What is Eartipping?
Have you ever seen a cat outside that appears to be missing a piece of its ear? If it is in a location managed by a TNR team, it is very likely that cat is eartipped!
Eartipping is the universal sign that a feral cat has been sterilized (spayed or neutered) and vaccinated, and the practice is employed by most TNR organizations.
Being trapped is stressful for feral cats, even when we try our hardest to make it as easy a process as possible. When a cat is eartipped, it provides a visible marker that the eartipped cat doesn't need to be trapped again. If an eartipped cat is captured, they are immediately released.
This is particularly important for female cats, as it can be extremely difficult to tell if she was already fixed without going under surgery again. While missing the tip of her ear may not be pretty, she definitely would prefer that to the risk of undergoing invasive surgery a second time unecessarily!
Even short of unecessary surgery, eartipping cats as they are treated in the community allows TNR groups to see where their work is no longer necessary. If you don't see any cats without tipped ears, that means you can put the traps away. If time goes by and you see another cat with both ears in-tact, it means the cat was either dumped or moved in and needs to be captured.
Does it Hurt the Cat?
No more than a standard surgery. Eartipping is performed by a licensed veterinarian while the cat is already sedated for their spay/neuter surgery, so they cannot feel the cut. As the cat recovers from their sterilization surgery, the edge of their ear also heals and does not have any lasting effect on the cat. Enough ear is not trimmed to damage the cat's hearing, and risk of infection is even lower than the risk that comes with sterilization.
What Do I Do If I See an Eartipped Cat?
Leave them alone! They are doing their job to control the stray cat population in your area simply by being there. If one is friendly to people, you aren't forbidden to take them in -- but it is better to have a bunch of eartipped cats in your area than ones that aren't.
You can support eartipped cats at work by providing food or outdoor shelters. Keeping TNRed cats healthy and fed keeps them in the area, which prevents new, unfixed cats from moving in and breeding.
Moving, starving, killing, or otherwise harming a feral cat (especially an eartipped one!) will NOT fix your feral cat problem. As soon as the first is gone, a new cat will find the "abandoned" territory, and the issue will continue, as described by the Vacuum Effect. By performing TNR and eartipping those cats, kittens and communicable diseases prevented by vaccinations can be avoided, and "annoying" feral cat problems (such as yowling and fighting) can be reduced or stopped altogether.