Whether you're dealing with two cats or twenty, the goal is to get 100 percent of the colony spayed and neutered. Catching and fixing all the cats at the same time ("mass trapping") is the fastest way to accomplish this, but if you need to, you can move at a slower pace using similar techniques. The basics of mass trapping are described here.
ADVANTAGES OF MASS TRAPPING
Quickly get the colony under control - In a matter of days, what may have been a bad situation with upset neighbors is dramatically improved. Yowling, foul odors, mating and fighting activity - all are eliminated or greatly reduced practically overnight. Plus no more kittens!
Less time and effort overall - Mass trapping is more efficient than a one-at-a-time approach. Securing traps, finding a holding space, arranging transportation and making spay/neuter appointments only need to be done once instead of repeatedly over a period of weeks or months.
It's easier to catch all the cats - Trapping one cat at a time is relatively easy in the beginning when all the colony cats are candidates for capture, but when you get down to the last ones, you have to pick them out from the crowd which can be tricky. With mass trapping, the last cats are the only ones out in the territory and with each day of the trapping, they're getting hungrier and more likely to go in.
The logistics - Well before the trapping begins, a number of pieces must be in place. You need to find a holding space that is warm, dry, secure and large enough to house the number of cats you plan to trap. Spay/neuter appointments must be scheduled, traps borrowed or purchased and transportation arranged. Identifying emergency veterinary care, in case it's needed post-surgery, is also highly recommended.
Establish a feeding pattern - Feral cats are much easier to trap when they've been trained to eat in a predictable pattern. If you know where and when the cats show up, then you also know the best time and place to set out your traps. To train them, put out their meals in the same location at as consistent a time as you can manage. Try to pick at time that will work best for the trapping, such as late morning as opposed to 2 am. The cats will quickly learn to be there, waiting for you.
Withhold food - Feral cats are naturally wary of entering the narrow confines of a box trap. Before most will go in, they need to be hungry enough to overcome their fear. It is critical to withhold food the day before the trapping so that they'll be very hungry the next day. Check the site periodically to make sure no one stops by and leaves out a bowl of kibble. Continue to provide fresh water daily.