25 years of neuter/return has effect comparable to reducing average litter size from four kittens to one
MOUNT RANIER, Maryland––The largest return of data yet from a national survey of cat rescue and sterilization programs shows a cumulative reduction of 72% in kitten births at monitored colonies since the introduction of neuter/return feral cat population control.
(See also Feral cats: the true tale behind the tails.)
Half of all TNR done in past five years
The data, collected by Alley Cat Rescue, also suggests that more than half the cats who have ever been sterilized by neuter/return programs were sterilized in the 2012-2017 time frame: more in just the past five years than in the preceding 20.
To more accurately assess what the numbers mean, ANIMALS 24-7 has compared the 2017 Alley Cat Rescue findings not only to the findings of a similar survey done by Alley Cat Rescue in 2012, but also to the findings from two national surveys of cat rescuers done by ANIMALS 24-7 editor Merritt Clifton.
Walt Disney did it but didn’t admit it
The first of the Clifton surveys was done in 1992, soon after Alley Cat Rescue founder Louise Holton, Alley Cat Allies founder Becky Robinson, and others introduced the neuter/return technique to the U.S. on a large scale––although, as author Gavin Ehringer has recently detailed in Leaving The Wild (2017), entertainment entrepreneur Walt Disney covertly established a mega-sized neuter/return feral cat colony at the original Disneyland in Anaheim, California as early as 1955.
The second Clifton survey, done in 1996, collected data from 44 of the 190 respondents to the first survey.
Together, the data from the four surveys done over 25 years document enormous reductions in the numbers of cats living outdoors, outside of homes, and also document enormous changes in related factors such as reproductive rates and longevity.
From plateau to quantum leap
After having reached a plateau between 1996 and 2012 in what could be done with limited funds and volunteer labor, cat rescue and sterilization programs have achieved a recent quantum leap in growth and public acceptance, the Alley Cat Rescue findings indicate.
Since 2012, Alley Cat Rescue found, neuter/return programs around the U.S. have become more professional, much more likely to work in partnership or under the auspices of established humane societies or animal control agencies, with more resources of every kind, more volunteers, more employees, and much more community recognition of the utility of the neuter/return technique, commonly abbreviated as TNR (for trap/neuter/return) and sometimes as TNVR (for trap/neuter/vaccinate/return).
All of these methods, and the method often called return-to-field by animal control agencies, refer to essentially the same technique, regardless of the differences in terminology: sterilizing cats found at large, vaccinating them against rabies and possibly other diseases, and then returning them to wherever they were caught, to live out their normal lives.
96% rabies vaccination rate
All four surveys, 1992, 1996, 2012, and 2017, have confirmed a rabies vaccination rate in neuter/return programs of about 96% of the cats handled (nearly twice the U.S. dog vaccination rate of 55%), with most or all of the cats left unvaccinated having been under six months of age, meaning too young to vaccinate successfully, because those cats’ immune systems have not yet matured.
The 2017 Alley Cat Rescue survey verified that 97% of the cats in neuter/return programs have been ear-tipped for identification. About two-thirds of the cats also receive vaccinations against distemper, deworming, and flea prevention treatment.
About half are tested for feline leukemia and/or feline immunodeficiency virus. Of the remainder, about half are spot-checked for FeLV and FIV if there are indications that either disease may be present in or near a neuter/return colony. Altogether, under 25% of the cats are vaccinated against FeLV and FIV, neither of which has been discovered in more than about 2% of the cats tested.
Limited resources held back progress
The plateau in neuter/return accomplishment, as of 2012, was most visible in the kitten birth rate among monitored colonies. While a 48% decline in kitten births was visible in monitored neuter/return colonies by 1996, the kitten birth rate edged down only 4% more in the next 16 years.
The 2012 Alley Cat Recue data strongly suggested that neuter/return projects would need more funding, more skilled cat-trappers, and more ability to work in hard-to-access habitat to further reduce the U.S. feral cat population.
Eight million feral cats
As of 2012 the U.S. feral cat population, meaning cats surviving on their own, without more than incidental human intervention, had for about 10 years hovered at around six million in the dead of winter, 12 million at the peak of “kitten season” in mid-summer, as indicated by a variety of roadkill counts, habitat surveys, and animal shelter intake data.
This was about 25% of the 1990 estimated peak feral cat population of as many as 40 million, but almost all of the decline was achieved before 2003, as underfunded volunteers sterilized the most accessible cats and then continued to sterilize enough to hold their gains, but not enough to make further steep reductions.
Smaller & fewer cat colonies
The evolution of feral cat colony sizes tells the story.
As of 1992, only 6% of known cat colonies had more than 20 cats, but these tended to be mega-colonies, many of 50 cats or more. Colonies of more than 100 cats were not unusual.
Altogether, 63% of the outdoor cat population surveyed in 1992 were in the biggest 16% of cat colonies.
These tended to be the colonies where neuter/return had the most immediate and most dramatic effect.
Mega-colonies near vanishing point
Currently, according to the 2017 Alley Cat Rescue data, only 9% of the outdoor cat population are in colonies of 30-plus, and only 30% (including the 9%) are in colonies of 20-plus. Larger mega-colonies appear to have dwindled toward the vanishing point.
The percentage of cats in smaller colonies of 10 cats or fewer has also decreased, from 31% in 1992, and about the same in 2012, to 22% in 2017, even though the smaller colonies are about half the total number of colonies surveyed.
This appears to reflect the success of neuter/return practitioners in “zeroing out” many smaller colonies, and diminishing the rest.
The percentage of cats in mid-sized colonies of eleven to twenty cats, 36% of the known colonies, has increased from 6% to 48%.
While in theory some smaller colonies could have grown larger, the increase in the number of cats in mid-sized colonies actually appears to reflect the success of neuter/return in preventing mega-colonies from forming. Colonies which formerly grew to mega-size are now being found and sterilized long before approaching whatever may be the upper end of the carrying capacity of their habitats.
Some things have not changed nearly as much.
Comparing the data from the four surveys done over 25 years confirms that cats in neuter/return programs live significantly longer than cats at large did, on average, before neuter/return caught on.
But this must be assessed with the understanding that outdoor cat mortality is still very high, and that the change, visible by 1996, is entirely in the longevity of those cats who survive their first year at large.
Half die or disappear within a year
The 2017 Alley Cat Rescue numbers indicate that about half the cats in neuter/return programs die or disappear within a year, about the same first-year mortality rate as was observed in 1992.
Of the remainder, 76% survive from two to six years, about half again more than did before the advent of neuter/return; 17% survive from six to 10 years; and 3.4% live for 10 years or longer, about triple the rate of pre-TNR survival to relative old age.
The 2017 data compares closely to the survival rates for sterilized outdoor cats found in 1996 and 2012.
Causes of death & disappearance
What do outdoor cats die from?
Before 1991-1992, nearly half of known outdoor cat mortality, as estimated from 2,638 documented cat deaths, was due to animal control and “nuisance wildlife” trapping activity.
The advent of neuter/return in 1991-1992 cut these causes of death to about 25% of known mortality among cats in monitored colonies.
Animal control and “nuisance wildlife” trapping activity still appears to account for about 25% of known mortality among cats in monitored colonies.
“Natural causes,” chiefly disease, accounted for 31% of deaths in monitored colonies in 1992, 30% in 2017.
“Suspicious” deaths & roadkill
What the Alley Cat Rescue surveys term “suspicious” deaths, including predation by wildlife, accounted for 15% of mortality in 1992, but 23% in 2012 and 22% in 2017. This number can be expected to remain steady or trend further upward, because as the numbers of cats who hunt for a living goes down, the numbers of other predators hunting mice and rats tends to increase. Many of those predators, including coyotes, foxes, fishers, and bobcats, also prey on outdoor cats, as opportunity permits.
Roadkill mortality has declined from 29% of known outdoor cat deaths in 1992 to 22% and 23% in the Alley Cat Rescue surveys of 2012 and 2017. This probably reflects mainly that the outdoor cat population of recent years has included far fewer not-yet-car-savvy juveniles. As the numbers of outdoor cat births decline, roadkill mortality can be expected to continue to decline.
Progress to 2012
As of 2012, 120 responding programs responding to the Alley Cat Rescue survey had cumulatively sterilized and returned to their habitat about 618,000 feral cats, at an average pace of approximately 45,000 cats per year.
The respondents appeared to be about 17% of the U.S. feral cat neuter/return programs believed to have been active in 2012.
If the non-responding programs had worked at about the same pace, neuter/return programs might cumulatively have sterilized 3.6 million cats in 20 years.
Taking mortality into account, and estimating that the U.S. feral cat population as of 2012 was about eight million on year-round average, between 20% and 25% of the feral cats at large in 2012 might have been sterilized.
From then to now
As of 2017, Alley Cat Rescue discovered, 204 responding programs had cumulatively sterilized and returned to their habitat at least 1.3 million cats, at an average pace of more than 100,000 cats per year.
Among them, the respondents had at least 45,100 cats in monitored colonies, and might have boosted the feral cat sterilization rate to circa 50%. About 4,000 cats from monitored colonies had been rehomed, two-thirds of them kittens.
70% or fail
A 70% rate of prevention of births, combining sterilization with mortality, is necessary to stabilize a population of outdoor cats, or practically anything else from viruses to whales and elephants.
As outdoor cat mortality remains high, the 2017 Alley Cat Rescue findings suggest that the U.S. feral cat population should again be rapidly dropping, as it did from 1992 to 1996 before reaching the long plateau.
Yet there are several countervailing factors which may together be making cats who live mostly outdoors much more visible now than in 1992, 1996, and 2012.
Why more cats may be seen
One of those factors is simply that cats in fed neuter/return colonies tend to change their behavior. Instead of hunting rodents for a living, mostly by night when rodents are most active, hiding and resting during the day, fed cats become tamer, more inclined to show themselves by day, and to hunt birds, which requires a high investment of energy for relatively low return in food value.
Another factor of significance is that because far more agencies are involved in neuter/return programs now than in 2012 and before, those programs tend to have a much higher community profile.
Also, cats who live longer have more opportunity to be seen and recognized.
Alley Cat Rescue in a prepared release announcing their 2017 survey findings spotlighted that “Seventy-five percent of the groups surveyed said they find working with their local county-run shelters ‘easy’ or ‘intermediate.’
“In comparing these results to those from 2012,” Alley Cat Rescue said, “the relationships between animal control agencies and feral cat rescues have shown a 16% improvement. Similar progress has been made in regards to the relationships between cat organizations and local governments, with a 22% decrease in feral cat rescues finding it ‘difficult’ to work with local policymakers.”
Professionalism, age, & experience
Much of this is likely due to increased professionalism on the part of neuter/return program operators.
More than 70% of the 204 cat rescue and sterilization organizations responding to the 2017 Alley Cat Rescue questionnaire had fewer than three paid employees, but in 1992 there were no paid employees among 190 cat rescue and sterilization programs, other than a handful of veterinarians and veterinary technicians.
Another big part of the improved relations between neuter/return programs and public agencies appears to be just that the neuter/return programs have been around longer, having more time to become recognized community institutions.
About 85% of the programs responding to the 2017 Alley Cat Rescue survey have operated for at least five years; 37% for at least fifteen years; and 15% are old enough to have been among the respondents to the 1992 survey, though no attempt was made to match respondent identities.