Non-native ungulates play a large role in habitat modification and degredation in Hawaii. 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 of these animals and exclusion from higher elevation forests is imperative to prevent further and continued degredation. Fencing off of remaining intact and regenerating forest patches is effective in lowering the effects of ungulates on Hawaiian forest birds but fences must be maintained and management efforts made to control feral ungulate populations.
Feral Pigs (Sus scrofa)
While pigs were first brought to Hawaii 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, and also destroy young and mature trees in their ruthless 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 Hawaii 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. However, they were also introduced to areas such as Haleakala 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 mamane-naio forests of Mauna Kea, home to the endangered honeycreeper the Palila.
Goats (Capra hircus)
Goats first set their bearded mouths to the native Hawaiian forests in 1793, having been offered as a gift to King Kamehameha I by Europeans. They spread throughout the islands and grew drastically in numbers. While now reduced by hunting and management, their insatiable apetite 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 Hawaii that has led to the subsequent extinction of native forest birds.