Regardless of the exact mechanism, having a large number of feral cats around means trouble for more than just animal shelters. Cats are apex predators that can wreak havoc on local biodiversity. Research shows that outdoor cats on islands have already caused or contributed to the extinction of an estimated 33 species. Wild cats pose an outsized threat to birds, which make up half their diet. On Hawaiʻi, known as the bird extinction capital of the world, cats are the most devastating predators of wildlife. "We know that cats are an invasive, environmental threat," said Lepczyk, who has published papers proposing management policies for outdoor cats.

Scientists, conservationists, and cat advocates all agree unchecked outdoor cat populations are a problem, but they remain deeply divided on solutions. While some conservationists propose the targeted killing of cats, known as culling, cat populations have been observed to bounce back quickly, and a single female cat and her offspring can produce at least 100 descendants, if not thousands, in just seven years. 

Although sterilization protocols such as "trap, neuter, and release" are favored by many cat rescue organizations, Lepczyk said it's almost impossible to do it effectively, in part because of how freely the animals roam and how quickly they procreate. Without homes or sanctuaries after sterilization, returning cats outside means they may have a low quality of life, spread disease, and continue to harm wildlife. "No matter what technique you use, if you don't stop the flow of new cats into the landscape, it's not going to matter," said Lepczyk. 

Rescue shelters, already under strain from resource and veterinary shortages, are scrambling to confront their new reality. While some release materials to help the community identify when outdoor kittens need intervention, others focus on recruiting for foster volunteer programs, which become essential for kittens that need around-the-clock-care.

"As the population continues to explode, how do we address all these little lives that need our help?" Dunn said. "We're giving this everything we have."