26 Mar 2019

Want to prevent 131 extinctions? Focus on these islands

Invasive species are a huge threat to island wildlife. A new study pinpoints key islands across the world that we could start restoring right now to help save the maximum number of highly threatened species.

Alejandro Selkirk Island, Chile is one of the highest-ranking islands on the list © Island Conservation
Alejandro Selkirk Island, Chile is one of the highest-ranking islands on the list © Island Conservation
By Jessica Law

Generations ago, your family arrived on the island – borne across the ocean by driftwood or blown by the wind. You scrambled ashore to find a vast, luscious space waiting to be colonised. Down the generations, you forgot about the predators that had imperilled your ancestors. You lost the instinct to fight back or run away, because you no longer needed it. Then, one day, strange alien beings arrived on the island. Creatures you had never seen before and had no idea how to defend yourself from. With no predators to keep them in check, they spread rapidly across the island, feasting upon you and your family.

It may sound like science fiction, but this is the situation for hundreds of species on islands around the globe. Islands are epicentres for extinction: although they comprise only 5.3% of the earth’s land surface, they are the location of 90% of all bird species extinctions since 1500. Invasive species were the major driver of 46% of these extinctions. Cats, rats, goats and pigs among the top threats: introduced by humans either accidentally or deliberately, they continue to have a profound impact on ecosystems. Today, almost three-quarters of threatened birds on islands are impacted by invasive species.

Fortunately, this can be reversed. “Eradicating invasive mammals from islands is a powerful way to remove a key threat to island species in order to prevent extinctions and conserve biodiversity,” stated Dr Nick Holmes, lead author on the study and Director of Science at Island Conservation.

Scripp's Murrelet have dramatically increased thanks to rat removal on Anacapa Island © Shaye Wolf

Past successes have proven it’s possible to bring species back from the brink in this way. For example, following the removal of invasive rodents on Anacapa Island in the Californian Channel Islands, the hatching success of Scripps’s Murrelet Synthliboramphus scrippsi (Vulnerable) shot up from 20% to 90%. The newly-restored island also attracted species that had not been present before – for example, the Ashy Storm-petrel Hydrobates homochroa (Endangered).

As knowledge and experience increases, this success has expanded to islands formerly considered too difficult or inaccessible. For example, in 2018 conservationists scaled sheer rock faces to achieve the first successful eradication of invasive rodents on Teuaua Island, French Polynesia. In fact, island restorations now enjoy an average success rate of 85%.

The conservation world is in a better position to restore threatened islands than ever before – backed up by proof that it can help stem the global extinction crisis. But where should we focus our actions? A huge global collaboration between 50 authors, co-led by institutions including Island Conservation and BirdLife*, has identified 169 islands where vertebrate eradication is technically and socially feasible. If successful, these operations would help to prevent the extinction of 131 highly threatened species of birds, mammals, reptiles or amphibians and benefit 9.4% of the earth’s highly threatened island-dwelling vertebrates. That’s a huge proportion of species for such a small amount of space.

The study in numbers - read the full infographic here:

Steve Cranwell, Programme Manager for BirdLife’s Invasive Species programme, sees huge potential in these findings: “These islands represent an opportunity for dramatically increasing the pace and scale of invasive species eradication. The delivery of these operations is going to require commitment and collaboration by governments, NGOs, funders, local communities and landowners. Active in over 120 countries, the BirdLife Partnership can help influence this change.”

Key islands include Gough Island in the South Atlantic, where the RSPB (BirdLife in the UK) is leading plans to remove a giant strain of invasive house mice to benefit six highly threatened bird species in one go, including the Tristan Albatross Diomedea dabbenena (Critically Endangered). Also on the list is Marion Island, where BirdLife South Africa is raising funds to eradicate invasive mice through a “sponsor a hectare” campaign. Meanwhile, BirdLife Pacific and SOP Manu (BirdLife in French Polynesia) are developing operations to restore six of this study’s top 169 islands at once, which will benefit four highly threatened bird species along with some rare dry forest habitats.

The information gathered for the study was phenomenal in scale. Scientists used biological and geographic data compiled for 1,279 islands worldwide, which are home to 1,184 terrestrial vertebrate species listed as Critically Endangered or Endangered on the IUCN Red List. They also took into account the social and political feasibility of launching a restoration programme, for example whether local people would welcome the restoration, and if the land was privately owned.

The Tristan Albatross will benefit from mouse removal on Gough Island © RSPB

The hard work was worth it. “Identifying these opportunities means that governments, donors and conservation organisations can set priorities more effectively, allowing them to target limited resources where they will deliver the greatest benefits for native biodiversity,” says Dr Stuart Butchart, Chief Scientist at BirdLife International.

Politically, this will have knock-on effects across the whole world, says Dena Cator, BirdLife’s Global Conservation Policy Coordinator. ‘Invasive alien species are one of the main causes of biodiversity loss across the globe and most countries have committed to preventing their introduction and, where possible, eradicating them under the Convention on Biological Diversity. Action to tackle invasive species also contributes to food security, human health, livelihoods and trade, cultural integrity and preserving an established way of life. The 2030 Agenda on Sustainable Development, which was adopted by all United Nations Member States in 2015, recognises the cross-cutting threats posed by invasive species.”

Ecologically, restoring islands also has huge benefits on the ecosystems that surround them. For example, guano produced by thriving seabird populations has been shown to help coral reefs and forests flourish.

Now, like never before, we have the signposts showing us where to focus our action – all we need to do is follow them.

Read the full paper, Globally Important Islands Where Eradicating Invasive Mammals will Benefit Highly Threatened Vertebrates, here.


*The paper was led by conservation biologists from Island Conservation, BirdLife International, the Coastal and Conservation Action Laboratory at the University of California at Santa Cruz (UCSC), and the International Union for the Conservation of Nature (IUCN) Species Survival Commission (SSC) Invasive Species Specialist Group.