Feral pets add to interlopers’ toll

Dogs and cats that prey on native birds join the widening list of ecological villains

Pillaging native forests, screeching through the night in suburban neighborhoods and rooting around in rural taro patches, wild animals of Hawaii's ancient past and globalized present abound across the islands.

Stealthy and sometimes nearly invisible, unwelcome species such as hybrid Polynesian pigs and a newly discovered gall wasp have eluded eradication efforts and taken hold in an ecosystem that was once home to only one terrestrial mammal, an insectivorous bat.

Some non-native animals, like the vocally endowed coqui frog from Puerto Rico, arrived by accident.

Others -- like the Big Island's wild horses and cattle, Molokai's resident goats and Honolulu's legions of feral felines roaming the Iolani Palace grounds -- were released deliberately for hunting or broke free from the two-legged residents who brought them.

In the island's warm, moist, Petri dish-like environment, some of these interlopers -- known as invasive species -- have flourished and helped push out the species that evolved here.

Partly as a result of island interlopers, Hawaii has more than 300 endangered and threatened plant and animal species accounting today for about a quarter of the nation's protected species.

Humans have strengthened their defenses against the animals, spraying lethal citric acid to kill coqui frogs and setting out traps for pigs in suburban Oahu. And one Big Island taro farmer publicly acknowledged earlier this year shooting dead several wild horses that had damaged his crops.

Still, despite the annoyances and ecological upheaval these introduced animals and plants have caused here, not everyone feels they all need to be wiped out.

"I think semantics plays a big role in this. The term 'invasive species' makes one think that the hordes are at our gates and threatening to destroy life as we know it, when actually the animals who are considered invasive for the most part had no say in coming to Hawaii," said Cathy Goeggel, Animal Rights Hawaii director.

Goeggel advocates fencing out and relocating the problem animals, such as rooting pigs.

Some sympathetic residents even help the survival of non-native animals, setting out food for cats, including those known to prey upon colonies of native birds on Maui.

Hawaii wildlife officials, however, made their own stance on the feral pet issue clear earlier this month.

State-hired hunters shot and killed four dogs on Nov. 6 believed to have slain at least 113 fledgling wedge-tailed shearwaters inside an Oahu nature reserve.

"Pets that are abandoned or left to run loose in a Hawaiian ecosystem become predators with catastrophic results," said Peter Young, director of the Department of Land and Natural Resources, following the shootings.

There are about 9,975 endemic species currently living in the islands. Another 1,100 endemic species once lived here but disappeared as invasive species showed up, said Earl Campbell, who heads the Invasive Species Division of the U.S. Fish and Wildlife Service's regional office in Honolulu.

Of the approximately 5,000 alien species in Hawaii, only about 300 to 500 have gone on to wreak significant damage, and some, including agricultural plants, are even beneficial, he said.

Still, the problem of invasive species looms much larger in isolated island environments than on the mainland.

"If you look at factors that cause problems for species, invasives are important in many places. But here it is the primary reason right now that things are declining," Campbell said.

That is in part because the islands' native inhabitants have evolved without the defenses needed to fend off the aggressive attackers and competitors they now face, he said.

Mint in Hawaii is not minty. Nettles do not have stings. And unlike their continental cousins, Hawaii's native variety of raspberry does not have prickles.

That means native raspberry plants are not tough enough to withstand the ground foraging of non-native animals such as pigs -- which opens the door for foreign varieties of raspberries well equipped to stand up against such adversaries.

"It's the mix of everything that builds and exacerbates a problem even further," Campbell said.

At the center of it all are people who need to recognize their mistakes and think more about how to make things better, said Christy Martin, spokeswoman for the Coordinating Group on Alien Pest Species, a partnership that brings together a long list of federal, state and private agencies including the Nature Conservancy, National Park Service and the Hawaii Visitors and Convention Bureau.