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The Compounding Threats of Invasive Species on the Mona Iguana

Island Conservation Restoration Specialist, Cielo Figuerola shares the success and conservation challenges of saving the Mona Island Iguana from invasive plants and animals.

Invasive mammals including mice, rats, feral cats, and pigs are among the greatest threats to island wildlife, but invasive plants also play a concerning role in the decline of species. On Mona Island, Puerto Rico the Endangered Mona Iguana faces an ongoing threat due to the presence of invasive species including Limeberry Shrubs, Australian Pines, feral cats, and pigs. Together, the threats these species pose is compounded reducing viable nesting habitat for the Iguana.

Although plants might seem harmless to an iguana, the Limeberry Shrub and Australian Pine have encroached on the nesting habitat for the endemic (found nowhere else on Earth) Mona Iguana. These invasive plants have overrun vital nesting habitat and altered the island ecosystem. Since 2015, Island Conservation has been working with the Greensboro Science Center, the Puerto Rico Department of Natural and Environmental Resources, the Center for Conservation and Ecological Restoration:Vida Marina, and the U.S. Fish and Wildlife Service to remove and control the invasive species on the island.

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A Critically Endangered Mona Island Iguana. Credit: Tommy Hall/Island Conservation

The Limeberry Shrub was introduced to the island over 70 years ago and since then has spread across the western coast of the island. Limeberry grows in prime Mona Iguana nesting habitat; compacting the soil and providing shade to the sand below. Additionally, the needles that fall from Australian Pines form thick mats over the ground which native plants are unable to penetrate and Mona Iguana cannot dig through to lay their eggs in the sand. The inability to bury their eggs and the decline in the quality of nesting habitat leaves the Mona Iguanas and their eggs more susceptible to predation.

Over the past 70 years, the Limeberry has spread from an approximate area of 0.01 km2 to an area of 0.55 km2. To understand the spread and impact of the Limeberry, Island Conservation staff and our partners have mapped the distribution and range of the shrubs to develop a plan for control and management. In October 2018, baseline surveys found Limeberry Shrubs were present in over 70% of survey points with 20% of plots being composed entirely of seedlings and saplings.

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Seaside cliffs and caves on Mona Island, Puerto Rico. Credit: Tommy Hall/Island Conservation

In November 2018, the efforts to remove the pine trees and pine needles resulted in 3,000m2 of new nesting habitat for the Mona Iguana. Now, the team is looking to the nesting season from June to August to monitor the nesting activity of the Iguanas using trail cameras. Although there are still Pines present on the island, efforts to remove the pines have shown tremendous results already. The Mona Iguanas have gone from zero nests in the restored area in 2016 to 35 nests two years later—meaning 420 baby iguanas have successfully hatched.

Moving forward the team will implement a Mona Iguana population survey which has not been conducted in 19 years and will inform the ongoing efforts to restore the ecosystem and remove Australian Pines. Hopefully one day, Mona Island will once again be a safe haven for the endemic Mona Iguana.

Featured photo: Mona Island Iguana on Mona Island, Puerto Rico. Credit: Tommy Hall/Island Conservation

About Cielo Figuerola

Cielo is currently finishing her doctoral studies in Ecology and Evolution at the University of Puerto Rico. She has worked with Island Conservation since 2012 to protect endangered species, especially on Mona Island where she works to protect the Mona Island Rock Iguana. Traveling, exploring the outdoors, and discovering the simple but amazing details of the natural world are among the things she enjoys the most.

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