"A cat's cycle is based on day length, and day length isn't changing," said Christine Petersen, assistant professor at Iowa State University's College of Veterinary Medicine. "Temperature's going up a little, but the sexual cycle of the cat isn't based on temperature."

Even if rising temperatures are not directly influencing cats' heat cycles, they can play a role in other ways. Some experts believe, for instance, that milder weather increases kitten survival rates.

And Levy offered another theory — that warming could hasten the onset of puberty in cats, as it does in some other species, creating a larger pool of fertile cats each breeding season.

Yet another explanation could be a "food chain effect," in which warm weather may help more rats and mice survive, providing feral and stray cats with more prey and allowing their numbers to thrive, said Gail Buchwald, vice president of the American Society for the Prevention of Cruelty to Animals Adoption Center in New York.

Whatever the cause, the cat population crisis is hitting animal shelters hard, and in many cases, may result in higher euthanasia rates.

The Humane Society of the United States estimates that half of the 6 million to 8 million dogs and cats that enter U.S. shelters every year are euthanized.

"There just is not enough space, and there just aren't enough homes for all the cats and kittens being born right now," Otis said.

Theoretically, one cat that mates three times a year — cat pregnancies last 63 days and produce four to six kittens — and her offspring could produce 420,000 kittens over seven years, according to the Humane Society of the U.S.

Experts agree that the most critical factor in decreasing the cat population is sterilization through spaying or neutering.

Many veterinary clinics and animal shelters offer discount spay and neuter rates for pet owners, and many also operate programs that trap, neuter and release feral cats.

"We were part of the problem," Buchwald said. "We need to be part of the solution."