Pig wallow found in The Nature Conservancy's Waikamoi Preserve
Grazing wild cattle in Nakula Natural Area Reserve before it was fenced.
Kahikinui strand of trees with very little understory
Non-native ungulates play a large role in modification and degradation of habitat in Hawai’i. Below, we have listed some of the major offenders and their history in the islands. For the protection of our native forests and the preservation of our native birds, removal and exclusion of these animals from high elevation forests is imperative to prevent further and continued degradation. Fencing remaining intact and/or remnant forest patches is effective in regenerating and protecting native forest from the effects of ungulates. Fences must be maintained and feral ungulate populations must be managed.
Watershed partnerships across the islands are managing ungulates and protecting native forest.
Feral Pigs (Sus scrofa)
Pigs were first brought to Hawai’i by the Polynesian ancestors of the Hawaiians; these animals were kept penned and probably didn't do too much damage to local ecosystems. When larger pigs were released by Europeans in 1778, they invaded the native forests and have since caused perhaps the greatest ecological damage of any of the invasive ungulates.
Pigs are omnivorous and eat an extremely varied diet, consuming everything from plants to fungi to carrion. They decimate the understory of native Hawaiian forests, especially of native ferns and lobelioids, being either eating the vegetation or digging it up in their search for food. They may be directly implicated in the extinction of the endemic Po'ouli, which depended on the forest understory as a food source. They carry the seeds of invasive plants such as strawberry-guava into pristine forest in their fur and feces. The pits they leave behind from rooting and wallowing in the earth may also form stagnant ponds that aid the reproduction of mosquitos and the spread of avian malaria.
Axis Deer (Axis axis)
Axis deer were first introduced to Hawai’i in 1868 as a gift to King Kamehameha V and have existed on all the main Hawaiian Islands at some point. Maui's deer invasion began in earnest in 1959 with the establishment of a small population for subsistence hunting that now numbers in the thousands and has spread all over the island. These deer are voracious grazers of forest understory plants including seedlings of native trees critical to the survival of native Hawaiian forest birds.
Feral Sheep and Mouflon (Ovis aries and Ovis musimon)
Sheep were first brought to the Hawaiian Islands in 1791 by Europeans and were originally kept in domesticated herds. They were also introduced to areas such as Haleakalā National Park on Maui and the slopes of Mauna Kea on the Big Island for recreational and subsistence hunting up until 2001. They have become a threat to many native understory plants and the bird communities that depend upon them. Like the other invasive ungulates, they eat and trample the seedlings of native trees, having had an especially devastating effect on the māmane-naio forests of Mauna Kea, home to the endangered honeycreeper the Palila.
Goats (Capra hircus)
Goats were offered as a gift to King Kamehameha I by Europeans in 1793. They spread throughout the islands and grew drastically in numbers. Their insatiable appetite for native plants and the erosion caused by their ability to navigate steep terrain has taken chunks out of native forests on all of the Hawaiian Islands.
Feral Cattle (Bos taurus)
Cattle were also introduced to Hawaii early on as a gift from Europeans to King Kamehameha I. They formed large wild herds that ate their way through native forests on all the islands, often clearing entire areas of forest and creating their own pastures. These feral herds have now mostly disappeared and are no longer a major threat to Hawaiian ecosystems, but they played a huge role in the deforestation of Hawai’i that has led to the subsequent extinction of native forest birds.