 million cats per year were suggesting that it had fallen back to about 2.4 million, even though roadkills had become almost three times as significant a source of mortality among feral cats. Shelter killing had dropped in importance by half, along with other human-caused mortality including poisoning, shooting, and captures by fur trappers.
As neuter/return continued to gain popularity, the roadkill toll on cats continued to fall at a comparable rate. In Mentor, for example, the number of roadkilled cats relative to residents fell by more than 50% from 1993-1996 to 2000-2002.
What that means is best illustrated with a graph:
Shelter killing = S (dogs & cats)
Cats killed in shelters = C
Roadkilled cats = R
Predation = P (italics indicate hypothetical trajectory)
Year / Millions killed
20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 .5
80 S 16 to 20 million pet cats (40%-50%) roam. R p
81 s C r p
82 s r p
83 s r p
84 s r p
85 S r p
86 s r p
87 S r p
88 S r p
89 S r p
90 S r p
91 S r p
92 Up to 28 million (50%) pet cats roam. S r p
93 S R P
94 s r p
95 s r p
96 s RP
97 S p r
98 s p r
99 sp r
00 p S r
01 p S r
02 Up to 24 m. (33%) pet cats roam. p S C R
20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 .5
The capital letters in the graph represent the years for which ANIMAL PEOPLE has actual survey data. The lower case letters provide the implied trajectory of the data during the remaining years. The italicized lower case letters represent a hypothetical projection of predation on outdoor cats, in absence of any data previous to 1992.
The shelter killing tolls plotted on the graph are taken from surveys done by the American Humane Association until 1992, and from data collected and analyzed by ANIMAL PEOPLE for subsequent years.
About two-thirds of the animals killed in shelters circa 1980 were dogs. By 1990 about half were cats. Today up to two-thirds are cats; more in some regions.
The effect of subtracting dogs from the shelter killing toll , as indicated by the “C” axis, is to move the lines of descent in recent shelter killing and roadkills into near parallel.
The three major factors in the apparent steep decline in roadkills of cats since 1992 appear to be that fewer pet cats roam; feral cat fecundity has collapsed to substantially less than the replacement level; and predation on outdoor cats by native wildlife has approximately tripled since 1996.
As of 1980, James E. Childs discovered in a study published by Anthrozoos (Volume III, #4), approximately 42% of Baltimore cat-keepers permitted their cats to go out. The cats who went out spent up to 45% of their time outside, meaning that pet cats who went outdoors may have had no more than 45% as great a likelihood as feral cats of being roadkilled, picked up by animal control, or killed by wild predators.
As many as half of all catkeepers still allow their cats to roam, Carol Fiore of the Wichita State University Department of Biological Sciences found in a 1999 survey of Wichita catkeepers.
However, catkeepers whose cats do not roam now have from two to three times as many cats, a trend that in hindsight can be seen developing in Childs’ data even though he did not directly remark on it. This reflects the much higher mortality among outdoor cats, which appears to be from two to three times greater than among cats who are kept indoors.
ANIMAL PEOPLE affirmed the higher mortality among outdoor cats in a 1992 survey of about 170 feral cat rescuers, who supplied data pertaining to the deaths of 2,638 cats in all. Half were killed in shelters; 10%, or 20% of those not killed in shelters, were roadkilled. Predation by coyotes, foxes, fishers, badgers, hawks, owls, eagles, and alligators was noted, but appeared to claim no more than 4% of the cats.
In 1996 a follow-up survey of about 60 feral cat rescuers produced data pertaining to the deaths of 361 outdoor cats. About 25% were killed in shelters, only half as many as four years earlier, but 28% were roadkilled and 9% were killed by predators.
If roadkill mortality among outdoor cats in 1980 was about 10% of total mortality, as in 1992, total outdoor cat mortality was about 8.4 million. Shelter killing probably accounted for half, also as in 1992, with surrenders of unwanted litters from pet cats accounting for most of the remainder of the eight million-plus cats who were killed in shelters.
If feral cats survived an average of one year, while pet cats who were allowed outside lasted an average of three years, as indicated in Childs’ 1978-1980 data, the U.S. population of true ferals as opposed to roaming pets and strays might have been as low as three million–but it was about to explode.
Among the pet cats allowed outdoors, as few as 26% were sterilized according to one northern California study, although another northern California study done at about the same time found that 58% of pet cats were sterilized overall. Childs found two years later that 62% of the pet cats in Baltimore were sterilized.
Even the most conservative projection indicates that at least 10 million cats–and perhaps twice as many–were at large and breeding in 1980.
The gradual removal of free-roaming dogs from U.S. cities and suburbs during the 1960s and 1970s had meanwhile opened habitat and food sources to feral cats at a possible biomass replacement ratio of about three cats able to survive in place of each dog.
By 1992 the U.S. pet cat population was already two-thirds larger than in 1973 and about one third larger than in 1980. Possibly half were still roaming at large; perhaps half of those were breeding.
If 10% of the free-roaming cats were roadkilled, as the 1992 ANIMAL PEOPLE survey indicated, the 1992 national toll included about 2.8 million pet cats and 2.6 million feral cats, for a total of 5.4 million.
This neatly coincides with the 1992 ANIMAL PEOPLE projection that up to 40% of the total U.S. cat population at that time were feral, including approximately 26 million adult feral cats, rising to 40 million during the spring/summer “kitten season.”
This is probably when the U.S. feral and outdoor pet cat populations both peaked, even as sterilization of pet cats rose and shelter surrenders of home-born litters plummeted.
At some point circa 1992 pet sterilization efforts reached the 70% target that prevents population growth.
By 1994 surveys in many parts of the U.S. began to confirm that about two-thirds of pet dogs and 80% of pet cats were sterilized. The researchers included Karen Johnson of the National Pet Alliance, Carter Luke of the Massachusetts SPCA, and Andrew Rowan, then heading the Tufts Center for Animals and Public Policy, now chief of staff for the Humane Society of the U.S.
The U.S. dog population since circa 1990 has been reproducing at approximately the rate of replacement and no longer seems to have any influence on cat numbers.
The U.S. pet cat population has reproduced at less than 70% of replacement, while absorbing up to 28 million formerly feral cats, primarily from litters collected by neuter/return practitioners as kittens.
Despite the enormous overall increase in the numbers of pet cats, the free-roaming pet cat population today appears to be down somewhat, perhaps mainly because of attrition among older cat-keepers, who are more inclined to think of cats as outdoor pets.
The decline in roadkills has apparently been so steep that since 1996 it has no longer been possible to presume, as the 1992 survey data indicated, that roadkills represent 10% of free-roaming cat mortality at population turnover rates of 100% among ferals and 33% among roaming pets.
If that was still true, there would now be only five million free-roaming cats left in the U.S., counting ferals, even though as many as 24 million pet cats are still allowed to roam.
What actually seems to be happening is that while the feral cat population is falling like a rock, predation has overtaken both roadkills and shelter killing as a cause of free-roaming cat mortality.
Estimating predation is awkward because of a paucity of data to work from, but ANIMAL PEOPLE found two ways to do it.
First, there were the reports of predation produced by the 1992 and 1996 cat rescuer surveys.
Second, ANIMAL PEOPLE in 1996 began tracking “predator panics” resulting from the discovery of cat remains, typically misattributed at first to human sadists.