When most people envision Hawaii, images of playful spinner dolphins, turtles and colorful honeycreepers are likely to be conjured up. The aesthetic, cultural, spiritual, economic and ecological services that Hawaii’s wildlife provides is invaluable, and a crucial part of what makes these islands unique.

However, native bird populations are significantly declining. According to Ke Ola Magazine, of the original 142 bird species that found refuge in Hawaii, 95 are now extinct. Of those remaining, 33 are listed under the U.S. Endangered Species Act. Introduced predators such as feral cats are one of the drivers of the decline in native bird populations. Predator-proof fenced sanctuaries need to be utilized more intensively to protect endangered Hawaiian birds.

The Hawaiian islands have seen the same story repeated throughout history; invasive species brought overseas cause widespread ecological disruption to native flora and fauna, and feral cats are no exception.

Like feral hogs and coqui frogs, cats made Hawaii’s list for the most impactful invasive species. Feral cats are the dominant predator of many native bird species, both in coastal and forest regions on the main eight islands.

In one week of 2019, feral cats and dogs killed 150 nesting wedge-tailed shearwater birds on the coast of Kauai. Hawaii’s Department of Land and Natural Resources officials report that these large predation events happen multiple times a year, and wedge-tailed shearwater populations cannot withstand such high levels of predation.

Along with preying on native bird species, feral cats spread the parasite Toxoplasma gondii through their feces, resulting in infections of native birds, marine mammals, and terrestrial mammals, including humans. According to the Hawaii Invasive Species Council, the species is a principal threat to 8% of critically endangered birds, mammals and reptiles. By utilizing predator-proof fences, the state would be able to improve the health of endangered bird populations, as well as the health and safety of humans and other wildlife.

Although feral cats have been removed with live traps since 1998, the overall population is still growing, proving these methods to be ultimately ineffective. Some community members are advocates for the trap-neuter-release option, but this has been proven to be the least effective and most costly option in time and resources. Lethal traps and poisoning receive backlash from community members and are simply not sustainable economically.

Fenced predator-proof sanctuaries in New Zealand and Oahu have proven to be successful and more cost-effective over the long term. A study conducted in New Zealand found that predator-proof fences were positively correlated with native bird densities, foraging rates and native plant seed dispersal. Predator-proof sanctuaries need to be implemented more intensively and widespread throughout the islands.

By educating the public about invasive feral cats and establishing fenced sanctuaries throughout the islands, the native Hawaiian bird populations will stand a much better chance at recovery. Preserving native Hawaiian bird species is essential to conserving the rich diversity of Hawaii’s rainforests and coastal ecosystems for future generations.

Carina Kusaka, of Wahiawa, is pursuing her bachelor’s degree in fish, wildlife and conservation biology at Colorado State University.