“When people ask me why I do it, I tell them, ‘Because you don’t do it,’ ” said Ms. Massaro, whose group, the Spay Neuter Intervention Project, or SNIP, arranges for spaying, neutering and vaccinations.

Ms. Massaro, a retired word processor for a Manhattan law firm, said she supported the group largely with her own pension checks. Finding the animals better homes sometimes requires some creativity, as with the scrawny black cat she pulled from the streets of Brownsville and installed as the mascot of a Liberty Avenue social club that was well known as a mob hangout.

Driven by a reporter on a recent weekday, Ms. Massaro started by picking up a shopping cart full of food at Pet Supplies Plus in Maspeth, the Queens neighborhood where she lives. After feeding Gina, she spied a scraggly cat across from a bodega and then heard more meowing.

“Somebody’s crying,” she exclaimed, sounding like a protective mother, and she followed the sound to the basement entrance of a residence. She opened the sidewalk doors and pulled out a second skinny cat by the scruff of its neck. A tenant came out and under interrogation by Ms. Massaro, insisted that he had no idea how the cat wound up trapped in the basement. “He’s lying,” she said flatly, after telling him she would be back to have the cats neutered.

At a homeless shelter on Eastern Parkway, she bristled when a worker told her that he “got rid of” feral cats on the property.

“The only thing I get rid of is my garbage,” she snapped.

Ms. Massaro grew up on the Lower East Side. Her twin sister died at birth, and she became the oldest of four girls.

“When I was a teenager, my mother threw my father out on the street, and I would see him on my way to school,” she recalled. She worked to get him social services and housing in a nearby men’s shelter.