26 Mar 2019

Science Spotlight: Prioritizing invasive species removal to prevent extinctions

A new study has found removing invasive mammals from 169 islands would improve survival prospects for 9% of the world’s most highly-threatened vertebrates on islands. Our Global Science Coordinator Ian Burfield explains the study and its implications for conservation.

A landscape on Gough Island, where invasive mice will soon be removed. © Ben Dilley
By BirdLife International

You can read the study mentioned in this interview at PLoS ONE.

What inspired this study?

We’ve known for a long time that many of the world’s most threatened species are on islands. We’ve also known that the reason a lot of those species are highly threatened is because of invasive alien species (IAS) that have been introduced (either deliberately or accidentally) to those islands by humans. So what motivated this study was the desire to prevent extinctions and save threatened species by identifying opportunities to effectively and feasibly tackle the threat from IAS.

Why do invasive species pose such a threat on islands in particular?
A lot of species on islands have evolved in the absence of predators. They therefore have very few defences against invasive alien species. Coupled with that, islands often lack the predators that keep alien species in check, allowing them to expand rapidly on the islands. So not surprisingly, you often get very dramatic impacts when species that aren’t supposed to be on islands are introduced. There’s a huge history of extinction, of birds and other wildlife just getting wiped out by invasive alien species.

What’s the significance of identifying the most important islands for eradicating invasive species?
We know from the last few decades that it’s increasingly feasible to clear larger and more technically demanding islands of invasive alien species. There are some amazing examples of what happens, with flora and fauna that were on the verge of extinction immediately starting to bounce back within a year or two of eradication. Additionally, there’s around a 90% success rate for these efforts, so we know it’s a really effective technique. However, as with everything else in conservation, there’s a limited amount of resources, so you have to prioritise. What we tried to do in this study, therefore, was to identify the most important islands worldwide for eradicating invasive mammals, in order to support those responsible for setting priorities and making decisions at relevant scales.

So how did you go about gathering that information?
BirdLife teamed up with other organizations including Island Conservation, the University of California Santa Cruz, and the IUCN SSC Invasive Species Specialist Group. Together we made a comprehensive assessment of all threatened terrestrial vertebrates on islands – birds, mammals, amphibians, reptiles – and compared that to which islands host the invasive mammals threatening them. We developed a framework considering the extinction risk of threatened species, how many islands each species occurs on, the severity of the impact of the invasive species, and the technical feasibility of an eradication. We also looked at the socio-political feasibility of the eradication, taking into account things like whether each island is inhabited by humans, how supportive they would be of eradication, and land ownership. We asked experts to score how feasible it would be to attempt an eradication in the short term (by 2020), the medium term (by 2030), or not in the foreseeable future. We did this for 1,200 highly-threatened vertebrate species and 180 invasive mammal species on 1,300 islands worldwide.

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What were the conclusions of this study?
We identified about 300 islands where eradicating invasive mammals would benefit highly threatened vertebrates. Factoring in socio-political feasibility, we identified 169 islands considered feasible to plan an eradication by 2020 or 2030, which would improve the survival prospects of 9% of the world’s most highly-threatened terrestrial vertebrates on islands. At the top of that list there are 107 islands in 34 territories where it was considered feasible to initiate an eradication project straight away.

What are the implications of this for conservation then?
Concentrating efforts to eradicate invasive mammals on those 107 islands would benefit 151 populations of 80 highly-threatened vertebrate species. This information should now be integrated into national and regional priority-setting as globally important islands where we could have a big impact by conducting eradications, thereby contributing to global goals to reduce biodiversity loss.