Realizing New Possibilities
through Non-Surgical Solutions


Webinar on 6/8/20: What computer modeling can tell us about what to expect from a COVID-19 TNR sterilization gap

Webinar Title Screen
Panelists in this webinar, hosted by Stacy Lebaron of The Community Cats Podcast, discuss ACC&D’s computer simulation modeling of free-roaming cat populations and the impact of a COVID-19 gap in sterilization surgeries on trap/neuter/return (TNR) scenarios. Panelists include members of ACC&D’s modeling committee: ACC&D’s Joyce Briggs, wildlife population biologist Dr. John Boone, and the ASPCA’s Dr. Margaret Slater, as well as Peter Wolf, research and policy analyst for Best Friends Animal Society.

Note: This webinar discusses the ACC&D video “Keep Calm and Carry on: The Impact of COVID-19 on TNR and How to Get Back on Track.” Please watch the video before viewing this webinar discussion panel.

Watch a recording of the webinar here.

Population Dynamics of Free-Roaming Cats: Managing Outdoor Cat Colonies to Meet Your Goals

An ACC&D Flagship Initiative


How many free-roaming cats do we need to reach to stabilize, reduce, or eventually eliminate a specific population?

Trap-Neuter-Return (TNR) programs certainly benefit the cats that they reach. However, many involved in TNR programs ask this question as they set goals and strive to reduce numbers of cats at the colony or community level. ACC&D is working to answer this question, and has created tools to help you achieve the most from your TNR efforts. 

What difference can a multi-year contraceptive make?

This question is a critical one for ACC&D. We are striving to understand if an affordable, multi-year contraceptive, able to be applied in the field, could be a useful tool for TNR programs. In the course of our research, we discovered that a lot isn't not understood about how to achieve the greatest impact with surgery-based TNR. We assume that permanent sterilization (surgical or non), removal of animals, and multi-year contraceptives will have different impacts. We know that free-roaming cats have, on average, much shorter lifespans than pets–so just how long must fertility control last to benefit a colony of cats?

Using computer modeling to find answers

The wildlife field uses sophisticated computer software to model wildlife populations (Vortex). We convened a team to use Vortex software and develop a feline population model to better understand the dynamics of free-roaming cat populations over time. The team includes experts in wildlife conservation, free-roaming cat welfare, feline behavior, and TNR.  

In 2013 and 2014 we combined field research data with modeling outputs to develop the most comprehensive feline population model available to date. This computer modeling has provided a wealth of data that we continue to analyze and publish findings about. 

In November 2014, “Simulating Free-Roaming Cat Population Management Options in Open Demographic Environments,” was published in the peer-reviewed, open-access journal PLOS ONE. The study estimates the percentage of cats that must be reached by different methods to achieve different goals. For a summary of the results, read our press release.

Cumulative Preventable Deaths over 10 yrs In July 2019, we published A Long-Term Lens: Cumulative Impacts of Free-Roaming Cat Management Strategy and Intensity on Preventable Cat Mortalities, which revealed that high intensity sterilization of free roaming cats reduces populations with the least preventable deaths of cats. These findings indicate that over a 10-year period, free-roaming cat populations managed using high-intensity Trap-Neuter-Return (TNR) not only reduced population sizes, but also that such populations experienced over 30 times fewer preventable cat deaths over the same period, compared to taking no action. The study, which was published in the peer-reviewed open-access journal Frontiers in Veterinary Science, can be found here.

TNR Cats -Covid-19 COVER SLIDEIn May 2020 with the world facing a global pandemic, ACC&D’s computer modeling experts built on our prior published work to simulate the impact of a COVID-19 gap in sterilization surgeries on different trap/neuter/return (TNR) scenarios. Results show that TNR work to date, and the presence of sterilized cats in the colony, can be a really good investment, and that ground that is lost will not be as hard to regain, as it might seem.

Our modeling work also revealed how programs can be most successful when resuming TNR. To learn more, watch the video, Keep Calm and Carry On: The impact of COVID-19 on TNR and how to get back on track.

Our Guidance Document translates model findings into guidelines for cat management programs. And, because you can only evaluate impact when you know your starting numbers of cats and measure population change over time, we’ve also created a How-To Guide to counting cats and monitoring cat population numbers to evaluate intervention impact. 

For additional information about ACC&D's cat population modeling work click on the menu below. ​

Research & Innovation


News & Updates

Thank You to the ASPCA for funding this Flagship Initiative, to Boehringer Ingelheim Animal Health for providing support for the economic modeling phase of the project, and to the many experts who have volunteered significant time and energy on this project.



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