There is no centralized organization maintaining an accurate headcount of cats in shelters, so the best numbers we have for the total shelter cat population in the United States are estimates. According to the president and CEO of the Humane Society of the United States, between 6 million and 7 million dogs and cats enter shelters every year. Since 2010, yearly reports have been fairly consistent that of the total, about half (around 3.5 million shelter animals) are cats, and each year, nearly half of that (around 1.7 million) are euthanized. That is a shocking amount of needless and preventable death.

Spay or neuter your cats

None of these numbers so far has touched on the population of feral or homeless cats, of which there might be as many as 30 million to 40 million. Fewer than 2 percent of these cats have been fixed. Beyond all doubt, spaying your female cats and neutering your male cats are two of the most important and responsible things you can do as cat owners. Not only does getting your cats fixed contribute to minimizing shelter populations, but it can also prevent spraying in male cats and reproductive cancers in females.

It’s difficult to tell whether a strange cat is neutered

You might be asking, “Why are we spending all this time talking about spaying, neutering, and shelter population statistics?” Because when you look out the window, you see a male cat lurking outside. Maybe you detect the acrid ammonia stench of that same male cat’s urine. He’s been spraying around your house, apartment complex, or in your neighborhood, and you’re concerned he might attempt sexual congress with your intact female cat.

The fact is, determining whether that stray tom has been fixed can be difficult, if not impossible. We’ll relate all the ways available to you that we have found, but most depend on direct physical contact with what could be a quarrelsome, if not dangerous, stray cat. Honestly, it’s hard enough to tell whether a male cat has been neutered even if he is familiar and friendly. It can take a veterinary examination to know for certain. This is why we’re putting so much emphasis on making sure your own cats, male and female, are spayed and neutered.

How to tell whether a male cat is fixed

If you’ve taken a stray male kitten into your home or recently adopted a male cat, the first thing you should do is arrange a veterinary appointment to make sure he gets a proper checkup and has all necessary vaccinations scheduled. Some clinics will not schedule a neutering operation without knowing the cat is vaccinated, or at least current on his rabies vaccine. Before you take the cat in, there are a few cursory investigations you can make to see whether he is already fixed.

• At a distance
  The sniff test: If the male cat is seeking females, he will spray in the vicinity. Cat urine serves a number of functions beyond simple bladder evacuation including marking territorial boundaries. The pungency of the ammonia-like smell might fade, but even the length of time urine lingers communicates essential information to other cats. Of course, another reason male cats spray is to signal sexual availability to potential mates.
• At close range
  Genital exam: This can be tricky. The neutering procedure involves a small incision in the scrotum, through which the testicles are removed. A cat’s scrotum is located between the penis and the anus, just beneath the tail. A fixed male cat’s scrotum will appear and feel flaccid and empty.
  Ear tattooed or clipped: Some cats are microchipped when they are fixed. The cat’s ear might have a tattoo clearly visible. A veterinarian can access the information on the chip to tell whether the cat has been neutered. Some strays or shelter cats who are fixed while in custody might have their ear clipped or tipped to readily indicate that they have been sterilized.
  Broader head and jawline: An intact male cat develops a wider, fleshier head, which offers useful defensive padding in fights with other male cats for mates.
  Shaved abdomen: Abdominal fur must be removed for the surgery, so a cat that has  very recently undergone an operation will have a noticeably bald lower abdomen. It takes a while for a cat to regrow the fur on a shaved area, but it will return in time.
• Behavioral tells:
  Aggressive behaviors become pronounced — especially around other cats of the same sex — when a male cat reaches sexual maturity; this includes loud vocalizations and increased efforts to escape the confines of the home. As above, check vertical surfaces for strong-smelling urine, which male cats use to announce their readiness for sexual activity.

All these methods can be unreliable to the unpracticed amateur. A tattoo or clipped ear might be your clearest and most obvious indicators that the male cat prowling about your residence cannot get your intact female cat pregnant. As for the genital exam, many intact male cats might have undescended testicles, so even a direct and close-up genital examination can foster a false sense of security. The third approach, looking for a shaved spot around the site of the neutering surgery, is the least effective, because the cat’s fur may have long since grown back and resumed its wonted volume.

When to neuter a male cat: eight and two

Contemporary veterinary science has determined that eight and two are the optimal numbers when it comes to spaying or neutering kittens. Once a kitten is eight weeks old and weighs a full two pounds, males and females are sufficiently mature to endure and recover from a sterilization procedure. If you take in an adult stray or adopt a shelter cat, make sure he gets a veterinary checkup to get a proper medical evaluation of whether he’s been fixed. If the cat is not yet fixed, arrange for any necessary vaccinations and schedule a neuter surgery at the earliest opportunity.

About the author: Melvin Peña trained as a scholar and teacher of 18th-century British literature before turning his research and writing skills to puppies and kittens. He enjoys making art, hiking, and concert-going, as well as dazzling crowds with operatic karaoke performances. He has a one-year-old female Bluetick Coonhound mix named Idris, and his online life is conveniently encapsulated here.