Why is this cat missing some of its ear?
From time to time, you may see a cat missing the tip of one ear. This doesn't mean the cat was in a fight or got injured - it means the cat has been spayed or neutered.
The ear tip makes it possible to see that a cat has already been taken care of, and when cats arrive to a veterinary clinic it helps avoid putting him or her under anesthesia to conduct surgery, looking for something that has already been removed.
Ear tipping is a simple procedure that occurs under anesthesia.
The universal standard is to take the tip off of the left ear. Sometimes you may see a cat that is missing the tip of the right ear, this is usually a mistake. There are friendly cats in shelters, waiting for homes, with an ear tip. This means someone found the cat and brought it to a veterinarian to be sterilized, thinking it would go back outside. If the cat is friendly and used to humans they're often made available for adoption instead.
Why an ear-tip?
The ear tip is safe and effective, and it can be seen from a distance.
All cats, even community cats, should be microchipped, but the microchip isn't visible. There's no way to look at the cat from a distance and determine if it is microchipped - the cat must be trapped and brought to a shelter or clinic that can read the chip with special equipment.
A tattoo can be a good mark to signal a pet is sterilized - but this doesn't work well for free roaming cats, since you can't see the tattoo from a distance. There's a good chance the cat has to be trapped and anesthetized before anyone sees the tattoo.
Collars aren't safe for community cats, for many reasons. The collar can get caught on something and trap or injure the cat. It can fall off, or if the cat's weight changes the collar will become too tight or too loose. Eartags can cause infection, fall off, or tear the cat's ear.