Within 24 hours of Gov. David Ige announcing the state’s shelter-in-place order, the Hawaii Humane Society had a 250-person waiting list for cat fosters hoping to cope with loneliness, anxiety and boredom from the COVID-19 pandemic.

Cat fosters are up 65% compared to this time last year, said Daniel Roselle, director of community relations for the Hawaii Humane Society.

While a pet cat can ease stress in humans, the animal can take a huge toll on Hawaii’s environment. The latest episode of our podcast “Are We Doomed? And Other Burning Environmental Questions,” has tips on how to protect Hawaii’s environment from cats, even if you don’t own one.

The Hawaii Humane Society is expecting a boom in the feral cat population post-pandemic. During the 2008 financial crisis, pet abandonment was common and Roselle said shelters in the state have already seen people surrendering their pets.

“We’re preparing for a lot of people coming to our pet food banks because on a reduced or cut income they won’t be able to feed their pets,” said Roselle, who noted that the Humane Society gave away over 6,000 pounds of pet food in April.

Roselle said donating food or money to a local shelter or pet food bank can help someone keep their cat, and protect native animals from hungry cats.

The growing feral cat populations in Hawaii are a bigger issue, Roselle said. Most of the Humane Society’s spay and neuter efforts are paused to insure veterinarians can practice social distancing.

“That is probably the most challenging thing for us to accept,” he said. “We know it’ll have an impact later.”

Cats are an invasive species, and pose unique risks to native birds and reptiles in Hawaii that evolved without feline predators. Cats have contributed to the extinction of at least 33 native island species and are the main threat to dozens of endangered birds, mammals and reptiles.

And cats are indirectly killing species that don’t even live on land, like the endangered Hawaiian monk seal.

There are only about 1,400 monk seals in the world, and a parasite from cat poop is the leading cause of death for seals who call the main Hawaiian islands home, Cara Field, medical director for the Marine Mammal Center, said.

“Other marine mammals definitely can catch it,” Field said. “Some whales, dolphins mostly … so this is not just a problem for monk seals.”

A parasite called toxoplasma gondii is found in a lot of cats. Unlike other mammals, cats are rarely sickened by the parasite, but the cat’s digestive tract does provide the perfect environment for the parasite to reproduce.

“At this point, there’s no other animal that we know that can spread it,” Field said.

If a cat is pooping outdoors, thousands of these parasites can make their way into streams, rivers and the ocean — infecting any mammals along the way.

And it’s not just feral cats causing problems. Pet cats that are allowed to roam outdoors also spread toxoplasma gondii and kill endangered wildlife.

A recent study found free-roaming pet cats can impact local ecosystems four to ten times more than a natural predator. Because domesticated cats often stick close to home, their territory is much smaller than a wild predator and therefore the cat has an outsized impact.

“This is not about blaming cats because I love my cats,” Field said. She built her pets an enclosed patio, or “cat-io,” so they could enjoy the fresh air without hurting the environment.

“Building yourself a cat-io would actually be a good project if you’re bored at home,” she said.

“Are We Doomed? And Other Burning Environmental Questions” is funded in part by grants from the Environmental Funders Group of the Hawaii Community Foundation and the Frost Family Foundation.