Trap-neuter-return (TNR) is a program through which free-roaming community cats (not belonging to particular humans) are humanely trapped; sterilized and medically treated; and returned to the outdoor locations where they were found. If those locations are deemed unsafe or otherwise inappropriate, feral cats (unsocialized to humans) are relocated to farmyard homes. Kittens still young enough to be socialized, and friendly adult cats, are typically placed in foster care for eventual adoption into homes as companion animals, rather than returned to the outdoors. Cats found suffering with terminal or untreatable illnesses or injuries are humanely euthanized.
TNR is endorsed by the American Society for the Prevention of Cruelty to Animals (ASPCA) as "the most humane, effective and financially sustainable strategy for controlling free-roaming cat populations"  and "the only proven humane and effective method to manage feral cat colonies." The Humane Society of the United States has also endorsed "community-based Trap-Neuter-Return (TNR) programs with on-going responsible management as the most viable, long-term approach available at this time to reduce feral cat populations." The American Humane Association is another supporter of TNR. In Canada, the Canadian Federation of Humane Societies supports TNR, stating that the care of feral cats "is society's responsibility" as their wild nature is the result of human neglect. The U.K.'s Royal Society for the Prevention of Cruelty to Animals (RSPCA) supports "trapping and neutering of feral cats where local charities have the capacity to do so." Worldwide supporters include the World Animal Foundation, based in Oneida, Kentucky, and the International Companion Animal Management Coalition.
North American wildlife organizations including the American Bird Conservancy, The Wildlife Society and others, oppose TNR. They dispute its effectiveness at reducing feral cat populations, and claim that free-roaming cats are responsible for much of the decline in bird populations over the last number of years, killing 1.4 to 3.7 billion birds annually in the U.S. Rather than TNR, they recommend that free-roaming cats be trapped and taken to local animal shelters or humanely killed.
TNR advocates counter that cat predation is inflated, based on unscientific studies that extrapolate from tiny samples and project them onto whole nations. They point out that removing feral cats en masse can harm the environment and even birds; killing healthy cats (the usual result if feral cats are taken to animal shelters) is inhumane, and even more expensive for public officials than TNR; and research and experience of TNR shows that community cat populations indeed decline. In the U.K., The Royal Society for the Protection of Birds states that there is no evidence that cat predation "is having any impact on bird populations UK-wide".
TNR is sometimes described as trap-neuter-release, changing the last word of the acronym. This wording appears to have been the first version of the TNR acronym. The word "return" emphasizes that most feral cats are returned to their original locations under this program, and is the word most in current use. Some programs also go by other acronyms: TNVR (trap-neuter-vaccinate-return) adds emphasis to the process of vaccinating the cats for diseases like rabies before their return to the outdoors. TNRM (trap-neuter-release-maintain) adds the word "maintain," emphasizing the final part of the program, where caregivers feed and monitor the feral cats after they are returned to their territories. TTVAR (trap-test-vaccinate-alter-release) adds details about testing undertaken for serious illnesses, but this acronym is not in wide usage.
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:
- 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.
- Communicate with neighbours and any caretakers. Build good community relations, working to address the concerns of others.
- Establish a regular feeding schedule. This may involve providing feeding stations and winter shelters.
- Secure a holding/recovery area where the cats can wait for surgery (if not immediate) and recover after surgery.
- Find and coordinate with a veterinarian or clinic to perform the surgery and provide other medical treatment.
- Assemble trapping supplies, including humane traps, newspapers and other useful materials.
- Withhold food (but not water) for about 24 hours before trapping, with the cooperation of caregivers and neighbours.
- Bait and set the traps in a safe location, using as many traps as there are cats in the colony needing trapping.
- Wait patiently nearby but out of sight, for cats to enter the traps and the traps to close.
- Quickly cover each occupied trap with a cover or sheet, which helps to calm the cat within.
- 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.
- If trap occupants are wildlife, carefully release them.
- Safely transport the cats in their traps to the clinic or holding area.
- If a cat is too fearful or savvy of the regular box trap, try alternate traps and methods.
- 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. Young kittens may be socialized in foster care, which prevents their becoming feral. Nursing mother cats may be kept with their kittens (and even other orphaned kittens) until the kittens are weaned. "Kittens can be safely spayed or neutered at eight weeks, or as soon as they weigh two pounds (and are healthy)."
- When ready, a veterinarian performs spay or neuter surgery and provides other medical attention as needed. Multiple surgeries may be done in high volume clinics.
- 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.
- Vaccinations are provided as arranged in advance. Common vaccines include rabies and FVRCP, "the 'distemper' (panleukopenia) and respiratory virus vaccine".
- Cats found suffering with terminal or untreatable illnesses or injuries are humanely euthanized.
- 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.
- If needed, provide further nursing care (e.g. administering medications; providing recovery time from more complex surgery such as amputation).
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.
- If the location is not safe for feral cats, make other arrangements for farmyard homes.
- Keep tame cats and kittens in foster care until they are adopted. 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.
- Keep detailed records of the cats assisted, and clean the traps and materials used.
- Caregivers monitor the outdoor colony locations, providing food, shelter, and medical care, and watching for any new abandoned cats requiring trapping. Some communities with "Feral Freedom" programs return cats without ongoing monitoring by caregivers.
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.
In the United States feral cats as exotic feral carnivores have no legal protection, as the native wildlife does. Any exotic animal, if they are not owned by someone, technically are a potential target that can be legally trapped and euthanized under the State nuisance laws. Many states do not even have an adequate definition of what a "feral cat" is, such as California and its State Codes. Furthermore, when Cities or Counties support TNR policies, they have been stopped with court actions when an environmental review was not completed to analyze the impact of releasing feral exotic carnivores into the environment. The case Urban Wiildlands Group v. The City of Los Angeles  stopped that city's TNR program because of a lack of an environmental review. The conflict between Listed Endangered Species and feral cats is a perennial legal problem, and Broward County in Florida has decided to solve that conflict by converting from a TNR program, to the new TSAFE  (Trap-Sterilize-Adopt-Foster-Euthanize). TSAFE program is designed to end the release of feral exotic carnivores into the environment.
Supporters of TNR embrace this practice as part of a "no-kill" philosophy. Euthanasia on a massive scale is not fiscally practical. TNR advocates agree that the traditional methods of trapping-and-removing will not work because of a "vacuum effect": As some cats are taken out of their territory, others will move in to replace them, which renders the initial removal ineffective. However, there is little to no scientific evidence to support this claim. If other feral cats are available to do so, the primary factor of whether they will or not is the availability of food: If enough food is present, then any nearby cats may move in.  This, however ignores one simple fact. The food supply for most "community cats" is food provided to them by people. If people are prevented from feeding free roaming cats, there will be nothing to attract other cats to replace those removed.
Studies have been conducted to gauge the effectiveness of TNR. Several of them suggest that the procedure works. A PhD study in North Carolina found that TNR consistently reduced the populations of feral cat colonies by a mean of 36% over two years and with the extinction of one third of the colonies within the same period, while the non-TNR'd colonies increased by a mean of 47%. One peer-reviewed study showed a reduction in numbers of cats with TNR by 66% over an 11 year period.
However, a study by Castillo (2003) found that TNR was ineffective due to feeding locations attracting even more feral cats while also providing a convenient place to illegally dump unwanted cats, although advocates argue that dumping is a separate issue and does not invalidate TNR. A review article by Longcore et al. (2009) argues that TNR advocates are too concerned about cat welfare and not about the effect on indigenous wildlife. The authors argue that populations are not stable and movement of cats is significant between urban areas and nearby woodland. They also state that cats can reach high densities when there is a reliable food source without proper sterilization and management. California State University researchers published mathematical models of feral cats populations suggesting that 71–94% of a population needs to be sterilized for the population to decline, based on case studies of San Diego and Alachua Counties.
Effect on wildlife
The trap-neuter-return approach is controversial. Many wildlife and bird advocacy organizations argue that TNR does nothing to address the possibility that predation by feral cats could threaten endangered species. TNR groups state that the effect of habitat destruction is caused by irresponsible human development and not by feral cat colonies.
Longcore et al. found that feral cats harm wildlife on continents as well as islands, and that there have been recorded instances of bird extinction from feral cats on islands. Their paper also argues that fragmented ecosystems near urban areas are similar to islands and more susceptible to feral cat damage, and that feral cats in urban areas also pose significant risk to migratory birds. The authors argue that feral cats are exotic and do not fill an existing niche and that even well-fed cats significantly impact on wildlife. The article details population and comparative studies of the adverse effects of feral and free roaming cats on birds and other wildlife. However, longer and more detailed studies need to be done on this subject. The authors also argue that feral cats act as vectors for diseases that can impact domestic cats, wildlife and humans, examples include feline leukemia virus, feline immunodeficiency virus, fleas and ear mites (which are also carried by canines and wildlife), hookworms, roundworms, Bartonella, Rickettsia, Coxiella and Toxoplasma gondii, and that fecal matter has also been shown to degrade water quality.
The International Union for Conservation of Nature states that feral cats have been responsible for the extinction of at least 33 bird species world-wide. However the Royal Society for the Protection of Birds has argued that cats do not pose a significant threat to wild bird populations in the United Kingdom.
- "'Community cat' is an umbrella definition that includes any un-owned cat. These cats may be 'feral' (un-socialized) or friendly, may have been born into the wild or may be lost or abandoned pet cats. Some community cats are routinely fed by one or more community members, while others survive without human intervention. Whatever a cat's individual circumstances, the term 'community cat' reflects the reality that for these cats, 'home' is within the community rather than in an individual household." Kate Hurley and Julie Levy, Maddie's Institute: "Feline Shelter Intake Reduction Program FAQs", January 2013. This reference also discusses TNR of community cats.
- for example, Kitsap Humane Society, Silverdale, WA, "BARN CAT PROGRAM", accessed June 19, 2014.
- "Whenever possible, adoptable cats and kittens should be removed from a feral colony for placement in good homes." "Neighborhood Cats TNR Handbook, 2nd edition: The Guide to Trap-Neuter-Return for the Feral Cat Caretaker", Bryan Kortis, Neighborhood Cats, 2013, p. 133.
- "At Neighbourhood Cats, we euthanize cats only if they are actively ill, suffering and terminal." Ibid., p. 124.
- "Position Statement on Feral Cat Management", American Society for the Prevention of Cruelty to Animals, accessed June 20, 2014,
- "Feral Cats FAQ", ASPCA, second paragraph, accessed June 20, 2014. Resources provided here on TNR and feral cats.
- "HSUS Position Statement: Trap-Neuter-Return (TNR) Humane Society of United States, March 20, 2006. Many resources are offered on TNR:"What You Can Do To Help Feral Cats", Humane Society of the United States, July 3, 2013, accessed June 20, 2014.
- "American Humane Association: Animal Welfare Policy and Position Statements", p. 9, accessed July 17, 2014.
- "Feral Cats", The Canadian Federation of Humane Societies, accessed June 23, 2014.
- "Stray and Feral Cats", Royal Society for the Prevention of Cruelty to Animals, accessed June 23, 2014.
- "Trap-Neuter-Return: Saving Feral Cats", World Animal Foundation, accessed June 23, 2014
- "Humane Cat Population Management Guidance", International Companion Animal Management Coalition, accessed July 19, 2014.
- The American Bird Conservancy has an extensive "Cats indoors" campaign against TNR and free-roaming cats: "Cats Indoors: Better for Cats. Better for Birds. Better for People."
- "Problems with Trap-Neuter-Release", The Wildlife Society, updated Feb. 2011. See also "Final Position Statement: Feral and Free-Ranging Domestic Cats", The Wildlife Society, "Approved by Council August 2011. Expires August 2016". The Wildlife Society is based in Bethesda, Maryland.
- Trap-Neuter-Return: The wrong solution to a tragic problem", American Bird Conservancy, accessed June 23, 2014.
- "Free-Roaming Cats: A Conservation Crisis", American Bird Conservancy, accessed June 24, 2014. See also "That Cuddly Kitty Is Deadlier Than You Think", Natalie Angier, New York Times, January 29, 2013, and "The impact of free-ranging domestic cats on wildlife of the United States", Scott R. Loss et al, Nature Communications, January 29, 2013, the most recent study from which the estimates of bird kills by cats arose.
- "What to do about unwanted cats in your yard", American Bird Conservancy, accessed June 23, 2014.
- "'I detest the killing of cats and dogs or anything else,' says George Fenwick, president of the American Bird Conservancy. 'But this is out of control, and there may be no other answer.'" "Free-roaming cats stir emotional debate on bird safety", Chuck Raasch, USA Today, Oct. 3, 2012. The Wildlife Society is more open about recommending killing of cats in their position statement: "Support and encourage the humane elimination of feral cat populations, including feral cat colonies, through adoption into indoor-only homes of eligible cats and humane euthanasia of unadoptable cats." "Final Position Statement: Feral and Free-Ranging Domestic Cats", The Wildlife Society, "Approved by Council August 2011. Expires August 2016".
- "Setting the Record Straight", Alley Cat Allies, links to fact sheets and articles critiquing several studies. One is Gregory J. Matthews' critique of the Scott R. Loss et al January 2013 article in Nature Communications from which the 1.4 million to 3.7 billion bird deaths estimate now in use arose: "A review of the statistical methods employed in the article 'The impact of free-ranging domestic cats on wildlife of the United States'", Feb. 4, 2013. Some of his comments were that the article was filled with "numerous major ﬂaws in the statistical arguments made" that made it "unacceptable for publication"; it was unclear how predation rates were obtained, and then "applying these estimates to all cats across the country is highly questionable"; and extrapolation was wrong: "Based on a small sample of cats over three summer months in one speciﬁc geographic area, the authors see ﬁt to extrapolate this predation rate to all cats at all times of the year in all geographic regions in the United States."
- "Biology and Behavior of the Cat", Alley Cat Allies, has many links, includes "Understanding Ecosystems: Why Removing Cats is Worse for Everyone" which covers a variety of topics. See also this link for one example of possible benefits of feral cats to endangered wildlife: "Feral cats help some endangered mammals survive, report says", Gabriel Popkin, The Sydney Morning Herald, August 29, 2013.
- "Feral or very fearful community cats have historically been euthanized either immediately or at the end of a holding period at most shelters." Kate Hurley and Julie Levy, Maddie's Institute: "Feline Shelter Intake Reduction Program FAQs", January 2013, subheading "What happens to community cats in animal shelters?"
- "TNR saves taxpayers money by reducing wild, free-roaming cat populations which in most cases end up in municipal shelters and have to be euthanized", "Community/Feral Cats: Trap/Neuter/Return: What it is and why it works", Best Friends Utah, accessed June 24, 2014; see also "Free to Roam: A Small City's New Policy that Saves Feline Lives and Tax Payer Money", Maddie's Institute, May 2013. For savings involved in implementing TNR combined with other measures of no kill animal sheltering, see "Dollars and Sense: The Economic Benefits of No Kill Animal Control", The No Kill Advocacy Center.
- "Evaluation of the effect of a long-term trap-neuter-return and adoption program on a free-roaming cat population", Julie K. Levy et al (JAVMA, Vol 222, No. 1, January 1, 2003) - Eleven year study of a TNR program at an urban university campus in Florida, where among other benefits, populations of free-roaming cats declined. For a detailed response to a critique of TNR, see Peter J. Wolf, Vox Felina, 2010, "Reassessment: A Closer Look at 'Critical Assessment of Claims Regarding Managment of Feral Cats by Trap-Neuter-Return'".
- "Trap-Neuter-Return Effectively Stabilizes and Reduces Feral Cat Populations", Alley Cat Allies. Case studies of TNR programs from Chigaco to San Francisco to Rome, Italy. Some colonies reduced to zero residents when the last remaining feral cat died (Washington, D.C. at age 17, Newburyport, MA at age 16).
- "This may be surprising, but many millions of birds die naturally every year, mainly through starvation, disease, or other forms of predation. There is evidence that cats tend to take weak or sickly birds….Those bird species that have undergone the most serious population declines in the UK (such as skylarks, tree sparrows and corn buntings) rarely encounter cats, so cats cannot be causing their declines. Research shows that these declines are usually caused by habitat change or loss, particularly on farmland." "Are cats causing bird declines?" The Royal Society for the Protection of Birds, accessed June 23, 2014.
- for example, Joe Vaccarelli, "Denver Animal Shelter partners up to help reduce feral cat population", The Denver Post, June 12, 2014
- Ellen Perry Berkeley, "TNR: Past, Present and Future: A History of the Trap-Neuter-Return Movement" (Washington: Alley Cat Allies, 2004), p. 1
- for example, Humane Society of Tampa Bay, "TRAP / NEUTER / VACCINATE / RETURN (TNVR): What is TNVR?", accessed June 15, 2014. Note that at this link, the organization also used the term TNR to refer to the program: "In December 2011, Hillsborough County Commissioners passed a resolution recognizing Trap-Neuter-Return to better control community cat populations." and adding a link to a Youtube video, "Why TNR is better than trap and kill."
- Society for the Prevention of Cruelty to Animals, Montreal, Quebec, "Do you know about our TNRM program?", July 5, 2013, accessed June 15, 2014
- for example, National Pet Alliance "NPA's TTVAR Program: Trap, Test, Vaccinate, Alter and Release", accessed June 15, 2014.
- "How to Help Feral Cats: A step-by-step guide to Trap-Neuter-Return", Alley Cat Allies, 2009, updated 2002, accessed June 19, 2014. Hereinafter "ACA TNR Guide."
- ACA TNR Guide, pp. 6-7.
- ACA TNR Guide p. 5; "Community Relations Resource Center", Alley Cat Allies, accessed July 10, 2014; and Bryan Kortis et al, "Neighbourhood Cats TNR Handbook: The Guide to Trap-Neuter-Return for the Feral Cat Caretaker", Neighbourhood Cats, 2nd. edition, 2013, pp. 13 and 16-27 (http://www.neighborhoodcats.org/uploads/File/Resources/NC%20TNR%20Handbook_PRINT_v5-4.pdf), hereinafter "NC TNR Guide."
- ACA TNR Guide p. 7, NC TNR Guide p. 13.
- ACA TNR Guide p. 11, NC TNR Guide p. 14.
- ACA TNR Guide pp. 7-10.
- ACA TNR Guide pp. 11-12, NC TNR Guide pp. 68-70.
- ACA TNR Guide p. 14.
- NC TNR Guide p. 67 discusses Mass Trapping.
- NC TNR Guide p. 75, ACA TNR Guide p. 15.
- ACA TNR Guide p. 15, NC TNR Guide p. 76.
- "How to Find Homes for Stray Cats: 1 Try to find the cat's home", Alley Cat Allies, accessed July 11, 2014. In Canada, consider "Helping Lost Pets: A Free National Pet Registry", database based in Ontario, and "Petsearchers Canada", service based in British Columbia.
- NC TNR Guide pp. 88-90 has tips including feeding suggestions that deter wildlife.
- ACA TNR Guide p. 16
- NC TNR Guide pp. 91-103; "Tips for Successful Trapping of Trap-Shy Cats", Alley Cat Allies, accessed July 10, 2014.
- NC TNR Guide p. 109.
- "Socializing Feral Kittens", Alley Cat Allies, accessed July 11, 2014; and "Taming Ferals1", Urban Cat League, New York City, accessed July 11, 2014.
- "Kittens get second chance with surrogate mamas", Vincent T. Davis, MySA, April 23, 2013.
- "Fosters are desperately needed…", MCA Society, Conroe, Texas, accessed July 10, 2014; nursing mother cats are taken out of the shelter into foster care right away to prevent upper respiratory infection (URI).
- "Protocols: Early-Age Spay and Neuter", Alley Cat Allies, accessed July 10, 2014.
- "Feral Cat Veterinary Protocol", Alley Cat Allies, accessed July 11, 2014.
- "Spay and Neuter Clinic Information", Alley Cat Allies, accessed July 11, 2014.
- "Protocols: Eartipping", Alley Cat Allies, accessed July 11, 2014.
- "Rabies: A Public Health Victory", Alley Cat Allies, accessed July l1, 2014.
- "Distemper and Respiratory Virus Vaccines (FVRCP) Protocol for Feral Cats", Alley Cat Allies, Christine Wilford, "Are Vaccines Worth It?", 2009.
- "The Difference between Euthanasia and Killing", Alley Cat Allies, accessed July 11, 2014.
- ACA TNR Guide p. 17, "Post-Surgery", Alley Cat Allies, accessed July 11, 2014.
- NC TNR Guide p. 109. For an example see "A Toronto Rescue Story: Hermione", Youtube user catnip42007, uploaded April 27, 2014.
- ACA TNR Guide p. 18.
- "Safe Relocation of Feral Cats", Alley Cat Allies, accessed July 11, 2014; and NC TNR Guide pp. 127-132.
- "Socialized Cat Guide", Alley Cat Allies, accessed July 11, 2014.
- "Save Lives With Feral Freedom: A Guide to the Feral Freedom Program", Best Friends Animal Society, accessed July 11, 2014. Hereinafter "Feral Freedom."
- ACA TNR Guide p. 5.
- "Post-Surgery", Alley Cat Allies, accessed July 11, 2014.
- "Colony Care Guide", Alley Cat Allies, accessed July 11, 2014.
- Feral Freedom above, first piloted by Jacksonville, Florida. Despite the lack of monitoring, the program reports beneficial effects including far fewer shelter killings, reduced animal control costs, and improved community relations.
- NC TNR Guide pp. 120-124, "Protocols: Testing - Feline Immunodeficiency Virus (FIV) and Feline Leukemia Virus (FeLV)", Alley Cat Allies, accessed July 11, 2014.
- Tabor, Roger (December 8, 1983). The Wild Life of the Domestic Cat. Arrow Books Ltd. p. 224. ISBN 0-09-931210-7.
- Tabor, Roger (April 30, 2003). Understanding Cat Behavior. David & Charles. p. 144. ISBN 0-7153-1589-7.
- Hughes, Kathy L.; Margaret R. Slater (January 2002). "Implementation of a Feral Cat Management Program on a University Campus". Journal of Applied Animal Welfare Science. doi:10.1207/S15327604JAWS0501_2. Retrieved February 14, 2011.
- Levy, Julie K.; David W. Gale, Leslie A. Gale (January 2003). "Evaluation of the effect of a long-term trap-neuter-return and adoption program on a free-roaming cat population". Journal of the American Veterinary Medical Association. doi:10.2460/javma.2003.222.42. Retrieved February 14, 2011.
- Hughes, Kathy L.; Slater, Margaret R. (2002). "Implementation of a Feral Cat Management Program on a University Campus". Journal of Applied Animal Welfare Science 5 (1): 15–28. doi:10.1207/S15327604JAWS0501_2. PMID 12738586.
- Zaunbrecher, KI; Smith, RE (1993). "Neutering of feral cats as an alternative to eradication programs.". Journal of the American Veterinary Medical Association 203 (3): 449–52. PMID 8226225.
- Michael K. Stoskopf and Felicia B. Nutter, "Analyzing approaches to feral cat management-- one size does not fit all," JAVMA, Vol 225, No. 9, November 1, 2004
- Julie K. Levy, David W. Gale and Leslie A. Gale, "Evaluation of the effect of a long-term trap-neuter-return and adoption program on a free-roaming cat population", JAVMA, Vol 222, No. 1, January 1, 2003 
- Trap/Neuter/Release Methods Ineffective in Controlling Domestic Cat "Colonies" on Public Lands
- The Truth About Trap-Neuter-Return and Feral Cat Colony Movement
- LONGCORE, TRAVIS; RICH, CATHERINE; SULLIVAN, LAUREN M. (2009). "Critical Assessment of Claims Regarding Management of Feral Cats by Trap-Neuter-Return". Conservation Biology 23 (4): 887–894. doi:10.1111/j.1523-1739.2009.01174.x.
- Patrick Foley, Janet E. Foley, Julie K. Levy, "Analysis of the impact of trap-neuter-return programs on populations of feral cats," JAVMA, Vol 227, No. 11, December 1, 2005
- Jim Sterba (13 November 2012). Nature Wars: The Incredible Story of How Wildlife Comebacks Turned Backyards into Battlegrounds. Random House Digital, Inc. p. 259.ISBN 978-0-307-98566-8. Retrieved 11 April 2013.
- "Humane Cat Population Management Guidance" - report of International Companion Animal Management Coalition to help governments worldwide address community cat populations in a humane manner, includes TNR.
- "Alley Cat Allies" - Website offers vast array of links and publications with practical information about TNR and community cats; for veterinarians, shelters and community members.
- "How to Help Feral Cats: A step-by-step guide to Trap-Neuter-Return" - Many practical tips on TNR, prepared by Alley Cat Allies in 2009 and updated in 2002.
- "Cats & the Environment Resource Centre" - Science of cats and wildlife (especially birds), setting the record straight, links to resources provided by Alley Cat Allies.
- "Neighborhood Cats" - TNR organization in New York city, provides many resources online and otherwise about TNR and community cats: news updates, tools, webinars, videos, legal info: Model TNR Ordinances now available from Neighborhood Cats; TNR handbook (link below).
- "Neighborhood Cats TNR Handbook: The Guide to Trap-Neuter-Return for the Feral Cat Caretaker", Bryan Kortis et al, Neighborhood Cats, 2nd edition, 2013. Comprehensive guide to TNR, 162 pages. OK to print/distribute except in New York city, where copyright requires getting copies from Neighbourhood Cats.
- "Feline Shelter Intake Reduction Program FAQs" - Maddie's Institute, January 2013 article on community cats. Other articles on feral cats: "Feral/Community Cats Articles". Organization based in Pleasanton, California, supports research on helping feral cats and shelter animals, and provides funding for TNR and spay/neuter programs.
- "What You Can Do To Help Feral Cats", Humane Society of the United States, July 3, 2013, accessed June 20, 2014. Resources for individuals, organizations and public officials.
- "Feral Cats FAQ", ASPCA, accessed June 20, 2014. Extensive resources, answering questions from what is a feral cat, to how can I keep feral cats out of my yard, to how can I become a colony caretaker, and more.
- "Vox Felina", blog "Providing critical analysis of claims made in the name of science by those opposed to feral/free-roaming cats and trap-neuter-return"
- Trap Neuter Return, TNR information from Stray Cat Alliance, organization based in Los Angeles, California.
- "Alley Cat Rescue" Some links on feral cats and TNR topics from organization based in Mount Ranier, Maryland.
- "What is Trap-Neuter-Return" - Animal Coalition of Tampa's Project Spay Day.
- ca-r-ma.org, a Canadian organization fostering TNR via a system of community based affiliated groups throughout the Maritime Provinces.
- What is Trap-Neuter-Return (TNR)? - TNR info by Forgotten Cats, Inc., of Greenville, Delaware.
- Information on Managed Cat Colonies and TNR - criticism of TNR by American Bird Conservancy.