Stray cats are those that were owned by a person but then became lost or were abandoned. Feral cats are domesticated cats that were never around people and are wild.
Researchers in Israel recently studied the most effective way to keep their population numbers in check.
Communities have often controlled free-roaming cat populations with a program called TNR or trap, neuter, return/release. TNR involves trapping roaming cats, spaying and neutering them, and then returning them to their territory. They are typically also vaccinated and “ear-tipped” for identification. That’s when a small part of the top of the ear is removed during surgery. It’s the universally recognized way to tell if a feral cat has been neutered or spayed.
Pros and Cons of TNR
TNR can be a controversial program. It’s considered more humane than culling, but released cats are still a threat to the wildlife population.
It’s also expensive and laborious, Klement says, pointing out that the program is only effective if at least 70% of cats in an area are spayed or neutered.
“As we showed, things are complicated by the fact that intact cats can migrate between non-neutered areas to the neutered ones and therefore this method should be performed in contiguous areas which are secluded from un-neutered areas,” he says. “Another pitfall is the occurrence of potential compensation mechanisms such as increase in kitten survival.”
Dozen Years of Research
For their study, researchers followed cats for a total of a dozen years so they could analyze the long-term effects of each population-control method. They focused on free-roaming cats in Rishon LeZion, one city in Israel.
They tested three different methods, each for a four-year period. In the first, they did not intervene with the cat population at all for four years. In the second, they organized a program where they altered cats in half of the city’s 50 zones, while the other zones were a control group with no intervention. In the third four-year period, they applied TNR to the city’s entire roaming cat population.
“It was very critical to follow the population for such a long period because even theoretically it takes time in order for TNR to reduce cat numbers,” Klement says.
In many previous studies, the follow-up period was two short (two years or less), he says. Other longer studies didn’t include control groups or control periods.
“Our study is unique as it is controlled twice in time and in space. Just to understand the scale of this study, previous studies included a maximum of four areas of follow up (and those were short-termed), while in the current study we followed 50 regions, half of which were extensively neutered and half of which were not neutered or in which neutering rates were very low,” Klement says.
Researchers kept track of the cat populations by performing professional counts, but they also analyzed citizen reports to the city call center about free-roaming cat births and deaths.
They found that spaying and neutering cats in only half of the city zones didn’t end up reducing the cat population. That was likely because unneutered cats made their way into the areas where other felines had been fixed.
In the final testing period, they found a 7% annual drop in the cat population. But it was accompanied by an increase in the number of kittens and longevity, likely because there was less competition with neutered, less aggressive cats.