Bella, rescued from the high-kill Carroll County Animal Shelter in Georgia.

The science of population dynamics teaches us that there are really only four factors that influence the size of a population of animals or plants. They are birth rate,death rate,immigration and emigration.

The birth rate is simply the number of animals born in that population in a given time period. The death rate is the number dying in that same time period. Immigration is the rate at which animals join the population in question from some other population. Emigration is the rate at which animals leave the population in question for some other population.

The maximum sustainable size of a given population is governed by the habitat’s carrying capacity. The carrying capacity is determined by limiting factors—resources such as food, water and shelter.

Population biologists refer to groups of interacting populations of a given species as a metapopulation, basically a ‘population of populations’. They interact by exchanging members through immigration and emigration. Each of these interacting populations within a metapopulation is called a subpopulation.

Why the science lesson in a column about animal welfare? Simple—looking at the pets in a given community as a metapopulation can help us see how to save all the healthy and treatable pets in that community. A community’s pets can be divided into three subpopulations. There are pets with homes and pets without homes. These twosubpopulations interact and exchange members. Pets with homes can join the ranks of the homeless when they are lost or abandoned. Pets without homes can get homes when they are found, rescued or adopted. This exchange process often involves an animal entering the third subpopulation of pets in a community—those in its shelters and rescue groups.

Entering this third subpopulation has traditionally proved deadly for animals because shelters have long relied on the death rate as a means of controlling the size of this subpopulation. While there has been much talk about spaying and neutering*, which curbs the birth rate, it is only fairly recently that some shelters have begun spaying and neutering all adopted pets. Many still adopt out unaltered animals, sometimes relying on contracts or monetary deposits to induce adopters to have the pet altered by their own veterinarian after adoption. This is an unwieldy system guaranteed to have some level of non-compliance, resulting in the system’s failure. The traditional model of animal sheltering has failed miserably because it simply does not address the four factors which influence the shelter pet population in a comprehensive or meaningful way.

“Wait a minute, there is a pet overpopulation problem!”, you say. “There are more pets entering shelters than there are homes for them. The number of pets exceeds the carrying capacity for pets. There simply aren’t enough homes for them all. The number of homes is the limiting factor.”

“Not so!”, says Nathan Winograd, author of Redemption: the Myth of Pet Overpopulation and the No Kill Revolution in America. “Not so!” says Maddie’s Fund,  the actual data indicate otherwise. There are 17 million people in this country who are looking to acquire a dog or cat this year, but haven’t yet decided from where—the ‘swing voters’ . About 8 million animals will enter shelters, and of those, about 4 million will be killed. Of those 4 million killed, about 90% are healthy or savable. Therefore, there are 17 million potential homes for fewer than 4 million animals. Homes are not a limiting factor. Pet overpopulation, far from being received wisdom, is in fact, a myth, and a deadly one. It has too long served as a smokescreen for the real reason why the death rate is used to control the shelter pet population—the habit of institutionalized uncaring in the shelters themselves.

Enter the No Kill Equation, the first and only proven method for saving all healthy and treatable animals in a community’s shelter pet population. It succeeds by comprehensively addressing the shelter pet population using the three non-lethal factors which influence any population. With the NKE, shelters are restored to the original and proper definition of the term—places of safety for animals. Euthanasia too is restored to the original and proper definition of the term, and is used only for those animals who truly are irremediably suffering or vicious. The NKE has 11 points. Let’s have a look at each one.

Trap-Neuter-Return for feral cats is an integral part of the No Kill Equation.

1. Feral cat TNR Program: Also known as ‘Trap, Neuter, Return’, TNR keeps feral cats out of the shelter pet population. Feral cats, called ‘community cats’ by some, have homes. They live outside, on their own and don’t belong in shelters. They grew up without being socialized to humans and can’t be adopted into human families. Volunteer caretakers feed and monitor feral cat colonies. They humanely trap the cats and have them spayed and neutered, then return them to their habitats and continue caring for them there. This controls the birth rate. When new cats immigrate into the community’s population, they can be TNRed as well, or adopted into homes if not really feral. The immigration rate is lower than with the traditional ‘catch and kill’ method of dealing with feral cats, however, because with TNR, the niche occupied by cats is not left vacant—cats are territorial. The ‘catch and kill’ method perpetuates a never-ending cycle of killing. It is also more costly than TNR, which relies largely on the volunteer labor of caring community members. Over time, managed colonies shrink as the cats live out their life spans.

2. High Volume, Low Cost Spay/Neuter: By making spay-neuter readily available to the pets of all members of the community, the birth rate in the overall pet population is effectively curbed, reducing the number of animals entering the shelter population (immigration). Studies, including the recent Petsmart study, indicate that a major obstacle to spay-neuter is the cost of the surgery. Low cost clinics reduce the number of animals entering shelters. Punitive laws, such as mandatory spay-neuter, or MSN, actually increase the number of pets entering shelters.

3. Rescue Groups: By working with rescue groups, a shelter reduces its population through emigration—the animals leave the shelter to go into rescue and ultimately into homes. The number of animals between homes is not limited by the four walls of the shelter building. Members of the community pitch in. Lives are saved. Remember the responsible public–that previously ignored stakeholder?

4. Foster Care: Once again, by relying on the responsible public, this time with a comprehensive foster care program in which all orphaned kittens and puppies, sick or injured animals and those in need of behavioral rehabilitation have a place to go until they are ready to be adopted, animals are saved. The four walls of the shelter, previously identified as a limiting factor, no longer are so. The shelter is more a part of the community. Volunteers work for free and create good will.

5. A Comprehensive Adoption Program: Most people who acquire pets don’t get them from shelters. Getting animals adopted into homes, having them emigrate into the population of pets with homes needs to be a central mission of any shelter. Shelters need to present a clean and inviting environment to the public and to effectively market shelter pets in a variety of different ways, including the internet and social media. Shelters should be open at times when working people and families with children can actually visit them. They should bring the pets into the community with offsite adoptions. Volunteers can help with this. It needs to be done vigorously.

George was rescued from the high-kill Carroll County Animal Shelter.

6. Pet Retention: Sometimes, a little problem-solving can prevent the immigration of pets from the homed population into the shelter population. Blaming people is counterproductive, but helping them solve the problems that lead to pets being surrendered to shelters gets results. Do they need some pet food to get through a difficult financial time? Tips on getting their cat to use the litter box? A referral for training for a rambunctious dog? Shelters need to act like they believe that pets are not disposable and to help people do the right thing wherever possible.

7. Medical and Behavioral Programs: Shelters are obligated to ensure that all animals in their care who are ready for adoption stay that way, and that those who are sick, injured, too young or in need of behavioral rehabilitation get it. A healthy shelter pet population will emigrate into the homed pet population. Failure to have these programs results in an increased and unnecessary death rate.

8. Public Relations/Community Involvement: By keeping the shelter and its programs in the public eye, there are more opportunities for shelter pets to emigrate into the homed pet population by being adopted, more opportunities to reduce the birth rate through low-cost spay-neuter, more opportunities to help people retain pets, thus reducing the immigration rate, and more volunteers recruited and donations obtained for programs that reduce limiting factors and reduce the death rate.

9. Volunteers: Shelter pets can’t live without them. They work at spay-neuter clinics, reducing the birth rate. They bottle feed orphaned puppies and kittens, and care for the sick and injured, reducing the death rate. They provide foster homes for animals, removing the space within a shelter’s four walls as a limiting factor. They take pets to offsite adoptions, increasing the emigration rate. They offer advice and assistance, preventing some animals from ending up at the shelter in the first place, reducing the immigration rate. They create good will and make the shelter a part of the community it serves. Shelters need to treat them like the powerful positive force that they are.

10. Proactive Redemptions: Many pets at shelters are lost. They have homes and should be returned to them. Traditionally the rate of lost pets being returned to their homes by shelters has been very low and many are killed, resulting in a high death rate. Being proactive prevents this unnecessary immigration or at least greatly reduces its duration, freeing up resources for animals who really don’t have homes.

11. A Compassionate Director: The director is the one with both the power and the responsibility to make it all happen, the keystone that holds the whole NKE together. Sadly such directors are not easy to come by, and many shelter directors thwart rather than promote the implementation of the NKE. The bottom line is that the shelter director must reduce the shelter pet death rate so that it includes only those animals who are irremediably sick, injured or truly vicious. That means that 90% or more of the animals entering the shelter pet population leave that population alive. The director makes the shelter into a true safety net for animals. Such a shelter has a positive image and is both an asset to its community and a point of pride. The circle of compassion is extended to those animals without homes, and they can be more efficiently moved into the homed animal population through the shelter. A growing list of communities as diverse as Tompkins County, NY, Reno, NV, Charlottesville, VA and Shelby County, KY has already accomplished this, even as their shelters maintain an open-door policy, accepting any pet in need.

This article originally appeared here.