The North Shore got some help Monday from a mobile clinic tackling an overpopulation of feral cats by providing residents a cheap way to get their pets spayed or neutered.

Poi Dogs and Popoki stationed its Big Fix Mobile Clinic at the Kahuku Medical Center, where a veterinarian performed the sterilization procedures at a reduced rate of $5 per cat. The event was sponsored by the Na Pua Makani wind energy facility.

Typically, it costs $50 to spay a female and $40 to neuter a male, clinic officials said. Residents who brought in a feral cat were not charged.

Hospital officials said feral cats have taken up home on the grounds, becoming a nuisance to staff and patients. By midafternoon more than two dozen cats had been trapped to be sterilized.

Cats sterilized at the mobile clinic were microchipped.

Female cats were tattooed with a small green line on their stomach, and male cats were tattooed near their groin. A tiny notch also was made on the left ear for male feral cats and right ear for female feral cats to indicate that they have been fixed.

Inside the air-conditioned mobile clinic, Dr. Eileen Lau, with the Animal House Veterinary Center in Ewa Beach, spent her day off conducting procedures on a mix of feral and pet cats, 54 in all.

In a news release, Alicia Maluafiti, executive director of Poi Dogs and Popoki, said in Hawaii’s warm climate a female cat can produce three litters per year in her 10-year breeding cycle. “With eight surviving kittens per litter and few natural predators to keep the population in check, one unsterilized female cat and her offspring can give birth to more than 400,000 kittens in those 10 years.”

A stream of area residents drove to the mobile clinic.

Hauula resident Tammy Nichols, who tends to feral cats in her neighborhood, dropped off several cats, a couple owned by a friend.

“I think I’m making a difference,” said Nichols of her efforts to reduce the feral cat population.