Camille Coffman-Researcher
Tom Schambow-Writer
Brianna Crowe-Programmer
Invasive Animal Species in Hawaii
A variety of problems have resulted from numerous introductions of nonnative animal species in the state of Hawaii. When the first explorers
stepped on land almost 1600 years ago, nearly 90 percent of the species were
unique to the island. While many of these invasive species served an
immediate purpose, often in the long run they created more problems than
solutions. Four animal species, the Small Indian Mongoose, feral pig, African
snail and rats have caused many problems throughout the state and continue to
impact the environment in large ways.
The Small Indian Mongoose was originally introduced to numerous islands
throughout the world, including eight pacific islands and Hawaii in 1883.
Originally, they were confined to their native range of Southeast Asia, but
after rat populations spiraled out of control on oceanic islands, the
mongoose was introduced. At first, the mongoose did an effective job
destroying the out of control rat population. Rats were shown to not be
overly controlled by mongoose, since rats are nocturnal and mongooses are
diurnal, though the mongoose was eventually made irrelevant with the
introduction of better rat poisons. Unfortunately, mongooses eat a variety of
other animal species, including many reptiles. Reptiles were shown to be a
large part of mongoose diet when 23 mongooses were examined near Pearl
Harbor, O’ahu. Additionally, the mongoose has preyed upon eight federally
listed endangered bird species in Hawaii, including the state bird, the
Hawaiian Goose. In fact, land managers in Hawaii often see signs of mongoose
predation on protected birds in mongoose scats. The mongoose and feral cats
of Hawaii have been shown to coexist together, and are often observed sharing
the same food at artificial feeding sites. Both of these invasive species
have learned to peacefully co-exist with each other in Hawaii.
Another animal, the feral pig, was introduced by both Polynesian and
European settlers as a source of food. The pig population has made a great
impact on Hawaii and its surrounding islands. In fact, pigs have been called
“the single largest threat to native species—even the entire natural
community” according to wildlife biologist Jack Jeffrey. They have mainly
caused widespread environmental destruction. The national park service has
done several studies on the impacts of feral pigs in Hawaii. One study
assessed one of Hawaii’s last wild areas, the Kipahulu Valley. The valley,
before becoming a protected area, was overrun by a large feral pig
population, devastating the prime ecosystem. As the pigs overran the forest,
invasive plant species, like the Strawberry Guava Tree, began to dominate the
ecosystem. After the park service eradicated the entire pig population,
native species once again covered the majority of the ecosystem within only
four years. Furthermore, a portion of the valley was fenced off with hogproof wire to keep outside feral pigs from reentering the valley.
The pigs
have even been linked to avian disease and the endangerment of Hawaiian
birds. Mosquitoes, which are carriers of the disease, have more breeding
ground in high pig population areas. When pigs eat a fern tree’s core, the
hole left often fills with standing water, which then provides mosquito
breeding grounds. In turn, this high mosquito population hurts the endangered
bird population, as well as the high pig population destroying the bird
habitat. In fact, many places have suffered worse fates than this. Many of
the forests in Hawaii and its surrounding areas have been destroyed to a
point where they will never return to their original state for thousands of
years, all due to destruction by feral pigs. The problems of species
eradication stem from one of the main engines, feral pigs. It is difficult to
control invasive plant species and other animals until the pig population is
under control. While pigs are important to native Hawaiian populations, as
long as they still have a presence in the island chain they will rapidly
continue to push out and endanger other native species. Eliminating the pig
population is difficult however. Fencing has been a large implement used to
control pig destruction of forests, but in itself does not eliminate the
population. Additionally, pig control has been restricted by a large amount
of animal rights activists in the state of Hawaii. The survival of Hawaii’s
native animal and plant species is crucial to the elimination of the feral
pig, but an effective way to destroy the population still has yet to be
found.
With one of the highest populations of invasive animals in Hawaii, rats
have had a great impact on Hawaii’s flora and fauna. Rats first became
present in Hawaii and its islands in the 1700s when the first ships made
their way to the islands. Rats have been effective at destroying native plant
species, since they feed on many plant parts that reduce the chance of plants
surviving. Studying the impacts of rats on indigenous populations may be
difficult however, because they often feed on non-native snail species. In an
experiment looking at the number of snails eaten by rats, the results
indicated high consumption rates of snails by rat populations. In cages with
one rat and 10 snails, an average of eight snails were killed and eaten by
the rat, compared to the control, with no rats and zero snail deaths.
Controlling the rat population is a difficult task, but the technology of rat
poisons have increased.
In addition to the high rat populations, high African Snail populations
also accompany the rat on the Hawaiian Islands. Rats and snails have
overlapping diets that often interact with each other. Snails feed on the
large amount of available plants on the island. Additionally, the rat feeds
on the snail population, creating an interacting chain.
While these four species have made large impacts on the Hawaiian
Islands, a variety of other nonnative species continue to create problems for
the islands. These species have become difficult to eliminate and we cannot
fully estimate the dramatic effects these species have on the island and its
native populations. Further research and funding is needed to fix these
problems and eliminate invasive species in order to preserve and protect the
native Hawaiian species.