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Methods & Metrics
The best policies and programs are those that are shown by data to be proven effective at doing the things they claim to do. Rigorously testing what works best helps a field move forward (and save more lives). There is broad public support for using spay/neuter programs instead of culling to manage free-roaming cat populations, and there is peer-reviewed research that these spay/neuter efforts can correlate with decreases in shelter intake, lower shelter euthanasia of cats, and reduced cat nuisance complaint calls. However, there is little evidence one way or another as to whether spay/neuter programs can reduce the size of cat populations.
Those who are involved with spay/neuter programs believe that their work is reducing cat populations. It's easy to find people in cat welfare circles who can tell you about their personal experiences over years or decades of trapping cats and taking care of cat colonies while watching populations decline or even disappear over time. Although these oral histories are compelling to cat advocates, personal stories aren't scientific evidence.
Most of the spay/neuter research published by veterinarians and animal welfare professionals focuses on the metric that is most important to cat lovers: reducing the deaths of cats. However, for those who oppose using spay/neuter programs and push for widespread culling of cats, reducing cat deaths is not the issue that matters to them. Metrics championed by cat advocates as proof that spay/neuter programs work – decreases in shelter intake, lower shelter euthanasia of cats, and reduced cat nuisance complaint calls – are often viewed by cat advocates as evidence for cat population decreases. Fewer cats entering animal shelters could mean that there are fewer free-roaming cats outdoors, or it could simply mean that a given shelter changed their intake policies.
The reduced intake of cats to animal shelters is an indirect possible metric of a decrease in free-roaming cat populations, as is a decrease in shelter euthanasia or cat-related complaint calls to animal control. Whereas this type of data is easy to obtain and track over time – and it's better to track these metrics than nothing at all – there is a need for better tools for monitoring a direct metric of the number of cats on the outdoor landscape. Of the ways that one can conduct an impact assessment of a spay/neuter program, this is the most difficult thing to study. Few people in cat welfare and veterinary worlds know about methods to quantify populations of free-roaming animals. Wildlife researchers and population ecologists, however, have an array of methods to do so.
Using Wildlife Research Methods to Study Cats
Is Kitizen Science a study in veterinary medicine?
No. We use methods from wildlife population ecology, a different field.
Veterinarians generally focus on individual-level biology: genetics, cellular biology, physiology, and an individual animal's health and welfare. Veterinary education includes some training in epidemiology – the study of disease in populations of animals – but this is mostly limited to meat safety in animal agriculture operations and controlling zoonotic diseases like rabies. Veterinarians are great at what they do and integral to the world of animal welfare, but they don't have the training to quantify and monitor population sizes of free-roaming animals.
Population ecologists are wildlife researchers that focus on groups of animals and the size and dynamics (changes in size) of a population. They can't diagnose an animal with a medical condition or provide treatment the way a veterinarian can, but a population ecologist can study questions that involve animal reproduction, behavior, migration, or adaptations to living near humans, such as, "How many offspring do coyotes produce in the suburbs of California versus the wilds of Alaska?"
If you operate a spay/neuter program, you may have heard that you can roughly estimate the cats in an area by taking the human population and dividing it by some number. That's a good way to make a ballpark guess at how many animals your program might serve when you are applying for your first grants, but this ratio method is not meant for conducting a scientific population estimate or monitoring changes in cat populations over time.
Unless you are working in a small, contained area like an RV park where you can conduct a true census (identify every single cat), it is not possible to count all the cats in a large area. Cats aren't trees: they move and hide, and won't line up and sit still to be counted. So, how can we track the number of free-roaming cats in an area if a census isn't possible?
Thankfully, there was no need to reinvent the wheel. Assessing an animal group's size is one of the fundamental tools of a wildlife population ecologist's toolkit. This is how conservation researchers estimate things such as the remaining population sizes of threatened and endangered species.
Mark-Recapture Population Estimation
Kitizen Science learned from decades of research on wildlife population estimation to create a first-of-its-kind photographic mark-recapture system (also referred to as photographic mark-resight or photographic capture-recapture) that works at the perfect middle ground of being highly scientifically rigorous but still simple enough for volunteers to do.
Think back to the problem preventing us from conducting a cat census: cats move around. While this might seem like a barrier, it is actually the thing that makes photographic mark-recapture work. Fifty years ago, mark-recapture would mean physically capturing some animals in a population, marking them in a visible way, releasing these animals to mingle with others, capturing some members of this population again, and counting how many were previously marked. From that information, you can estimate how many animals are in the larger population. Here is a simple example: you trap 20 cats and spray them with green dye, then set them free to move around in the local cat population. The next day, you come back and trap 20 cats again, and 10 out of 20 of these cats were dyed. From that, you can infer that there are about 40 cats in the area, since it appears that the 20 cats you sprayed with dye make up about half of the population.
Mark-recapture population estimation today involves more variables and a lot of complicated statistics, but this example conveys the basic principle on which those methods are based.
Kitizen Science uses photographic mark-recapture because it does not require stressful capturing or handling of animals. Instead of a cat being "marked" physically, it is "marked" by being identified as a unique individual based on its natural coat patterns. (Animal welfare is a top priority of Kitizen Science, and our research methods are completely non-invasive. The cats being studied don't even realize it!) Not all cats in an area need to be uniquely identifiable, such as solid black cats.
Citizen Science
Finally, we chose to be a citizen science project, which are set up to bring together researchers and a community to study a topic of interest by involving volunteers in roles such as data collection and data organization. These projects not only reduce the cost of conducting research, but also engage the public in the scientific process around issues that matter to them. Many of the largest and longest-running citizen science programs are about monitoring songbirds (like the Christmas Bird Count), but the citizen science framework is also used to learn about a variety of other issues: exploring astronomy, folding proteins, tracking the decline of bees and insects, testing air and water quality, studying coral reef bleaching, timing when wildflowers bloom, and more.