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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 make a difference for the cats that they reach. However, the question above is one that many involved in TNR programs are asking as they set and strive to achieve goals to impact the population of cats at the colony or community level. ACC&D has worked to answer this question, and to create tools to help you get the most from your TNR efforts. For the full story, see below, but here are some quick links to get you started:

ACC&D-created resources:

A study confirming that free-roaming cat populations can be reduced by fertility control if performed at sufficiently high density  and a companion guidance document briefly summarizing key findings and their practical application for managing free-roaming cat populations

A “how-to” guide to “counting cats”

Other resources:

Relevant Literature

We are currently preparing additional relevant manuscripts for publication that we will share here once published so be sure to check back! 

"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. We discovered that there is a lot that’s 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?

We learned that the wildlife field has more sophisticated software than has been used before to understand cat populations. So we convened a team (see below) that includes experts in wildlife conservation, free-roaming cat welfare, feline behavior, and TNR.

Timeline of ACC&D’s Free-Roaming Cat Population Dynamics Flagship Initiative

In 2013 and 2014 we worked to combine field research data with sophisticated computer modeling software to develop the most comprehensive feline population model available to date. 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. (Our press release summarizes results.)  

Our Guidance Document translates model findings into guidelines for cat management programs. And because it is hard to evaluate impact without knowing how many cats you are starting with or measuring change over time, we’ve also created "how-to" guide to “counting cats” and monitoring cat population numbers to evaluate intervention impact.  

And we’re just getting started! We are currently working on a second phase of modeling that will look at combination approaches to free-roaming cat population management (e.g., removing social kittens for adoption or combining surgical sterilization with long-term contraception) and fold in the economic costs of different strategies.

We’ll also be looking for your participation to help improve the model! If you have a well-run TNR program and are hungry for ways to better measure and evaluate your impact, please read the materials above and then contact us at about getting involved.

The ACC&D Free-Roaming Cat Model Development Team:

  • Aaron Anderson, PhD * National Wildlife Research Center, USDA APHIS
  • Valerie Benka, MS, MPP * Alliance for Contraception in Cats & Dogs
  • John Boone, PhD * Great Basin Bird Observatory
  • Joyce Briggs, MS * Alliance for Contraception in Cats & Dogs
  • Dennis Lawler, DVM, FNAP * Illinois State Museum, Pacific Marine Mammal Center Laguna Beach
  • Julie Levy, DVM, PhD, DACVIM * University of Florida College of Veterinary Medicine
  • Philip Miller, PhD * IUCN/SSC Conservation Breeding Specialist Group
  • Felicia Nutter, DVM, PhD, DACZM * Tufts University
  • Margaret Slater, DVM, PhD * ASPCA
  • Chris Slootmaker, PhD candidate * National Wildlife Research Center, USDA APHIS 
  • Steve Zawistowski, PhD, CAAB * ASPCA (retired)

Our thanks 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 (listed above) who have volunteered significant time and energy on this project.

    Boehringer Ingelheim logo

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