FIVE THINGS ABOUT A CAT FENCE

1 CATS NOT WELCOME

On Hawaii’s Big Island, you are welcome to visit Mauna Loa, the largest volcano in the world. Cats, however, are not — a point now being enforced by a new eight-kilometre fence constructed for the sole purpose of keeping felines away.

2 CATS LIKE BIRDS

Mauna Loa’s lava-covered slopes make for some forbidding landscape, but that hasn’t deterred cats, which have adapted to the Hawaiian islands since arriving on explorers’ ships. So fine, in fact, that the invasive predators are now a threat to the endangered Hawaiian petrel, a seabird that breeds on Mauna Loa.

3 ERGO, A FENCE

To protect the petrels, the National Park Service and other organizations spent three years flying in people and materials to build the barrier, a two-metretall fence topped with a curved section that even the wiliest kitty can’t scale. It’s the longest anti-cat fence in the United States, and it encloses 240 hectares of high terrain.

4 EASY PREY

Hawaiian petrels are seafaring birds that arrive at Mauna Loa, part of Hawaii Volcanoes National Park, to build nests in deep lava crevices in April. In June, females lay just one egg. The egg hatches in August, and the chick does not fly away until November. That leaves seven months for feral cats to scale the slopes and feast on adult or baby petrels.

5 FENCES ELSEWHERE

Hawaii is home to a handful of cat fences, but the leaders are Australia and New Zealand, where cats and other invasive predators have helped wipe out so many species that the governments have declared all-out war on them. One fence in Australia is 42 kilometres long.