Hawaii does not have native wild cat species. The cats found roaming outside human homes in Hawaii are feral cats, which are descendants of domesticated cats.
Hawaii’s Unique Ecosystem
Hawaii’s geographic isolation has resulted in a distinctive ecosystem. Native species evolved without large terrestrial predators. Many native Hawaiian birds are ground-nesting or flightless, lacking natural defenses against mammalian threats. This made the islands vulnerable to introduced species. Only two mammals are native to Hawaii: the Hawaiian hoary bat and the Hawaiian monk seal.
Feral Cats and Their Origin
Domestic cats, known as “popoki,” first arrived in Hawaii with European explorers and colonists, likely aboard sailing ships in the early 1800s. They were initially brought to control rodent populations on ships. Many of these introduced cats eventually became feral, living without human supervision. Feral cats are distinct from stray cats; they are either born in the wild or have lived independently for an extended period, losing their socialization with humans.
Feral cat populations have established themselves across all eight main Hawaiian Islands, thriving in diverse habitats. Estimates suggest a substantial population, with over 300,000 feral cats on Oahu alone, and around 2 million free-roaming cats across the islands. Their widespread presence is due to rapid reproductive rates and the absence of natural predators.
Threat to Native Species
Feral cats pose a significant threat to Hawaii’s vulnerable native wildlife through direct predation and disease transmission. Their hunting instincts mean even well-fed cats will prey on native species, which evolved without defenses against such predators. This includes ground-nesting birds and seabirds, such as the Hawaiian petrel, Newell’s shearwater, Hawaiian goose (nēnē), Hawaiian coot, Hawaiian moorhen, and Hawaiian stilt. For example, a single feral cat on Kauaʻi killed three pairs of breeding Hawaiian common gallinules, destroying their nests and hatchlings.
Beyond direct predation, feral cats are carriers of Toxoplasma gondii, a parasite causing toxoplasmosis. Cats are the only known animals where this parasite reproduces and sheds oocysts through their feces. These oocysts can contaminate terrestrial environments and wash into marine ecosystems, threatening land and sea animals. Toxoplasmosis has been linked to severe illness and death in endangered Hawaiian monk seals, with at least 11 known fatalities. The parasite can also infect and kill native birds like the ‘alala (Hawaiian crow) and nēnē, as well as Hawaiian spinner dolphins.
Conservation Strategies
Various strategies are employed to manage feral cat populations and protect native species. Trap-Neuter-Return (TNR) programs involve trapping, sterilizing, vaccinating, and returning feral cats to their original location. Proponents highlight TNR as a humane approach to reduce free-roaming cat populations by preventing further reproduction. However, some conservationists argue that TNR is often ineffective at reducing overall cat numbers or mitigating their ongoing impact on wildlife, as even sterilized cats can continue to hunt and spread disease.
Managed cat colonies, where caregivers provide food and monitor cat health, represent a form of TNR. While these efforts aim to control population growth, they can still concentrate cat populations in areas affecting native species. In sensitive conservation areas, more direct measures are implemented, such as humane removal of cats and exclusion fencing. Predator-proof fences, some extending for miles, are designed with features like curved tops and buried skirts to prevent cats from climbing or digging under, protecting critical habitats for ground-nesting birds like Hawaiian petrels and nēnē. These diverse approaches reflect the complex balance between animal welfare and the urgent need to protect Hawaii’s unique and vulnerable ecosystems.