A walk with invasive species

In my brief time as an editorial intern for Pasquines in Washington, DC, I spent most of my days off walking around the city. On my walks, I encountered a bird that I found to be startlingly different. It was a European Starling, a bird I had never seen before. It was more than just a pretty sight. The bird is listed on the United States Department of Agriculture’s National Invasive Species Information Center. They are invasive species that cause $800 million in agricultural damage annually. They are also aggressive towards native birds and can outperform them for resources. Personal encounters with invasive species can be quite casual, but their effects can be devastating.

Invasive species are plants or animals that are not native to the environment and cause harm. The harm can be economic, environmental, or damaging to human health. Humans are the primary cause of introducing invasive species to new habitats. Many invasive species may hitch rides from cargo ships. Others are intentionally or accidentally set free into new environments by humans. In these new environments, invasive species can flourish, even at the expense of native wildlife.

Invasive species can be even more devastating for islands in particular. Islands are unique habitats where species evolve and adapt to selective environments. Due to their habitats being surrounded by the ocean, native species have no alternative habitat beyond the island. There are also no additional populations in other locations since species are exclusive to the island. So when they are outperformed or eaten by an invasive species, it’s bad news for the native species. Invasive species are the leading cause of extinction for native species on islands. 

When invasive species take over an island’s ecosystem, it’s not always a definitive end for native species. One species, in particular, may bring a sign of hope. The Guam Kingfisher, known as the Sihek by the indigenous people of Guam, has been made extinct on its native island by an invasive snake. It was not alone in its fall. 10 out of 12 native species of birds on Guam have declined due to the introduction of the brown tree snake. The Sihek has made headlines for its future plans of reintroduction into the wild. But not in Guam. The invasive brown tree snake that made the Sihek extinct in Guam still successfully inhabits it. Instead, the bird will be released on a nearly uninhabited collection of islands called the Palmyra Atoll. 

Introducing the Sihek into the new islands may ironically make it an invasive species on Palmyra Atoll. However, there continues to be careful research to ensure this isn’t the case. The Sihek will be carefully monitored from the beginning at its new home. If the Sihek becomes a problem, it can be quickly removed. Removing the invasive species as soon as possible is the easiest and most effective way to stop an invasive species from spreading. However, once an uncontrolled invasive species establishes itself in its new habitat, it is hard to completely remove it. 

The brown tree snake is native to Australia, Indonesia, and Papua New Guinea. It is thought that the brown tree snake was first brought to Guam accidentally by imported cargo. They were first introduced to the island in the late 1940s and early 1950s. Now over two million brown snakes populate the island. They don’t just decimate bird populations; they also cause costly power outages by slithering across electrical wires. However, the United States has not given up fighting the brown tree snake. Last year the US Department of the Interior’s Office of Insular Affairs gave $4.1 million to the Brown Tree Snake Control program. It’s a small price to pay when you consider the damages. Scientists estimate that the brown tree snake causes $10.3 billion in yearly damages globally. Not to mention the pricelessness of native wildlife eradicated from Guam by the snake.

In most cases managing the invasive species’ population is the best we can do. Extermination campaigns, like the invasive wildlife bounty hunting program in the United States Virgin Islands, can be helpful. However, completely wiping out an invasive species is extremely difficult.

Studies have found that efforts with the best results include functional eradication, which focuses on eliminating invasive species only where they are densely populated in small areas. Programs involving functional eradication of invasive lionfish populations have seen success throughout the Caribbean Sea and the Atlantic Ocean.

If eliminating an invasive species is possible, the ecosystem can recover relatively quickly. One success story comes from removing rats from an Alaskan Archipelago by conservationist programs. The conservationist programs included Island Conservation, the United States Fish and Wildlife Service, and The Nature Conservancy. Rats were destroying the native ecosystem, which included its marine bird population. The rats were removed with a rodenticide deployed from the air over the island. Following the removal of the rats, a study was performed on how quickly wildlife populations could improve. Researchers found that marine bird populations increased significantly after 5-10 years. 

To move forward on controlling existing invasive species populations, it is absolutely important to cooperate with wildlife agencies and support from the government. As science and technology improve, so will our ability to manage invasive species. Until then, I will continue my walks, knowing that some of the nature I experience along the way may not be entirely natural.

Editor’s note: This article has been updated to include that the Brown Tree Snake was introduced between the late 1940s and early 1950s, not the 1980s, as was originally published. We regret the error.