Invasive plant and animal effects on the black-Invasive plant and animal effects on the black-netted stilt (netted stilt (Himantopus mexicanus knudseniHimantopus mexicanus knudseni) and ) and the black-crowned night heron (the black-crowned night heron (Nycticorax hoatilNycticorax hoatil of of

HawaiiHawaii

By: Stephanie WooBy: Stephanie Woo

Hawaii is often referred to as the endangered Hawaii is often referred to as the endangered species capitol of the world and the extinction species capitol of the world and the extinction capitol of the United States capitol of the United States

After the introduction of non-native species of plants and After the introduction of non-native species of plants and

animals, many of Hawaii’s native species are being lostanimals, many of Hawaii’s native species are being lost Although much of the loss of wetlands is caused by Although much of the loss of wetlands is caused by

human destruction, alien species of plants and animals human destruction, alien species of plants and animals have caused many species of native birds and plants to have caused many species of native birds and plants to become endangered, and in some cases, extinct become endangered, and in some cases, extinct

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

Red mangroveRed mangrove

PickleweedPickleweed

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

Pickleweed was Pickleweed was introduced in 1859 to introduced in 1859 to Hawaii from South Hawaii from South America America

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

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

Red mangroves were Red mangroves were introduced from Florida to introduced from Florida to Hawaii in 1902 to Hawaii in 1902 to alleviate erosion after the alleviate erosion after the destruction of coastal destruction of coastal vegetation vegetation

Since the red mangrove Since the red mangrove has only been living in has only been living in Hawaii for one hundred Hawaii for one hundred years, Hawaiian marine years, Hawaiian marine species have not been species have not been able to exploit the able to exploit the detritus-based food chain detritus-based food chain

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

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

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

Mongoose!Mongoose!

After hearing about this method of control, After hearing about this method of control, Hawaiians imported the mongoose to Hawaiians imported the mongoose to control their sugar cane crops as well. control their sugar cane crops as well.

The plan didn't work out too wellThe plan didn't work out too well because because the mongoose the mongoose slept all through the nightslept all through the night while the rats were busy eating the sugar while the rats were busy eating the sugar cane. cane.

What the Hawaiians didn’t take into account was What the Hawaiians didn’t take into account was the fact that the mongoose eats pretty much any the fact that the mongoose eats pretty much any animal. It eats bugs, rats, snakes, lizards, birds, animal. It eats bugs, rats, snakes, lizards, birds, etc. etc.

The increased population of mongooses The increased population of mongooses (because of no natural predator on Hawaii) has (because of no natural predator on Hawaii) has been linked to a direct cause of many been linked to a direct cause of many decreasing animal populations on the islandsdecreasing animal populations on the islands

Not true!Not true!

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

The invasive pickleweed and mongoose The invasive pickleweed and mongoose have caused stilt populations to greatly have caused stilt populations to greatly decrease in numbersdecrease in numbers

In 1975, the stilt bird count was 54 birds, In 1975, the stilt bird count was 54 birds, but after the management of pickleweed but after the management of pickleweed plants, the stilt bird count reached a high plants, the stilt bird count reached a high of 124 in 1985 (Drigot 2000).of 124 in 1985 (Drigot 2000).

How are the mangrove and How are the mangrove and pickleweed controlled?pickleweed controlled?

The marine corps helps by using the AAVs The marine corps helps by using the AAVs to run over the pickleweedto run over the pickleweed

After rolling over the pickleweed, mud is After rolling over the pickleweed, mud is deposited on top of the weed, so it is deposited on top of the weed, so it is forced to grow in a new direction that forced to grow in a new direction that could take months to re-grow. could take months to re-grow.

These “moats” made by the AAVs creates These “moats” made by the AAVs creates nesting grounds for birds like the stiltsnesting grounds for birds like the stilts

But how are mangroves removed?But how are mangroves removed?

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