TNR: Trap-Neuter-Return

Trap-neuter-return (TNR) is a type of program through which free-roaming cats are trapped, sterilized (males are castrated and females undergo ovo-hysterectomies), and returned to the outdoor locations where they were found. If those locations are deemed unsafe or otherwise inappropriate, the cats may be relocated (barn/farmyard homes are often considered ideal[1]). Kittens young enough to be socialized and friendly adult cats may be placed in foster care for eventual adoption into homes as companion animals rather than returned to the outdoors.[2] Cats found suffering with terminal, untreatable, and/or contagious illnesses or injuries are often euthanized.[3]

TNR is the most widely implemented method of managing cat populations. The main goal of a TNR program is the reduction of the feral cat population; other goals may include but are not limited to increased adoption rates, increased cat health, increased cat quality of life, and improved human-cat interactions.[4]

TNR is sometimes described as trap-neuter-release, changing the last word of the acronym.[5] This wording appears to have been the first version of the TNR acronym.[6] The word “return” emphasizes that most feral cats are returned to their original locations under this program. Other variations of the acronym include TNVR (trap-neuter-vaccinate-return),[7] TNRM (trap-neuter-release-maintain) where “maintain”, generally means caregivers feed and monitor the feral cats after they are returned to their territories,[8] and TTVAR (trap-test-vaccinate-alter-release).[9] TVHR (Trap Vasectomize-Hysterctomize-Release), a related acronym, refers to a different method of cat population management.[10]

History of TNR

U.K.

The earliest documented practice of trap-neuter-return was in the 1950s, led by animal activist Ruth Plant in the U.K.[11]:2 In the mid-1960s, former model Celia Hammond gained publicity for her TNR work[11]:2 “at a time when euthanasia of feral cats was considered the only option”.[12] Hammond “fought many battles with local authorities, hospitals, environmental health departments” but stated that she succeeded over the years in showing that control “could be achieved by neutering and not killing”.[12]

In 1975, Ruth Plant[11]:2 founded the Cat Action Trust to help feral cats using TNR.[13] From 1978 to 1979, biologist Roger Tabor mapped the distribution of 153 known feral cat colonies in central London, some being managed by the Cat Action Trust.[14]:91

In 1980, the Universities Federation for Animal Welfare (UFAW) organized the first international scientific symposium on “The Ecology and Control of Feral Cats” in London, where TNR experiences in the U.K. and Denmark were documented.[11]:2 The symposium was considered a “watershed occurrence” where attitudes toward feral cats began to shift toward humane treatment. In 1982, UFAW published a booklet promoting TNR: Feral Cats: Suggestions for Control.[11]:6

The Cat Action Trust reports that many thousands of feral cats have been neutered in subsequent years.[13] In 1986, Hammond founded the Celia Hammond Animal Trust to continue her work with feral cats, taming and rehoming hundreds of feral kittens each year;[15] and offering low cost neutering, which by 2014 was reported to have sterilized nearly 400,000 cats.[12]

In 2008, the Scottish Wildcat Association began utilising trap-neuter-return as a way to prevent hybridisation between feral cats and the locally endangered Scottish wildcat as part of the Wildcat Haven project.[16] In 2014 they announced over 250 square miles of remote wildcat habitat was now effectively feral cat free[17] through neutering the feral population, farm cats and pets with the support of the local community and local welfare groups.

Italy

Soon after visiting Venice, Italy, in 1965, Helena Sanders and Raymonde Hawkins initiated a program offering veterinary help, often for neutering, to assist cat caretakers there.[11]:48 After initial resistance from local animal protection societies, neutering schemes for city cats were accepted in many parts of Italy.[11]:48 The cats of Venice and Rome became famous as a result of the publicity given to their neutering programs.[18]:523 Since 1988, killing feral cats has been illegal in the Latium Region, which includes Rome. Since August 1991, feral cats have been protected throughout Italy when a no kill policy was introduced for both cats and dogs.[19] Feral cats have the right to live free and cannot be moved from their colony; cat caretakers can be formally registered; and TNR methods are outlined in the national law on the management of pets.[19]

Denmark

TNR was practiced in Denmark in the mid-1970s, as reported at the 1980 UFAW symposium in London.[11]:3 The Danish Cat Protection Society developed the practice of both tattooing and ear-tipping the ear of the neutered cats to identify them.[14]:187

South Africa

In the mid-1970s, Louise Holton worked with the Johannesburg SPCA on TNR programs in that city.[20] In 1991, Adele Joffe founded Friends of the Cat, a TNR organization in Johannesburg.[21] Holton continued to help feral cats in South Africa as part of her outreach efforts with Alley Cat Rescue, founded in 2001.[22]

France

In 1977, Michel Cambazard began to advocate for free-living cats at the Montmartre Cemetery in Paris, where the cats were routinely euthanized. In 1978, the city issued a Declaration of Rights of the Free-living Cat.[23] In that year, Cambazard founded École du Chat and TNR’d its first cat, continuing to help thousands of cats in the following years.[24]

United States

TNR goes back to the late 1960s in the U.S.[25] In approximately 1970, a group in Ocean County, New Jersey began its efforts.[11]:7 In 1984, AnnaBelle Washburn introduced TNR to Martha’s Vineyard, Massachusetts.[26]

In 1989, Nathan Winograd and others formed the Stanford Cat Network to assist about 1,500 cats at Stanford University in California, in probably the first formal TNR program at a U.S. campus.[27]:44[28] Within 15 years, the population at Stanford University had dropped to 85 cats.[27]:44 By 1990, other groups were also practicing TNR in Idaho, Nevada, Pennsylvania, and Colorado.[11]:7

In 1990,[29] Louise Holton and Becky Robinson discovered an alley with 56 cats and two smaller colonies in Washington, D.C., and neutered all the cats.[11]:8 Deluged by requests for help,[11]:8 and concerned for cats routinely being killed by animal control agencies and shelters, Holton and Robinson founded Alley Cat Allies.[30] They developed extensive educational materials, and organized national conferences beginning in 1994.[11]:9 They started a Feral Friends Network, which has a global reach.[31] The organization grew to 500,000 supporters and a staff of over 40 in 2014.[32] Holton left in 2001 to found Alley Cat Rescue.[29]

In the 1990s, a number of programs to help feral cats were initiated:

In 1992, San Diego’s Feral Cat Coalition developed the first high-volume feral cat sterilization program, where up to 150 cats were sterilized in a single day with the help of volunteer veterinarians and other volunteers.[27]:44[33][34] Other communities followed, including Operation Catnip in Raleigh, North Carolina in 1997,[35] and Operation Catnip in Alachua County, Florida in 1998.[36]

In 1993, led by Richard Avanzino,[37]:10 the San Francisco SPCA started a Feral Cat Assistance Program, offering free sterilization, advice and supplies to cat caretakers.[27]:44 The program was one of several reforms to create a no kill community.[38]:180

In 1994, PetSmart Charities began to provide grants toward sterilization programs for free-roaming cats and other animals; the organization’s website stated in 2014 that more than 2 million spay or neuter surgeries have been funded.[39]

In 1995, the Doris Day Animal League (DDAL) created the first annual “Spay Day USA”[40] on the last Tuesday of each February, which continues to help many feral cats and other animals as World Spay Day[41] after the DDAL’s merger with the Humane Society of the United States in 2006.[42]

In 1998, the Feral Cat Coalition of Oregon purchased a mobile clinic,[27]:44 which by August 2014 had neutered 70,000 cats.[43]

In 1999, Maddie’s Fund, the family foundation of Dave Duffield and his wife Cheryl,[37]:8 began to provide grants for large-scale neutering of feral cats. Between July 1999 and May 2002, 170,000 cats were neutered by over 1,000 veterinary members of the California Veterinary Medical Association in a $12 million project.[44]:42 Other programs were added, such as low cost sterilization,[37]:3 and research on shelter medicine;[37]:6 with the goal of helping to build a no kill nation.[37]:3

In Palm Beach County, Florida, a project called Countdown to Zero (C2Z), Project Catsnip was organized as a collaboration between government agencies, businesses, volunteers and residents working together to end euthanasia of feral cats in the community through spaying and neutering/ TNR. Together the community is using this approach to reach their goal of zero cats euthanized in the county.[45]

On October 16, 2001, Alley Cat Allies created the first annual National Feral Cat Day on the 10th anniversary of its incorporation[11]:8 “to raise awareness about feral cats, promote Trap-Neuter-Return, and recognize the millions of compassionate Americans who care for them”.[46] The event has attracted international participants.[46]

In 2001, under the leadership of Nathan Winograd, Tompkins County, New York became the first no kill community in the U.S.,[38]:180[47] “saving 100 percent of healthy and treatable animals, and 100 percent of feral cats”.[38]:180 In the No Kill Equation, a “roadmap to no kill”[48] developed by Winograd, TNR is one of the essential elements.[49]:4 Many communities followed this strategy in subsequent years.[50]

In 2008, a grant from Best Friends Animal Society supported a Feral Freedom program in Jacksonville, Florida, that saw the end of killing stray and feral cats in that city.[51][52] The program, conceived by Rick Ducharme of First Coast No More Homeless Pets, “has feral cats trapped by Jacksonville Animal Control bypass the shelter entirely in favor of being spayed or neutered and returned to the location where they were trapped.”[53] Similar programs were later implemented in Albuquerque, New Mexico,[53] DeKalb County, Georgia,[53] San Antonio, Texas,[54] Baltimore, Maryland,[54] Salt Lake City, Utah,[55] Philadelphia, Pennsylvania[56] and many other communities.[57]

TNR efforts in the U.S. have also encountered opposition. Traditional shelters disagreed with TNR, including the Humane Society of the United States,[38]:68 which later reversed its position.[58] The majority of traditional shelters continue to euthanize feral cats.[59] Wildlife groups such as the American Bird Conservancy blame cats for much of the reduction in U.S. bird populations, and in 1997 began its “Cats Indoors” campaign.[11]:18[60] TNR has gained increasing support over the years.[61]

Greece

In the 1980s, the Greek Animal Welfare Fund initiated the neutering of stray cats in Athens, supported by individuals in the U.K.[18]:522 The organization continues to be active, organizing a mass neutering drive for stray cats in Athens for October 2014.[62]

Virgin Gorda

In 1986, AnnaBelle Washburn worked with Tufts University’s School of Veterinary Medicine to sterilize feral cats on Virgin Gorda in the British Virgin Islands, “in one of the earliest partnerships between veterinary medicine and grass-roots organizations to improve the lot of feral cats”.[27]:44

Canada

Canada’s best known TNR effort was at the Cat Sanctuary of Parliament Hill in the nation’s capital, Ottawa, Ontario, where cats were employed for pest control until 1955.[63] Various people fed the remaining cats until 1970, when Irene Desormeaux began feeding them at their eventual colony location.[64] In the mid 1980s, Rene Chartrand built wooden housing for the cats and helped with their care, taking over when Desormeaux died in 1987.[64] In 1997 other volunteers joined in, and the structures were rebuilt.[64] In a brutal winter, “the cats survived marvellously cuddling up four or five at a time in the condos”.[65] However, neutering all the cats only occurred in the last ten to fifteen years of the sanctuary’s operation.[66] In 2013, the colony closed when the last four cats were adopted into homes.[66]

In 1989, Carol Reichert founded the Richmond Animal Protection Society (then Richmond Homeless Cats), to help feral cats in Richmond, British Columbia.[67][68] Soon 43 feeding stations were being tended in Richmond and south Vancouver.[67] In 1999, space was donated for a shelter,[67] which became Canada’s largest cat sanctuary, including space for cats with feline leukemia and feline AIDS.[69] The organization worked to spay and neuter many animals and worked to prevent pets from entering shelters.[67] Determined to “end needless euthanasia”, the organization made a successful bid for the city’s animal control contract, and in 2007, “implemented a no-kill policy for the animals regardless of age, medical needs or adoptability”.[67]

In 2000, Maria Soroski and Karen Duncan founded the Vancouver Orphan Kitten Rescue Association (VOKRA) in Vancouver, British Columbia.[70] They first planned to care for very young, mainly bottle-feeding kittens, who rarely survived if found without a mother cat.[71] They soon found that older kittens would do better in foster care, and then included mother cats, both tame and feral.[71] Care provided to feral cats includes caring for pregnant feral mothers through birthing and until their kittens are weaned.[71] By 2014, the organization had grown to over 350 foster homes helping 1,800 cats annually.[70] Soroski said they had “virtually eliminated feral cat colonies in Vancouver and Burnaby”, and had recently begun the same work in Surrey.[70]

In 2005, Pierre Filitreault began helping feral cats at a Halifax, Nova Scotia dockyard on a Canadian Armed Forces base.[72] Disappointed with what happened with two starving kittens he took to a shelter, he set up a TNR program, forming Pierre’s Alley Cat Society in 2007.[72] The Department of National Defense paid to have the cats neutered.[73]

Hong Kong

In 2000, the Hong Kong SPCA began a TNR program, called a Cat Colony Care Program (CCCP), in Hong Kong.[74] In 2014, the organization’s website reported a reduction in euthanasia from 40,000 cats in 1963 to 5,000 cats annually.[75]

Japan

In the 1990s a TNR program was started in Shiga Prefecture by Susan Roberts and David Wybenga of the Japan Cat Network (JCN). The JCN has also assisted with other TNR programs.[76]

Methodology

A feral cat recovering from her spay surgery.
Feral kitten, approximately nine months old, with the tip of his left ear removed to indicate he has been trapped and neutered.

The first trigger for a trap-neuter-return program is when free-roaming cats or kittens are seen in need and/or not having been neutered. A TNR program approaches the situation using the following recommended steps:

Preparation

Assess the cats and their environment. Do they appear to be stray or feral; are there kittens and/or nursing mothers; are there ill or injured cats? Plan ahead for the care to be provided after trapping.[77]:6

Communicate with neighbours and any caretakers. Build good community relations, working to address the concerns of others.[77]:5[78][79]:16

Establish a regular feeding schedule. This may involve providing feeding stations and winter shelters.[77]:7[79]:13

Secure a holding/recovery area where the cats can wait for surgery (if not immediate) and recover after surgery.[77]:11[79]:14

Find and coordinate with a veterinarian or clinic to perform the surgery and provide other medical treatment.[77]:7

Assemble trapping supplies, including humane traps, newspapers and other useful materials.[77]:11[79]:68

Withhold food (but not water) for about 24 hours before trapping, with the cooperation of caregivers and neighbours.[77]:14

Trapping

Bait and set the traps in a safe location, using as many traps as there are cats in the colony needing trapping.[79]:67

Wait patiently nearby but out of sight, for cats to enter the traps and the traps to close.[77]:15[79]:75

Quickly cover each occupied trap with a cover or sheet, which helps to calm the cat within.[77]:15[79]:76

Check whether each trapped cat is already owned or neutered (ear tip; identification tattoo or microchip; lost pet databases and ads), and take appropriate action.[80]

If trap occupants are wildlife, carefully release them.[79]:88
Safely transport the cats in their traps to the clinic or holding area.[77]:16
If a cat is too fearful or savvy of the regular box trap, try alternate traps and methods.[79]:91[81]

Neutering: Medical care and socialization

Provide extra care for cats not yet ready for surgery. Cats in poor condition may need to receive medical attention, gain weight and strength before surgery.[79]:109 Young kittens may be socialized in foster care, which prevents their becoming feral.[82] Nursing mother cats may be kept with their kittens (and even other orphaned kittens)[83] until the kittens are weaned.[84] “Kittens can be safely spayed or neutered at eight weeks, or as soon as they weigh two pounds (and are healthy).”[85]

When ready, a veterinarian performs spay or neuter surgery and provides other medical attention as needed.[86] Multiple surgeries may be done in high volume clinics.[87]

During the surgery of feral cats, ear-tipping (removing 3/8 inch or 1 cm from the tip of the left ear; proportionally smaller in a kitten) identifies that the cat has been neutered and treated, when later seen from a distance.[88]
Vaccinations are provided as arranged in advance. Common vaccines include rabies[89] and FVRCP, “the ‘distemper’ (panleukopenia) and respiratory virus vaccine”.[90]

Cats found suffering with terminal or untreatable illnesses or injuries are humanely euthanized.[91]
When the vet deems that the cats are ready to leave the clinic, transport them to the recovery area, and monitor them for at least 24 hours.[77]:17[92]
If needed, provide further nursing care (e.g. administering medications; providing recovery time from more complex surgery such as amputation).[79]:109[93][94]

Returning: The cats go home

If the original colony location is safe, transport the feral cats there and safely release them from their traps or carriers.[77]:18
If the location is not safe for feral cats, make other arrangements for farmyard homes.[79]:127[95]
Keep tame cats and kittens in foster care until they are adopted.[96] If there are insufficient resources to foster or shelter, the cats may be returned to outdoor colony locations in the same manner as feral cats.[52]
Keep detailed records of the cats assisted,[77]:5 and clean the traps and materials used.[92]

Caregivers monitor the outdoor colony locations, providing food, shelter, and medical care, and watching for any new abandoned cats requiring trapping.[97] Some communities with “Feral Freedom” programs return cats without ongoing monitoring by caregivers.[52]

Early in TNR work, some groups did routine testing for the feline leukemia virus (FeLV) and the feline immunodeficiency virus (FIV) prior to the neutering surgery. This practice is no longer recommended, due to problems such as unreliable results, the high cost of testing, and the low incidence of the viruses.[79]:120[98]

Rationale and effectiveness of TNR

Reduced population over time

Various long-term studies have shown that TNR is effective in stopping reproduction and reducing the population over time. An eleven-year study of a TNR program at the University of Central Florida achieved a population decrease of 66%, from 68 cats in 1996 (when the census was first completed after some trapping); to 23 cats in 2002.[44] No new kittens were born after 1995, and newly arrived stray or abandoned cats were neutered or adopted to homes.[44] It is important to realise however that this population reduction was primarily from adoption (47%) and euthenasia (11%), or simply the cats no longer living on site with their whereabouts unknown (15%),[44] and not from “releasing” the cats back to the situation they were found in.

A ten-year study of 103 colonies in Rome, Italy showed decreases within the colonies from 16% to 32%, with the highest number for colonies neutered 6 years before the study began.[19]:5 However, Natoli concluded that “This suggests that all these efforts without an effective education of people to control the reproduction of house cats (as a prevention for abandonment) are a waste of money, time and energy.”[144] Population decreases are expected when at least 71% to 94% of the cats are neutered.[145]:1779 TNR advocates also frequently cite a large-scale program on 103 cat colonies in Rome. Trapping and neutering decreased the populations of 55 cat colonies there, while the other 48 colonies either gained population or stayed the same.

In many cases, TNR has resulted in colonies closing when the last remaining cat died or was adopted. In the U.K., a TNR program at Stoke Mandeville Hospital ended with all the neutered outdoor cats having died, with none coming to take their place.[18]:522 TNR efforts in London’s Fitzroy Square in the late 1970s resulted in the colony ending by 1990 with all the cats having died.[18]:522 The cat sanctuary of Parliament Hill in Ottawa, Ontario, Canada, closed in January 2013, when the four remaining cats were adopted into homes.[146] One colony had already become extinct and another was approaching extinction within two years, in a study of 12 colonies in rural North Carolina.[147]:1363

TNR efforts may be hampered if colony locations are made public. An early 2003 study by Castillo of two colonies in popular public parks of Miami-Dade County, Florida revealed that highly visible, well-fed cat colonies attracted illegal abandonment of additional cats, including numerous kittens and females with litters.[148]:252[149]:1358 Despite dedicated efforts to trap and remove the newcomers as well as trap the existing cats, there was a slight increase in population from 81 to 88 cats over the year studied.[148]:251[149]:1358 Community strategies to reduce abandonment in general include providing low cost spaying and neutering for owned cats;[19]:5 improved pet retention programs, and expansion of no-kill animal sheltering.[149]:1358

Improved outcomes for cats: Life vs. death

The typical outcome for a feral cat taken to a traditional shelter which does not practice no kill sheltering is euthanasia.[59] This is often the outcome for timid or even friendly stray cats as well;[59][149]:1357 a study identified euthanasia in shelters as the leading cause of death of cats.[149]:1359

Since Santa Clara County, California began TNR in 2011, the county reported that “Thanks to this program, the shelter saw a 15% reduction in cat intake and an amazing 65% reduction in cat euthanasia.”[150] In a TNR program in Orange County, Florida, the numbers of cats euthanized decreased 18% in a six-year period after starting TNR.[151]:292

In September 2014, Johnson County, Indiana officials reported greater satisfaction with having saved the lives of hundreds of healthy cats in the program’s first year. “We’re not killing cats…. Not killing a healthy animal is always the right thing to do.”[152]

Improved outcomes for cats: Quality of life

TNR programs improve the welfare of the cats involved in many ways. They prevent the birth of kittens, who would be at risk of an early death in the wild.[149]:1359 Adult female cats are no longer burdened with cycles of repeatedly giving birth to and caring for kittens while fending for themselves.[153] Medical conditions such as infections, dental issues, and flea treatments are attended to when the cats are neutered.[79]:115 Spaying and neutering also increases their life expectancy;[154]:35 the cats are no longer subject to certain cancers,[153] and the chances of being hit by a car or injured in a fight drop a great deal.[155]

When programs provide for feral kittens to be socialized and adopted, and for friendly cats to be adopted, the welfare of those cats is improved.[79]:133 Cats returned to their original location are fed, monitored and receive ongoing care from caregivers; including being re-trapped if further medical needs arise.[97] Their health measurably improves, as they gain weight after being neutered,[156]:212 while having ample opportunity for exercise.[156]:210 One study suggests that although TNR “may not meet the gold standard of care desired for pet cats, it appears that sterilized feral cats can enjoy an extended period of good quality of life”.[149]:1359

Fewer complaints

Neutering cats makes them less likely to roam, spray urine and fight; resulting in fewer nuisance complaints.[157]:16 After starting a TNR program in December 1995, Orange County, Florida received fewer complaints about cats, even after broadening the definition of a nuisance complaint.[151]:296 A TNR program at Texas A&M University in 1998-2000 resulted in fewer complaints, showing that the remaining cats were less of a nuisance than they were previously.[157]:25

Cost savings

While neutering cats is costly, euthanizing them costs more.[158]:8 In Orange County, Florida, the average cost of impounding and euthanizing a cat was $139; while the average cost of surgery was $56.[151]:294 With 7,903 feral cats neutered over 6 years starting in December 1995, the county saved $656,000.[151]:295

In Port Orange, Florida a TNR program started in 2013 in the city’s business areas resulted in fewer stray cats and money saved.[159] In the first year, 214 cats were sterilized for $13,000, which was much less than over $50,000 spent in 2010, when most of the impounded cats were euthanized.[159] A further estimated $123,000 was saved for not having to impound the offspring of the now spayed cats.[159]

Improved morale and public support

TNR programs are able to garner stronger public support than programs that result in euthanasia.[27]:49 In 2007, Alley Cat Allies commissioned a survey by Harris Interactive, which found that Americans overwhelmingly (81%) considered it more humane to leave a stray cat outside to live out his life rather than having the cat caught and killed.[160]:1 The number was still high (72%) if the person knew that the cat would die when hit by a car in two years’ time[160]:2 (although the chances of being hit by a car are much less when a cat is neutered.)[155]

In London area hospitals in the U.K., patients resisted attempts to trap feral cats for euthanasia, but took a great interest in TNR programs; even offering to pay the veterinary fees out of their own pocket money.[18]:521 A TNR program in San Quentin State Prison in California, replacing the practice of euthanizing 100 to 250 cats each year, resulted in benefits to the inmates and staff, including “less violence and tension as well as being able to ‘model relatedness’ to other species and individuals”.[27]:51

In Orange County, Florida, a TNR program started in December 1995 improved the morale of everyone involved; citizens “who previously felt overwhelmed by the dilemma of feral cats they saw in their neighborhoods now feel empowered and able to make a difference in these cats’ lives”.[151]:297 At the same time, county animal services staff and citizens concerned about the cats were described as viewing each other “with a new perspective and understanding rather than as adversaries”.[151]:297
Alternatives ineffective and inhumane

Doing nothing can result in the numbers of feral cats increasing. A study of six managed colonies in rural North Carolina showed a 36% decline in population over two years, while three control colonies without TNR increased by 47% on average.[147]:1363 Further, animal welfare problems such as high rates of kitten mortality continue to occur.[147]:1362 One study suggests that “While still fairly common, this is not a responsible or constructive choice.”[27]:48

Removal is an alternative to TNR control their population.[145]:1780 Eradication programs “often require years to accomplish and hundreds of hours of work and are only successful in closed populations where no new cats can arrive”.[27]:48 Further, methods used often involve poisoning, shooting, hunting, and other methods considered animal cruelty in many North American jurisdictions.[133][140] Trapping and removal of cats by euthanasia has been used in many communities, but almost never results in a permanent decrease in the cat population.[27]:48 “It is extremely difficult to remove every cat in a particular location, and most locations are not sufficiently isolated to prevent migration of new cats into the ecological vacuum created by cat removal. If there is sufficient food and shelter, new cats will move in from nearby areas, and survivors of the removal program will continue to reproduce until the maximum carrying capacity is reached again.”[27]:48 Many local and state governments have turned to TNR as a more effective and humane approach to control feral cat populations.[61]:11[150][159]