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.
Roaming continues
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.
Fecundity drops
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.
Predation triples
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. From 1996 through 2000,
the numbers of such panics around the U.S. ranged from a high of 19
in 1997 to a low of seven in 1999, averaging 11 with a median of 10.
Then the number of “predator panics” tripled in 2001,
remaining at the same level in 2002 and 2003.
The combination of data suggests that wildlife predation on
outdoor cats was constant but relatively infrequent compared to
roadkills until the numbers of cats fell to the point that enough
prey was left unclaimed to sustain larger predators capable of
killing a cat as well as mice, rats, and rabbits.
The balance apparently tipped in 2001.
Perhaps not coincidentally, 2001 also appears to have been
the first year in decades that the U.S. whitetailed deer population
and roadkills of deer began to dip significantly, after 40 years of
rapid increase. Instead of scavenging as many deer as previously,
suburban coyotes in particular were forced to more vigorously hunt
small prey, including cats.
The U.S. feral cat population may have been reduced to as few
as five million. Now free-roaming pet cats are at proportionally
greater risk from wild predators–and are more likely to be missed by
grieving keepers.
Those who have lost pet cats to wild predators often respond
by clamoring for the deaths of the predators, as in Rutland,
Vermont, where state wildlife officials in October 2003 trapped and
killed a pair of rare fisher cats (cat-like relatives of ermine) for
having killed house cats in back yards.
The recent rates of progress against pet overpopulation in
the U.S. and of reclamation of urban and suburban habitat by native
wildlife have been so rapid that it is possible to anticipate a
future, not far away, when animal advocates will have to turn much
of the effort now put into sterilizing feral cats toward teaching the
public how to live peaceably with native wildlife.
The importance of sterilizing pet cats and not letting them
roam outdoors unsupervised will almost certainly remain central to
the humane education curriculum.
