Behind a Bronx apartment building, two elusive trespassers were about to be taken down in a stakeout. The bait: a stinky pile of tuna fish.

The pair — known as Blackie and Kitty — warily circled a wood-and-net trap propped up with a stick. Kitty, the younger and less worldly one, finally darted in for a lick. The trap slammed down with Kitty inside. Blackie skittered away to glare from behind a tree.

“Most of the time it’s a waiting game,” explained their trapper, Bernadette Ferrara, 57.

Ms. Ferrara is part of a growing network of trappers, feeders and rescuers who say they have no choice but to step up to care for lost and unwanted animals in the Bronx — a borough with city shelters for the homeless, but not one for animals. Their grass-roots effort comes amid renewed concern among some elected officials and animal welfare groups that New York City’s animal control programs and services are woefully inadequate.

“There is such overcrowding in the Manhattan and Brooklyn shelters that the animals are often stacked in cages and left in overflow hallways,” said Scott M. Stringer, the Manhattan borough president, who is preparing a report on the shelters. “They’re treated like old file cabinets.”