Despite its relatively tiny 170-square-kilometer (66-square-mile) stature, Floreana Island in the Galapagos hosts an abundance of biodiversity that’s found nowhere else on Earth. Here, feral cats and invasive rats threaten the existence of the Floreana mockingbird like many of the island’s unique inhabitants, inspiring a global network of researchers and conservation organizations to call for the culling of such invasive species.
Removing non-native invasive mammals such as rats, cats, goats, and pigs is a proven conservation tool and could improve the survival rate of almost 10 percent of the Earth’s most highly threatened, land-dwelling, island vertebrates, according to research published in PLOS One. In particular, islands would especially benefit from such eradication efforts. Though they represent just a small proportion of land area on Earth, islands have hosted three-quarters of known bird, mammal, amphibian, and reptile extinctions since 1500. Though there are just under a half million islands on the plant, more than one-third of critically endangered animals call them home today.
“Eradicating invasive mammals from islands is a powerful way to remove a key threat to island species and prevent extinctions and conserve biodiversity,” said Nick Holmes, lead author on the study, in a statement. “This study is an invaluable global assessment of where these future conservation opportunities exist and support regional and national decision-making about where and how to prevent extinctions.”
Invasive mammals – cats and rats in particular – devour the eggs of endangered species like the Floreana mockingbird, as well as prey on young and adult native animals and plants, while spreading invasive seeds and destroying vegetation. Previous efforts show that eradicating invasive mammals on islands for conservation purposes has a success rate of around 85 percent, many of which have resulted in recovery stories of biodiversity loss prevention. The study develops a conceptual framework to identify important islands where removing invasive species may prevent extinctions of some of the most highly threatened animals.
On Ecuador’s Floreana Island, for example, the eradication of feral cats and invasive rats would remove external pressures threatening the critically endangered Galapagos petrol, a seabird that burrows its nests and is dependent on the island for safe breeding. Additionally, the authors write that removing invasive predators will also allow for the reintroduction of 13 locally extinct species.
Gough Island, located 3,100 kilometers (2,000 miles) off the western coast of South Africa, is vital nesting habitat for a number of species, including the critically endangered Tristan albatross and Gough bunting. Here, removing invasive house mice would be a critical step in protecting these species and furthering the preservation of the island, which is designated as a UNESCO World Heritage Site. Similarly, removing feral goats, rodents, and cats on Alejandro Selkirk Island in Chile would remove threats to habitat loss and the predation of a small critically endangered songbird, Masafuera rayadito, endemic to this remote island and found nowhere else in the world.
"Through the UN Convention on Biological Diversity and the UN Sustainable Development Goals, the global community has agreed to halt the loss of biodiversity and preventing extinctions by 2020. Eradicating the non-native invasive species on the priority islands identified through this research would significantly contribute towards meeting this important target,” said study co-author Piero Genovesi.