Early on a muggy Monday morning, Sarah Dykstra stood on a sidewalk in West Philadelphia’s Mill Creek neighborhood and popped open a can of oil-packed sardines. Diving in with her hands, she scooped out two tiny fish and placed them on a sheet of newspaper that concealed a several-foot-long trap. Slowly, the pungent smell permeated the summer air.

Within seconds, three hungry stray cats emerged from a nearby alley. Three more followed on their furry heels, scouting out the scene. One nuzzled the trap’s metal grates. He would be the first to venture inside.

“My husband is always upset because my car stinks,” said Dykstra, a Trap Neuter Release (TNR) coordinator with Project MEOW. She spends at least 10 hours a week trapping. “If the cats are really hungry, they’ll go in for anything, but sardines really do the trick.”

There are around 400,000 free-roaming cats in the region, according to ACCT Philly, the city’s official animal shelter and control provider. And TNR — a humane practice in which outdoor cats are trapped, spayed or neutered, then released back to their original location — is one of city residents’ most powerful strategies in keeping that population in check. It’s been shown to be effective in decreasing the number of strays.

One cat can get pregnant three times a year, and female kittens can start reproducing as early as six months old. Removing mating from the equation means fewer kittens being born on the street. That, in turn, means fewer cats coming into shelters, which directly impacts euthanasia rates.

But TNR has more immediate effects, too. “[Mating puts] a lot of stress on the cats,” said Kelsey Lauder, communications director at Stray Cat Relief Fund, a volunteer-run nonprofit that coordinates trappings around South Philadelphia. When they’re already prowling for food, the search for a mate only adds to stray cats’ hardships.

“Fixed cats are happier, healthier, and a lot less of a nuisance,” said Alley Cagnazzi, community cat coordinator at ACCT. “They tend not to roam around as much, or fight and howl, and wake people up in the middle of the night. They also aren’t as likely to spray all over your house.”

For the most part, local rescue organizations and volunteers like Dykstra spearhead TNR efforts. But with hundreds of thousands of strays, they can always use more help. Here’s what to know about TNR and how to get involved:

Trap: Where to get one and how they work

“If you can open a soda can, you can set a trap,” said Aine Doley, founder of Catadelphia, one of the city’s largest TNR organizations. It’s one of several organizations in the area that will lend you a trap for free and teach you how to use it. It keeps a 150-trap inventory in its Germantown headquarters. (Call or reserve online.)

There are two main types: traditional humane cat traps and drop traps. The first is the most common and looks like an oversize cat carrier completely composed of metal grates. The bottom gets layered with newspaper to make it more comfortable and to absorb waste. Food is placed at the back as bait. At the center of the trap is a trip plate, which triggers the entrance door to close once the cat walks over it. Sometimes a few pieces of kibble are placed at the opening, as well, to lure the cat inside.

Drop traps — propped-up cages that are manually triggered shut — are primarily used for catching shy or savvy cats. Animal rescue staff often assist individuals deploying drop traps.

"Trapping can actually become quite addicting, because you’re doing something that’s making a direct impact,” said Cagnazzi.

While Catadelphia currently houses the most extensive local trap library, ACCT also lends out free traps, as do organizations including Stray Cat Relief Fund, Project MEOW, Forgotten Cats, The Spayed Clinic ($50 returnable deposit), and NE Philly AdvoCATS. Demos are generally given at the time of pickup, but detailed instructions are available online, as well, from national organizations like Alley Cat Allies.

Prior to setting traps, introduce yourself to the surrounding community, especially if you plan to expand your efforts beyond your own backyard. If you trap a cat with an ear that’s missing the very tip, it indicates the cat has already been spayed or neutered and should be released.

“You want to have a handle on the situation, so that you’re not taking people’s pets that are already fixed or stirring up controversy by trapping on property where you haven’t gotten permission,” Dykstra said.

Traps work best placed against a wall or fence, so they blend more closely with their surroundings. Dykstra recommends draping a towel over the top to make the trap seem like a hiding space.

“Unless it’s in a place where you can keep an eye on it, don’t leave the trap for very long, because the cat will be exposed to weather and predators,” Dykstra added, noting that really hot temperatures can cause death. “I recently trapped seven cats in 20 minutes. If they’re hungry, it often won’t take long.”

Neuter (or spay): Where to go next and what to consider

After you’ve trapped a cat, you can head to an organization like PAWS, Forgotten Cats, or the Spayed Club — all of which take in and fix trapped cats. Prices vary, but fees are kept as low as possible; PAWS, for instance, charges $25. ACCT, in North Philly, is the only center within city limits that performs the surgery free of charge.

Strays get their ears tipped, to signal they’ve been fixed. Many organizations will also give them vaccinations for rabies and distemper (FVRCP), a dewormer, and a flea treatment. ACCT will treat illnesses and injuries, too, ranging from upper respiratory infections to leg amputations.

“It’s great for the trapper who probably doesn’t have a million dollars to take care of those things, and for the cat, who likely won’t see another vet in their lifetime,” Cagnazzi said.

ACCT houses the cats post-surgery for the necessary 24-hour recovery period and will release the cats back to their original location, unless you opt to retrieve and release yourself. Elsewhere, you may be on the hook to shelter the cat immediately after surgery.

If you need backup transporting strays, partner up. Catadelphia’s PHL Community Cats Facebook page has more than 4,500 members who frequently collaborate on various parts of the TNR process. Some organizations, like Project MEOW, also help volunteers connect and team up.

Release: Back to the street

After the cats have had a minimum of 24 hours to recover from their surgery, they’re ready to be released near where they were trapped. Though it may seem harsh, for some cats, life outside is all they know.

“Most of these cats have been on the streets most of their lives and will never be happy inside," Dykstra said, adding that this type of cat will likely not make an owner happy either. “They’ll live happier lives outside, even if it’s more of a challenge.”

Plus, she added, “if animal control were to take in every cat and then try to find them homes, cats would be euthanized en masse, because there’s nowhere to put them. This is a chance for animals to keep living.”

TNR in itself may seem like a stressful process for cats, but rescue staffers universally emphasize that the cats end up happier in the long run. In the Mill Creek neighborhood, where Dykstra spends time trapping, you’ll find dozens of fixed, healthy-looking strays lounging like any house cat would — sprawled out in a dirt alley instead of a couch cushion.

“Look, it’s Mamacita,” said Shireen Patterson, pointing out a gray-brown tabby as Dykstra set a second trap.

Patterson, a neighborhood cat feeder, works frequently with TNR volunteers. She keeps track of the new cats that show up to her feeding station, lovingly labeled “Four Paws Diner -- open 24 hr.” (Patterson actually opens it daily at 9 a.m.) Since January, 23 cats that came to the diner have undergone TNR, Mamacita among them.

“She’s probably given birth to about five litters, but she’ll never be a mamacita again,” said Patterson with a proud smile and can of wet food in her hands.