ABOVE: A Tasmanian devil

Earlier this month, an environmental organization announced it had released 26 Tasmanian devils (Sarcophilus harrisii) into a sanctuary north of Sydney as part of a project to reintroduce the species to the Australian mainland, where it has not existed in the wild for about 3,000 years. The Scientist spoke with John Ewen, a conservation biologist at the Zoological Society of London who is not involved in the Tasmanian devil project, about how scientists figure out when reintroducing a species is desirable and feasible, and what factors play into the success of such efforts. Ewen’s research focuses on how to prevent critically endangered species from going extinct, often using conservation translocations as a tool.


The Scientist: How far do you go back when thinking about how an ecosystem is supposed to be, in terms of what species should be...

John Ewen: That’s a real challenging question. The way that I would approach it, and I would recommend groups approach it, is to think about what they want to achieve, because there is no defined line that we would ever state is the best place that we want to try and restore to if we’re doing restoration. So I think what we need to be is clear about what state we’re aiming to get to. Often places like Australia . . . and New Zealand might argue that they want to go back to a pre–European colonization state. But these are all rather arbitrary. And they all have to then reflect back on what we value, what we want to see in these systems.

TS: Can you give me some examples of what kinds of values people are looking at when they’re making those decisions?

JE: If we are in a system which is heavily degraded, and we know that it’s been degraded, because of our activities in our system, then often there’s an attraction to try and restore things to before human impacts caused damage. And that can be quite difficult in places where humans have been there for a very, very long time. And so in some oceanic islands—like New Zealand, for example, or Mauritius—there is a much easier line that you could . . . say we could try and restore things to recover the damage that humans did to the system. That’s one quite common value that people will use when they start talking about restoration. 

I am a member of the IUCN’s [International Union for Conservation of Nature’s] conservation translocation specialist group. And they have a set of formal guidelines which can help practitioners decide whether they should do something and how they can best go about determining whether it’s the right choice, and the wording that they use. And the wording that they tend to use is if you’re focusing in on a particular species, and you’re talking about reintroduction, then you’re going back [and] putting a species back into its indigenous range. And then they have a definition for what indigenous range means, and it’s quite broad. It means that there could be some verbal or written record that the species was once found in that space; there could be some physical evidence that the species was found in that space sometime in the past. Even in the absence of all of that, if that space is in close ecological proximity to where the species was known to be, then that could also be justified. There is no strict timestamp on any of that definition. 

See “Researchers Aim to Reestablish an Ancient Fish in an Ohio River

TS: What is the furthest back you’re aware of one of these reintroductions going, in terms when the species was last there?

JE: I think that that Tassie devil one is a pretty impressive one. They’re saying 3,000 years since there was last evidence of Tasmanian devils on mainland or continental Australia. That’s a long time.

TS: In thinking about whether a species would be successful in a place, do you account for whether the climate has changed since they were last in that area? And how do you figure out if they might still be able to live there?

Some of the early successes—peregrine falcons are a fantastic example, Arabian oryx, golden lion tamarins, California condor . . . bison in the US . . . are the poster child, if you like, for reintroduction biology that we all look to.

—John Ewen, Zoological Society of London

JE: This is one of the one of many tricky challenges when it comes to conservation translocation. When a species is lost from a system, something’s gone wrong, and oftentimes, we’re not entirely clear what exactly were the key drivers of the past extinction. Compounding that, the longer the time it’s been since that extinction event and when you’re trying to put the species back, a whole bunch of other things in that ecosystem could also have changed. And so there’s this significant challenge of uncertainty and very complex ecosystems that we’re working within. You have to confront that and try and make the best decisions that you possibly can. 

I think that systems like the Australian mainland have changed a lot in 3,000 years. And I’m not sure that we’ve got a complete understanding of what caused the Tasmanian devils to be lost in the first place—a lot of environmental change, and then a lot of environmental change and degradation . . . has continued since. So there’s some pretty big challenges ahead in that program. That said, I think, from what I’ve seen, [that] they’re going about it very carefully, and in a very controlled way. So I suspect that they’ve got the best possible chance of success—at least within the constraints of what they’re doing now, which is small fenced areas, where the animals are well-protected and well-provided with food. . . .

This challenge of climate, as well, is a problem. And it’s particularly a problem with either highly fragmented landscapes or on islands where animals can’t move, they’re kind of stuck, and so if the climate shifts, or changes such that it’s no longer suitable, then their only option is to adapt, or move. If they can’t move, we can move them. 

See “After Relocation, an Endangered Species Stops Avoiding Predator Scents

A hihi (stitchbird)

There are some nice examples of where people have modeled future climates and tried to incorporate that into translocation planning. The species I do most of my work on is in New Zealand, it’s the hihi [Notiomystis cincta]. . . . A PhD student of mine [Alienor Chauvenet] did some work where we modeled the dynamics of the population against fluctuations in temperature and humidity through a 20-year dataset since reintroduction, and then used that to look at how the dynamics of the population were influenced by fluctuations in temperature. Then we took the future climate scenarios that have been produced and modeled what the fate of our current populations would be, and then also used that to start looking at where suitable habitat might be. So where that climate envelope was, was suitable in 50 years, in 100 years’ time. We showed that there’s a southward shift in New Zealand for suitable habitat, and that our current sites were no longer going to be suitable by 2100. So we have recommended there to move the birds outside of historic range. 

There’s another neat example, [with] the western swamp tortoise, they did something similar in Western Australia, using species distribution models and climate envelopes, looking at successful embryo development, and showing that there was a shift. And so they have actually undertaken translocations of swamp tortoise outside of historic range for that exact reason. So there’s some good examples out there that factor in changing climate. I’d still say that they’re few and far between compared to how many conservation translocations are being done, which is a lot. I think most people’s mindsets are on a much shorter time frame. 

TS: Can you give me an example of a reintroduction that has gone really well, and what factors you think might have contributed to it being a success?

JE: There’s some fantastic examples of species restoration using some form of conservation translocation. And I think this is part of the reason why that conservation tool is so attractive for people to use. Some of the early successes—peregrine falcons are a fantastic example, Arabian oryx, golden lion tamarins, California condor . . . there’s bison in the US. These early iconic reintroduction programs, which were well planned, well resourced, and well followed through with supportive management, are the poster child, if you like, for reintroduction biology that we all look to, and we look to those successes and try and repeat them in an ever greater frequency. They’re such a popular management tool these days.

TS: What are some other things that people can do in planning and in follow up to make sure that reintroductions succeed?

JE: How I always engage with groups that are interested in pursuing a conservation translocation is really to get them to think carefully about what it is that they’re trying to do, because there’s lots of different motivations behind why we want to use conservation translocation, and only part of it will be actually the recovery or restoration of the focal species that you’re trying to move. Increasingly, these days, we’re talking about a rewilding context, and so it’s much more the functional roles that these species are playing. 

We also have to realize that we’re not the only players or stakeholders that are involved in the game. Conservation biologists bring with them their own set of values, where we are very passionate about biodiversity. . . . But there are plenty of other users of the same space that have different motivations, and we should be very careful that we recognize those and combine them into a good plan. One . . . is recognizing that indigenous peoples, who also live [on] and share the land, have their views around resource management and land use, and the classic Western approach to conservation often, I think, forgets about that. And so we need to be much more holistic in embracing pluralistic values. The opening of the cage door is just the beginning of a very long journey to recovery.

The opening of the cage door is just the beginning of a very long journey to recovery.
—John Ewen, Zoological Society of London

Funding is another big one. I mean, there’s this issue that conservation translocations are incredibly attractive things to do, they’re very hands on, they’re very visible, people love them, and audiences love them. They’re also incredibly challenging, incredibly uncertain, and almost always very expensive. And the opening of the cage door is just the beginning of a very long journey to recovery. We’ve reviewed literature on case studies of conservation translocations where one of the biggest problems that people faced [was] not planning properly around the commitment of resources in the long term for recovery. So things go very well for the first year, and then resources run out, and you’re in all sorts of trouble. 

TS: Do people ever reach a point where they can go, ‘Okay, this species is reintroduced, it’s doing well, our role here is done’?

JE: Yeah, and it will be very case-specific. But there’s some fantastic examples; one that pops into my head immediately are things like red kite in the United Kingdom. The recovery following the release of birds into the UK has been incredible—there’s thousands of those things flying around now, and no management required. In New Zealand, we’ve got a lot of forest birds which, despite having to have these mainland islands—these big fancy fenced areas of forest where we keep out the invasive alien predators, mammals—a lot of those birds do fantastically well once you’ve removed the predators. Or we can maroon them on islands where we’ve removed the predators. In many cases, there’s a key threat and we can manage it, mitigate it, and then the birds or animals do fine. And then there’s lots of other cases where it’s not that simple, and so you need to continue providing management support. 

TS: Are there top candidates, or maybe one top candidate, that you’d really like to see reintroduced somewhere?

A sihek (Guam kingfisher)
© istock.com, michael fitzsimmons

JE: Right now, I’m helping a group in the USA think about returning Guam kingfisher to the wild; it’s an extinct-in-the-wild species. That story’s tragic; [the species is] endemic to Guam and Guam had the invasive brown tree snake arrive shortly after World War Two. That tree snake decimated the whole avifauna of Guam and caused a series of extinctions. Two species were rescued into captivity, the Guam rail, or ko'ko', and then the Guam kingfisher or sihek. 

A few years ago, they started releasing the Guam rail [onto islands near Guam]. And recently it’s been downlisted on the IUCN from extinct in the wild, which is a fantastic success story. We want to do the same for the sihek, or the Guam kingfisher. We’re very actively working now to try and get birds back out of the cage from [the] continental US back somewhere in the region, and in the wild. That one is such a challenge that gets into this whole other interesting space, that conservation translocations are not just about restoring something or putting something back where it was. We’re recognizing now that we’re damaging the planet quite drastically—we have these challenges of climate change—which means that past range may not be future-suitable range for a given species. So we actually have to go outside of that historic context if we want to restore species or systems in habitats which will be suitable in the future. [With] the Guam kingfisher, it’s not climate that’s changed, it’s [that] currently the landscape on Guam makes it unsuitable because of the snake. Until we can figure out how to control the snake, we might have to find a different home for the kingfisher. 

See “Researchers Look to Sex Pheromones to Trap an Invasive Snake

That also raises a lot of risk and challenge, right? If you start putting species outside of historic range, then you’ve got to be very careful about what you’re doing.

TS: You mean you’re looking at other islands near Guam?

JE: Yeah. We are, at the moment, looking at other candidate sites—that will be initially an assisted colonization to a new site where they’ve never been before, but it will be in the wild so that we can grow bigger populations than what we can in zoos, and, of course, we prevent all of those chronic problems of adaptation to captivity and chronic genetic drift and inbreeding, which occur because the population is tiny. . . . Remembering that we’ve always got that primary dream to reintroduce sihek back to Guam, and back with the local people on Guam. But that’s just a vision that’s going to take a long time because we’ve got to fix the snake problem first.

Editor’s note: The interview was edited for brevity.

Correction (October 21): This article has been amended to state that there are now thousands of red kite in the UK, rather than tens of thousands, and to include Alienor Chauvenet's name.

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a Tasmanian devil peaks out of a hollow log

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