7.2.1 Modeling TNR

To best apply TNR, simulation modeling of cat populations has continued to become more sophisticated. One study examined the number of “preventable cat deaths” based on various intensities and types of removal and TNR (Boone et al. 2019). Preventable deaths included removal for euthanasia as well as kittens born who ultimately died. Removal for euthanasia of 25% or 50% of all cats every six months as well as removal of 25% or 50% of cats in a six‐month period followed by doing nothing until the population had rebounded (modeling the “culling” of cat populations) were four of the options. In these 10‐year simulations of a 50‐cat population, doing nothing led to the greatest number of preventable deaths, closely followed by removing 25% or 50% of cats for euthanasia in a six‐month period then doing nothing until the population returned to capacity before removing cats again. Even more compelling was that doing TNR on 25% of the intact cats every six months resulted in more preventable deaths than removing 50% of all cats every six months for euthanasia. Overall, the number of preventable deaths was greatest for doing nothing (~1,000 cats/kittens), followed by both levels of removal for euthanasia and rebound, then removal for euthanasia at 25%, 25% TNR, 50% removal, and finally 75% TNR (32 cats/kittens).

Modeling suggests that effective TNR in the real world likely requires about 75% of intact cats be sterilized every six months to decrease the population over time and minimize the number of preventable deaths (Boone et al. 2019). This means that it is critical to define a cat population small enough to trap, sterilize, and return 75% of intact cats every six months. Performing intensive TNR up front results not only in faster and greater population declines but also fewer kittens born who then die.

Building on intensive TNR, Benka et al. (2021) examined the cost of various scenarios using price estimates from programs around the country. When TNR was done by trapping and sterilizing about 75% of intact cats every six months, the population decline in 10 years was comparable in cost to the 25% removal for euthanasia. TNR at this intensive level led to relatively small numbers of cats remaining intact to be trapped, with the actual number being dependent on the magnitude of immigration or abandonment. Fewer cats trapped means lower costs compared to removal for euthanasia, where 50% of ALL cats need to be removed every six months. Analysis of costs for TNR demonstrated that trapping costs were a small component of total cost—hiring someone to trap so that higher intensity, front‐loaded TNR is not a cost barrier in the long term.

7.2.2 Counting Cats

If a goal is population decline, the relative numbers of cats across time and the density of cats in a community need to be known (Boone 2015). Then, intelligent management programs can be designed, success documented, and work adjusted as needed to track the impact of TNR. One major new initiative is the DC Cat Count, a collaboration of organizations working to create new knowledge about valid methods for the best ways to count cats (DC Cat Count 2018). This collaboration will develop tools to help animal shelter staff, volunteers, citizen scientists, and students determine just how many cats there are in a given geographic area.

The two main ways to count cats are using cameras and/or walking routes. The optimal placement of cameras to “trap” pictures of community cats has been studied and still needs refinement (Read et al. 2015; Carter et al. 2019; Nichols et al. 2019; Taggart et al. 2019). A Canadian study described how to create random walking paths (transects) in a city using primarily existing streets (Hand 2019). The author noted that this type of count could provide changes in cat population density over time when consistently repeated as well as identify specific locations with high cat populations, making targeting of interventions more feasible.

Geospatial mapping has been applied in New Zealand to predict locations of community cats. Individuals and groups of cats from TNR records were mapped. These locations were predicted by human population density, landscape characteristics, and socioeconomics in this region (Aguilar et al. 2015). Additional research is needed to determine if these variables are predictive in other geographical locations.

7.2.3 Recent Community Cat Management Research

A newly appropriated methodology in the study of cats is citizen science, a method of integrating outreach with data collection via the use of non‐scientist volunteers (Cooper et al. 2007). It is cost‐effective; however, its main value is that it permits coordinated, consistent data collection over time and larger geographies so trends can be studied. The use of trends makes the potential biases, such as lack of consistency by some observers, varied ability by observers to visualize cats, or a tendency to find cats in locations where there are more cats visible or active, less problematic. A study that used middle school and undergraduate students to collect data across a wide geography determined that cats and coyotes didn’t share space except in small urban forest areas. Green spaces were found to have many coyotes and few cats (Kays et al. 2015). Instead, cats were found primarily in residential yards.

An urban Illinois resident developed a citizen science project and generated a rich TNR data set that led to important discoveries (Spehar and Wolf 2018). Between 2007 and 2016, 20 locations within a 1 km² area contained 195 cats who underwent TNR (92%) or were adopted. Of these cats, 30% were initially or eventually adopted, 34% disappeared, 7% died, 3% were euthanized due to serious injury or illness, 2% were returned to their owners, and 1% moved outside of the area. Peak group size within the area occurred within the first two years of starting management (from 1 to 35 cats). By 2016, only 44 total cats (23%) remained, with eight groups eliminated. The largest group decreased from 35 cats to 12 cats; all other groups ranged from 1 to 6 cats. These data illustrate the importance of ongoing efforts across longer periods to see population size impacts from TNR.

An indirect way to demonstrate the impact of TNR is surveys of caretakers. In Australia, where cats are particularly contentious, TNR is generally considered to be illegal, although the laws vary by state and local government (Rand et al. 2019). Adults involved in TNR in Australia were surveyed using an anonymous online tool (Tan et al. 2017). While this approach likely included only the most motivated and successful caretakers, the results demonstrate that a reduction in cat group size appears possible. For the 21 groups of cats with good data, the median initial group size was 11 (ranging from 3 to 40 cats) and declined over a two‐year period to a median of 5 cats. There was variability in the trend for number of cats, with 17 groups becoming smaller, 4 groups staying the same, and 1 getting larger, as has been documented in other studies. Adoption was used in most but not all groups to decrease the population size; in some locations more than 50 cats and kittens had been removed. More than half of the groups had all adults sterilized, with the lowest sterilization at 47%. More respondents reported involvement in feeding and seeking resources for the cats than in trapping or transporting to the veterinarian, important findings when developing a program and identifying needs. A surprisingly high percentage of respondents indicated they provided treatments for fleas and intestinal parasites (69% and 73%, respectively) indicating that this could be a more common health service if the caretakers were made aware of its importance and provided with cost‐effective products.

A more recent Australian survey of 30 residents involved in TNR reported that nearly all became involved out of a desire to effectively reduce cat populations over time and over concern for welfare and humane management (Rand et al. 2019). Seven respondents reported that they got involved because a friend or acquaintance asked them to, a potentially underused mechanism of engagement in TNR for other locations. Caretakers often received permission and sometimes support from police, housing representatives, or residents. Complaints were most commonly from neighbors, and attempts to resolve them were successful about half the time. These studies illustrate both the drive for people to help as well as the need for more options to manage cats.

Cat caretakers are key stakeholders whose trust can be difficult to gain when planning or implementing TNR. However, their wealth of information about the cats makes it worthwhile to make every effort to engage them, particularly those caretakers of larger groups of cats (Gunther et al. 2016). When working with caretakers, it is important to recognize that they often experience emotional stress and inability to afford treatment when caring for their cats (Young and Thompson 2019). TNR organizations can provide positive connections to other caretakers and organization members to help mitigate disillusionment, cynicism, and burnout.

The one element of managing cats with the least amount of research is stopping new cats from leaving the owned population and becoming community cats. Sterilizing owned cats as well as keeping owned cats in their homes are critical approaches (Miller et al. 2014). Substantive work in this area would be extremely valuable since immigration, including abandonment, continues to be a problem. In one example, a study in Canada identified 18 groups of cats around barns and stables with an average of 14 cats per group (Bissonnette et al. 2018). Ten groups of cats were intensively trapped for 48 hours and sterilized. The investigators were able to trap between 67% and 100% of cats in each group, with 90% median sterilization at 7 and 12 months of follow‐up. In this short study, the original cats tended to leave and more new cats to enter the intact groups than the sterilized ones. In an urban example, cats in New York City also demonstrated very high turnover rates, from 78% to 98% (Kilgour et al. 2017).

Quite a few new articles on the impact of TNR on population size have been published. In Newburyport, Massachusetts, a 17‐year program that included the creation of a limited‐admission cats‐only shelter, engagement of business owners, organized twice‐daily feeding, and experienced cat trappers resulted in the elimination of approximately 300 cats (Spehar and Wolf 2017). TNR and the removal of socialized cats and kittens resulted in rapid population decline. These efforts, coupled with prompt, accurate identification of new cats, supported the eventual elimination of the population. This program is notable for how visible and comprehensive it was as well as how much the members of the group learned and problem solved. They used media coverage, tabling, and tours of the shelter to explain the work to the community—beginning in the early 1990s when little was known about TNR. Initially envisioned as solely TNR for unsocialized cats along the waterfront, it soon became evident that many of the cats were socialized. This led to two notable decisions: that adoption needed to be part of the solution and that these socialized cats were likely coming from residents who didn’t feel they had a place to take cats they couldn’t keep. They also learned that cats living in groups for years sometimes became adoptable (Spehar and Wolf 2017; Swarbrick and Rand 2018). Some could be rehomed with their caretakers. By 2009, the last cat died at the age of 16.

TNR success at population control was also studied at the community level. A long‐term program’s records from a gated community in Florida were used to estimate population size, change in population, cat outcomes, feline leukemia virus (FeLV), and feline immunodeficiency virus (FIV) prevalence across 23 years (Kreisler et al. 2019). This program began in 1995 and in 2006 added an adoption facility, sanctuary, and veterinary clinic. Again, it was clear that ongoing efforts were needed for a successful program managing more than 2,500 cats over the years. There were 1,111 cats returned and 1,419 were removed: 711 (50%) for adoption, 441 (31%) euthanized for FeLV‐ or FIV‐positive tests, and 209 (15%) reported dead as part of the efforts to track cats; 58 (4%) died in care. Over 23 years, the number of cats estimated to be in the community declined from 661 cats to an estimated 83 cats in 2017. The average age of cats was about 7 years in 2006 with a decline to about 4 years in 2017. The prevalence of cats positive for FeLV or FIV also declined over time. This was a highly visible program within the gated community. The controlled access was believed to have decreased casual abandonment of cats, but there were many seasonal residents and staff who could have accounted for the continued arrival of new cats.

In Rome, data on cat sterilization was obtained across a 30‐year period through 2018 (Natoli et al. 2019). Italy is a country where TNR has long been practiced, in some locations such as Rome, with government support. Groups of cats newly registered each year peaked in 2011 at about 160 after a city project to provide free sterilization for owned cats and have declined to about 80 in 2017. Of these groups of cats, 204/1,878 had stabilized their size and 89 gone extinct.

University campuses are different types of communities. In a 28‐year follow‐up of a university campus program in Florida, the original 204 cats declined to 10 (5%) and the 16 feeding locations to five (Spehar and Wolf 2019a). This was in the face of expanding student enrollment. The majority of new cats were seen in the first 10 years of the program. At first appearance, 43 socialized cats and 161 unsocialized cats were found. After 28 years, 45% of cats had been adopted, 24% disappeared, 11% were euthanized (for severe illness or injury or testing positive for FeLV or FIV in the early program years), 8% died, and 6% were known to have moved off campus. Cats who died or were euthanized had the longest median time on campus of 4 years, with one cat living 14 years. Factors that led to success were keeping a low profile for the program and having feeding stations in inconspicuous locations to discourage abandonment of cats as well as the university’s “no pets” policy. The vigilance of caretakers in monitoring for new cats also contributed to sustained reductions long term. Clearly, this success required ongoing commitment, time, resources, and dedication but was possible!

A nine‐year university program in Australia also was able to show substantial declines in cat population over time (Swarbrick and Rand 2018). This program began with a pest control company hired to trap and euthanize cats. In contrast to the program described in the previous paragraph, this was a very public activity. A key element for success was beginning as a one‐year trial or pilot, having very explicit and population‐oriented goals, holding regular meetings, and keeping good records. They also used feeding rosters, so the daily feedings were consistently done in inconspicuous feeding stations. During the program, 122 cats were handled, with 30% adopted or returned to their owners, 30% died or were euthanized, and 29% disappeared. Because the program actively encouraged reporting of any new, ill, injured, or deceased cats, the records were able to provide some additional details. Causes of death were accidents (5/14), serious diseases (4/14), one death during surgery, and four unknown. The most common reasons for euthanasia were cancer and renal disease (80% of euthanasia). An 8% per year mortality rate was calculated and was consistent with two other pet cat populations (New et al. 2004; O’Neill et al. 2015). The population on campus declined from a high of 69 at the beginning of the program to 15 adult, neutered cats in 2017, a 78% reduction in population size.

7.2.4 Community Cat Welfare

The question of welfare among community cats in light of deaths due to being hit by cars or “disappearances” continues to depend on one’s values and beliefs. Recent discussions identified freedom from injury and disease, affective state (positive and negative feelings), and being able to behave naturally in the animals’ environment as key considerations (Fraser 2008). TNR appears to support the first criterion. The last criterion is arguable: Is the lack of parenting and sexual behaviors a loss of “natural” behaviors? Of course, but so is less fighting and roaming leading to less injury and illness. And there are certainly short‐term negative experiences from the TNR process (including trapping, transportation, injection of anesthetic, and overall stress) to weigh against better health. While these types of discussions are beginning, we are unlikely to come to consensus since we cannot ask the cats. Pragmatically, cats who could be adopted and removed from these risks presumably would have better welfare as pets. Remaining feral cat options are preemptive euthanasia, TNR, removal to a new environment with unfamiliar cats and people (a sanctuary), or doing nothing. Better knowledge of community cat welfare could help support which options might lead to the best welfare for a particular cat.

A newly developed cat welfare scale could be valuable for evidence‐based best practices for cats. This promising tool used a simple visual scale for owned, managed (with a caretaker), and unmanaged (no caretaker) cats to assess their welfare (Zito et al. 2019). The visual scale included body condition score (9‐point scale), coat condition, nose and/or eye discharge, ear crusting, and injuries (all a 4‐point scale). The majority of cats in all three groups had ideal body condition, good coats, and no indicators of illness or injury. The authors suggested that this scale could be validated against hands‐on examination and potentially blood work.

Another recent study in Austria added criteria to evaluate welfare including overall behavior, salivation, and general impaired health (Gilhofer et al. 2019). Five groups had from 12 to 30 cats; the remaining eight groups ranged from 1 to 9 cats; all had varying levels of sterilization. The presence of fewer clean feeding places was associated with more thin or apathetic cats (presumed ill) even when most cats were in good body condition and healthy. Cats approached caretakers who offered treats or diluted milk more closely (within 0.5 meters) than caretakers who did not. There was good to excellent agreement between the two observers, which meant that the criteria used may be reliably scored by different people.

In Israel, the welfare of cats in a city with TNR was evaluated by similar criteria (body condition score, visible illness or injury, and skin disease) (Gunther et al. 2018). Cat welfare was determined by walking transects through the city during a three‐year period with 4,615 cat sightings. Among cats seen, 62% were sterilized and, within the 26 city neighborhoods, sterilization rates ranged from less than 20% to greater than 70%. In this city, kittens were significantly more likely to be emaciated and have severe injuries. Sterilized adult cats were more likely to be obese and less likely to have skin lesions than intact adults. These sterilized adult cats were more likely to have a permanent disability like missing an eye, tail, or leg; this was attributed in part to their potentially longer life span than intact adults. A new finding was that having a higher proportion of sterilized cats in the surrounding areas decreased the prevalence of emaciated or thin adult cats (intact or sterilized). The reasons for this weren’t known but could have been related to decreased aggression and/or competition following sterilization.

7.2.5 Recent Shelter Intake and Community Cat Research

Intensive sterilization within small locations is generally considered to be necessary when decreasing shelter intake is a goal. The impact on shelter intake maybe be due to (i) the level of sterilization being high enough to decrease the cat populations, (ii) more owned cats being sterilized, and (iii) changing community awareness and philosophy about cats. In Chicago, TNR was performed in two zip codes from June 2011 to June 2013 with about 1,500 cats sterilized and 23% being removed for adoption (Spehar and Wolf 2018). There was a 30% to 40% reported reduction in intake from those zip codes attributed to this effort. The following two years, two more zip codes were added, about 2,000 cats sterilized, and similar results reported. These researchers attempted to account for other potential reasons for intake decline since intake data can be influenced by a variety of factors beyond TNR.

Another study targeted one large zip code (12 km²) in Florida and aimed to trap at least 50% of the estimated population (based on survey findings) for return or adoption to decrease shelter intake (Levy et al. 2014). Over two years, 2,366 cats were trapped (a trapping rate of about 60 cats/year/1,000 residents), 52% returned, and the remainder adopted or transferred for adoption. Shelter intake from the targeted zip code decreased by 66%. By comparison, shelter intake outside that zip code had increased at the end of the study. Animal control officers also shifted from immediate impoundment to sharing information and connecting residents with other resources, a critical component.

Among six municipal shelters where TNR and RTF were implemented, four of these communities saw substantial decreases in cat intake after three years compared to the baseline year before the programs began (Spehar and Wolf 2019b). All reported a greater than 67% decline in feline euthanasia/1,000 residents and increases in live release rates for felines of 74% or higher. The median reduction of feline intake was 32%, with a median decline in euthanasia of 83%. The live release rate increased a median of 53%. Between 8% and 24% of cats in those programs were adopted or transferred for adoption. Only 0.3% to 1.1% of cats were ill enough to die or require euthanasia, supporting the overall good health of the cats.

The number of cats undergoing RTF was about 14,000 for all six of these communities (Spehar and Wolf 2019). That is a relatively small number compared to the aggregated intake of about 54,000 felines (about 26%) and not enough to be solely responsible for the 53% increase in live release rate. The number of households in the six communities was about 2.2 million based on US census data. Assuming 11% of households feed cats and multiplying by four for an estimate of numbers of cats, that equates to just under a million cats (Levy et al. 2014). Therefore, total surgeries of about 73,000 was 7% of all cats. That is a relatively small proportion and seems unlikely to have resulted in a reduction in the cat populations in those communities and subsequent reduction in intake numbers. Other factors are likely implicated in the reduction in euthanasia as well as intake.