A ‘Stepping-Stone’ Approach to Endangered Species Release

Image Credit: Alina Fisher, Image Cropped, CC BY 4.0

Optimizing release strategies: a stepping-stone approach to reintroduction (2019) Lloyd et al., Animal Conservation, 22.

The Crux

Restoring endangered species through breeding the species in captivity has become common practice over the last century, and has led to the successful recovery of many species. But the process is complicated, as there are always dangers inherent in releasing species that have become used to captivity back into the wild.

This week’s researchers wanted to test a new approach: rather than releasing species directly back into an area where they have disappeared from, they wanted to first release individuals into an already-occupied habitat patch, where predators and prey were present but the species had a high survival probability. This would be a stepping stone before a second release, intended to restore a population in a new area.

What They Did

The species here is the Vancouver Island marmot (Marmota vancouverensis), found only in the mountains of Vancouver Island, Canada. Conservation breeding started in 1997, with the wild population dropping below 30 in 2003. Marmots from four different Canadian institutions were transferred to one of the institutions, the Mt. Washington Marmot Recovery Centre, to undergo a period of quarantine before release.

Some of these marmots were then released for a year into a safe area on Mount Washington, Vancouver Island – the ‘stepping stone’. They were then released into a more challenging area on Vancouver Island, along with captive marmots who had not been exposed to the stepping stone, and wild marmots translocated from Mount Washington. These groups enabled the researchers to compare survival.

The researchers then modelled the survival of each marmot group against the release type, as well as the year and location of release.

Did You Know: Species Tracking

GPS technology has come a long way in recent years, and it has benefited ecologists enormously. This study utilised radio tracking on the miniscule marmot. But the size of radio trackers in the past often made them unethical. Australian Rakalis were notorious for being able to remove almost any radio tracker. However with advances in technology have come significant advances in our understanding of animal movement. Sirtrack in New Zealand are now able to place a radio tracker on a dragonfly.

What They Found

Marmots released into the stepping stone environment had high survival rates initially. These dropped when they were translocated to the wild, but rebounded after a year, coming close to the other wild marmots. Captive marmots released directly into the wild, however, had low survival rates for the first two years before rebounding, suggesting that there is potentially a two year acclimation period for the species.


The experiment required a very specific type of habitat. It needed to have predators and prey, but not so many that the marmots are likely to be hunted at natural levels. In this experiment, human activities on Mount Washington kept predator levels low. This sort of habitat is not always possible to locate, especially for larger species.

So What?

Being able to increase the survival rates of captive-bred species is obviously a huge boost. As highlighted above though, this method is not simply possible for all species. However it does give conservationists a clear avenue forward for further research.

And lastly, studies like this really highlight the role human land use clearance plays in lowering species survival rates. The larger the suitable habitat area for a species, the more likely we are to be able to find suitable stepping stone environments for them.

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