On a nondescript block in east Ferndale slammed with foreclosures and vacancies, a new breed of squatters is slowly taking over.

A colony of dozens of homeless cats are living, breeding and dying among the houses on this street. At one house, the smell of urine fills the air along the foundation.

By one estimate, there are about 657,000 feral cats in metro Detroit — that's 16 cats for every seat at Comerica Park. The cat population strains animal control and animal welfare groups, which say they have limited money and space.

Free-roaming cats often harbor illnesses that spread between cats and sometimes, to humans, said Dr. Steve Halstead, state veterinarian.

Just one example: Pregnant women are advised against cleaning litter boxes for fear of the parasite that causes fetus- endangering toxoplasmosis; gardening in cat-trafficked yards carries a similar risk.

Southfield has agreed to be the pilot community for a $100,000 county program to catch, sterilize and release feral cats and a Warren animal welfare group is teaching people how to literally herd cats.

"You can't just adopt your way out of the situation," said Amber Sitko, president of All About Animals Rescue in Warren.

More animal welfare groups are promoting trap-neuter-release programs as a surefire way to decrease the population of feral or free-roaming cats in the Detroit area, but wildlife groups say the programs don't alleviate all of the problems.

By one calculation cited by the Petsmart Charities, there are approximately 657,000 homeless cats in the area. The Humane Society of the United States estimates the nation's free-roaming cat population at 50 million, while another study published by Best Friends Animal Society estimates 87 million feral cats nationwide — 22 cats for every square mile of land and water in the U.S.

Linda Reider, director of animal welfare for the Michigan Humane Society said fixed cats returned to their colonies fight less, live longer and limit the population in a colony. Killing cats, she said, just leaves a hole in a colony another cat will fill.

But opponents of trap-neuter-release programs say even if the cats can't reproduce, they can still kill wildlife and harbor cross-species infectious diseases such as rabies.

The Wildlife Society, based in Bethesda, Md., said free-roaming cats kill lizards and birds and that colonies do not self-limit.

The organization instead supports the adoption of indoor-only cats and euthanasia of unadoptable cats and cites a University of Georgia study that says at least 1 billion birds die in cat attacks each year.

In Ferndale, Shirley Lappin has cared for dozens of cats that roam her street, but after five years, she's moving. One of her last acts is to trap as many of the cats as she can, and get them fixed on her dime.

"If I get them neutered, they'll be easier to adopt," Lappin said one afternoon, holding one of a litter of kittens in her hands. Two other kittens wrestled behind her. Several older cats slept wherever they could find space. Having learned about trap-neuter-release from All About Animals in Warren, she borrowed the group's traps and agreed to bring in as many as she could fit in her car to be fixed.

Shelter President Amber Sitko said the organization fixes hundreds of cats per month, and trains people how to trap. It costs $25 to spay or neuter each cat.

On June 12, the organization will hold another training session.

Local animal control officials paint a grim picture of feral cats' futures. The few animal control departments that can handle nuisance calls will help residents trap cats, or take trapped cats. But animal control officers said there aren't many shelters or rescue organizations that can manage them.

The Michigan Humane Society reported that it took in 13,725 kittens and adult cats, and seven of every 10 were killed, according to the 2010 Animal Shelter Activity Survey released by the Michigan Department of Agriculture and Rural Development.

The Humane Society of Macomb in Utica reported about an 85 percent kill rate for the 1,780 cats it took in last year. The Allen Park Animal Shelter euthanized 66 percent of the 1,002 cats it took in last year. Other facilities posted a wide range of euthanasia rates, or transferred their felines to unspecified facilities.

"It's not the shelters' fault," said Warren Animal Control Officer Timothy Herig. "People are not being responsible. The whole city has just as many cats as squirrels."

For those in communities where animal control is overwhelmed by cats, or simply cannot take those calls, people pay out of pocket to have them removed.