Invasive plant and animal effects on the black- netted stilt (Himantopus mexicanus knudseni) and the black-crowned night heron (Nycticorax hoatil of Hawaii By: Stephanie Woo

 Hawaii is often referred to as the endangered species capitol of the world and the extinction capitol of the United States  After the introduction of non-native species of plants and animals, many of Hawaii’s native species are being lost  Although much of the loss of wetlands is caused by human destruction, alien species of plants and animals have caused many species of native birds and plants to become endangered, and in some cases, extinct

 The alien red mangrove (Rhizophora mangle) and pickleweed (Batis maritima) have altered the environment for the native animal species, especially already endangered bird species like black-netted stilt (Himantopus mexicanus knudseni) and the indigenous black-crowned night heron (Nycticorax hoatil).

 Red mangrove

 Pickleweed

 Exposing new, non-native plants and animals to new environments can be dangerous because they usually have no natural enemies and can quickly take over a large area:

 Pickleweed was introduced in 1859 to Hawaii from South America  Because of its high tolerance for salt water, pickleweed is not eaten by many animals. One of the only animals known to feed on this plant is the white-tailed deer, which is not found in Hawaii, thus explaining how the plant was able to expand so rapidly in Hawaii.

 Another problem with pickleweed is that they have short, dense strands, which prevent important species like shorebirds or waterbirds from nesting on them.

 Red mangroves were introduced from Florida to Hawaii in 1902 to alleviate erosion after the destruction of coastal vegetation  Since the red mangrove has only been living in Hawaii for one hundred years, Hawaiian marine species have not been able to exploit the detritus-based food chain

 The native and endangered black-netted stilt has affected by invasive plant species because it lays eggs on the ground, and pickleweed is not a very good plant to nest in.

 The red mangroves had not been completely invaluable to all species. The black-crowned night-heron nests in the tall tree tops of the mangroves, away from predators

 BUT……there is an animal species that was introduced to Hawaii in 1883 to try and control rats, insects, and other pest species that fed on sugarcane…

 Mongoose!

 After hearing about this method of control, Hawaiians imported the mongoose to control their sugar cane crops as well.  The plan didn't work out too well because the mongoose slept all through the night while the rats were busy eating the sugar cane.

 What the Hawaiians didn’t take into account was the fact that the mongoose eats pretty much any animal. It eats bugs, rats, snakes, lizards, birds, etc.  The increased population of mongooses (because of no natural predator on Hawaii) has been linked to a direct cause of many decreasing animal populations on the islands

 Not true!

 The pickleweed and mongoose populations have been particularly detrimental to the black- netted stilt populations because after laying eggs on the ground, the mongoose can hide under the think mats of pickleweed and hunt the stilt chicks as prey.

 The invasive pickleweed and mongoose have caused stilt populations to greatly decrease in numbers  In 1975, the stilt bird count was 54 birds, but after the management of pickleweed plants, the stilt bird count reached a high of 124 in 1985 (Drigot 2000).

How are the mangrove and pickleweed controlled?

 The marine corps helps by using the AAVs to run over the pickleweed  After rolling over the pickleweed, mud is deposited on top of the weed, so it is forced to grow in a new direction that could take months to re-grow.

 These “moats” made by the AAVs creates nesting grounds for birds like the stilts  But how are mangroves removed?

 After giving jurisdiction to the Marine Corps and Nu’upia Ponds Wildlife Management Area (WMA ) in 1980 to control the pickleweed and mangrove infestation on the island of Oahu, increasing rates of stilt population and night-heron population have been observed.