Feral pigs

Feral European pigs, a late eighteenth century introduction, may be the largest mammalian threat to native forest ecosystems in the Hawaiian Islands. Feral pigs dig up young trees to eat the roots and spread weed seeds. Native plants and crops like sugarcane are attacked. From New Zealand to the Galápagos Islands, feral pigs also have a reputation for digging into burrows to consume seabirds like petrels. Feral pigs also feast on the eggs and young of surface-nesting seabirds like boobies, shags, and albatrosses.

The original pot-bellied pigs introduced from Polynesia into the Hawaiian Islands in the fourth century are smaller, more docile animals and a different genotype than the larger, much more aggressive European pigs. Polynesian pigs are also less inclined to roam and go feral, and are less of a threat to the native ecosystems of the Hawaiian Islands.

Most popular accounts date the arrival of the European pig genotype in the Hawaiian Islands to the arrival of British ships under the command of Captain James Cook in 1778. Apparently the British were disappointed by the small size and tougher texture of the meat of the Polynesian pig, and so

The opossum (Didelphis virginiana) has adapted to life near humans, and has been known to raid hen houses and attics of homes. (Photo by Steve Maslowski/Photo Researchers, Inc. Reproduced by permission.)

introduced the larger, more succulent European pig to the Hawaiian Islands.

In the nineteenth century, the introduction of new species was viewed as a positive and encouraged. Indeed, mid-nineteenth century advertisements exhorted sea captains to import and release their favorite songbirds in the Hawaiian Islands. Even in the mid-1800s, settlers in the Hawaiian Islands noticed forest habitat destruction and native bird losses, and felt that the introduction of their favorite European species would help compensate. Never mind that previous introductions like European pigs and goats were among the culprits destroying the habitat. It was an age when feral European species were welcomed by hunters, albeit opposed by agricultural interests suffering crop damage.

By the early twentieth century European pigs had completely displaced Polynesian pigs in the wild, and an eradication program was started because of feral pig damage to the Hawaiian Islands' native rainforests. By the mid-twentieth century, 170,000 feral pigs were killed. But feral pig popula-

A house mouse (Mus musculus) raids a sack of seeds. (Photo by Stephen Dalton/Photo Researchers, Inc. Reproduced by permission.)

tions were still trampling, uprooting, eating, and otherwise destroying the Hawaiian Islands' native ecosystems.

Though damage by goats, feral pigs, and other grazing mammals seemed obvious to observers, there was little quantitative baseline data against which to measure the ecological impacts. Near Thurston Lava Tube in Hawaii Volcanoes National Park, the National Park Service set up an experiment in which some forest plots were fenced to keep out feral pigs. Compared to unfenced plots where pigs roamed freely, fenced plots had fewer exotic plant species and more native plant species. Fenced plots also had less pig damage, as measured by fewer exposed plant roots and less exposed soil. Not surprisingly, fencing is used as an integrated control measure to keep pigs out of sensitive areas.

The National Park Service has also been following the spread of feral pigs from lower to higher elevations on the Hawaiian island of Maui. Feral pigs were removed from Maui's Kipahulu Valley in the 1980s. Removing the pigs allowed the forest understory to recover and slowed the invasion of exotic plant species, a positive ecological outcome. Nonetheless, there has been opposition to using snares and hunting to remove the pigs. Indeed, one person's invasive mammal pest may have redeeming positive qualities for another person. Hunting groups want the pigs to remain as game, and some indigenous groups oppose eliminating the pigs for cultural reasons.

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