Large scale mammal reintroductions in the UK – what are they and why do we want them?

A What the Heck? series blog.

By Christina Derrick

What are reintroductions and why are they happening? 

Imagine going for a walk in the countryside, what animals might you expect to see? 

Probably some cows, most definitely some sheep, perhaps a red kite, a buzzard or a red fox. If you’re really lucky you might even see a pine marten if you’re in the right part of the UK or a golden eagle, even a beaver or two! What if you could see a bison, or even an elusive lynx while wandering around the woods? To some this might sound far-fetched or even scary but with the rewilding zeitgeist gradually gaining more support and credibility it may only be a matter of time before these idle dreams become reality.

In ecology and conservation, a reintroduction is the act of putting a species back into its ‘historic habitat range’, simply put it’s a place the species used to live before humans intervened. Often reintroductions provide a way for species to get back to those historic habitat ranges where they otherwise wouldn’t be able to do so, due to things like the lack of a land bridge or lack of habitat corridors to the habitats (Some species prefer shelter when they’re moving around and won’t move through open spaces). Reintroductions have happened for decades, be it through global conservation efforts or rogue gorilla reintroductions. Though every reintroduction is different, they all come with some downsides and not all of them succeed. 

The red kite and blue butterfly are good examples of species that once given a helping hand can slowly start to look after themselves after reintroduction. The red kite was globally threatened and severely range restricted in the UK in the 1980s, and the large blue butterfly was actually declared extinct in the UK in 1979, but after coordinated efforts and the translocation and reintroduction of European individuals of these species, both the red kite and the large blue butterfly are once again UK residents. 

In recent years several mammals have become focal points for reintroduction projects in the UK, including Eurasian lynx, European bison, Eurasian beaver and more. Many mammal species proposed for reintroduction were extirpated (removed) from the UK hundreds of years ago if not longer due to a combination of over-hunting, deforestation, and other land-use changes. In fact in a much more recent event, rapid industrialisation and changes in agricultural practices have led to the UK becoming one of the most ecologically depleted countries in the world.

Human society relies on ecosystems and we now understand that biodiversity is fundamental for healthy functioning ecosystems. However, taking a purely passive protectionist approach to nature and biodiversity (i.e. conserving what we have left) will not be enough to solve the ecological crisis we currently face. This is where reintroductions become important as they are a vital tool in the arsenal of a conservationist. 

How would mammal reintroductions help address the ecological crisis?

Mammal reintroductions not only address missing biodiversity in the UK, but they also restore vital ecological processes and functions that are currently missing from our ecosystems.  Since the grey wolf reintroduction programme to Yellowstone it has become abundantly clear that apex predators provide substantial ecological benefits to an ecosystem through the suppression of mesopredators (smaller predators such as fox), control of herbivore numbers, and provision of carrion for scavengers. These effects can quickly spread throughout an ecosystem, reducing the effects of overgrazing on vulnerable vegetation, and allow many other species to thrive if pressure from mesopredators is reduced. This effect is known as a trophic cascade, and in the UK it is hoped that reintroductions of top predators such as the lynx would have a similar effect in woodland habitats, where deer overgrazing is deemed a large contributor to forest habitat health decline.

However, it’s not only top predators that can have far reaching effects on their ecosystem, as cascades don’t always flow from the top down! It is becoming increasingly clear that large herbivores (mega-herbivores) play an important role in increasing ecosystem diversity. For example, through grazing, stomping and wallowing habits, European bison are key drivers of creating mosaic grassland wood pasture habitats, and by opening up areas of woodland they allow associated species like insects, butterflies and reptiles to thrive.  Wild boar do this too. By churning up earth in search of food wild boar make space for annual wildflowers, and shrubs to germinate, as well as creating burrowing opportunities for bees and beetles. So many opportunities for increasing biodiversity!

However, size isn’t everything either! At a mere 19kg the Eurasian beaver is perhaps one of the most significant ecosystem engineer species to have existed in the UK. By digging canals, building dams, and creating dead wood, beavers significantly alter the water flow of rivers, creating a diversity of habitats for life to flourish. For example, in the river Otter beaver trials small pools held more fish and allowed water vole to find refuge from invasive mink. By slowing the flow of water, beaver dams also improve the quality of downstream water by trapping carbon and nutrients leached from fields, and they can also reduce flood risk  too. 

So, by reintroducing mammals across the UK we can upscale our ecosystems, improve their resilience and benefit from nature-based solutions addressing growing environmental issues such as flooding, woodland management and even climate change! Notwithstanding the ecological benefits of mammal reintroductions, there can also be significant economic rewards for the surrounding communities through ecotourism. 

If mammal reintroductions are so great, why aren’t we doing them everywhere?

Mammal reintroductions (or reintroductions in general) aren’t the silver bullet to solve all our ecological problems. Great care must be taken to ensure that the species has a significant chance of success where it is reintroduced and there are several considerations to address namely:

Space and habitat.

The UK landscape has changed over the last few thousand (or even few hundred) years. Over the long term forest cover has decreased, urban sprawl has increased, and fences, motorways and other roads criss-cross the land cutting the countryside up into little chunks that represent a significant challenge for the reintroduction of some large ranging species. However, there are still many areas of the UK physically suitable for the reintroduction of mammals, and with increased focus on landscape scale rewilding and reforesting initiatives many more areas could become suitable.

Cost and logistics. 

Capturing, breeding, and transporting wild mammals from mainland Europe to the UK is expensive, for example the Wilder Blean bison project is estimated to cost around £1 million. A great deal of skill, and expertise is also required both in technical field logistics and navigating the UK conservation legislation which is not set up to easily facilitate reintroductions

Opposition from landowners and other interest groups

Not all mammal reintroductions are controversial, for example the Vincent Wildlife Trust pine martin recovery project in Wales made little in the way of newspaper headlines. However, more controversy exists around proposed reintroductions of predators or other species that have the potential to impact or change current ways of living. 

Given the lengthy periods of time many reintroduction candidates have been absent from the UK, they no longer exist in our cultural memory, that is we do not remember how to live alongside them. When viewed in this disconnected way some of their impacts can be perceived as nuisances or unnecessary risks rather than ‘facts of life’. 

Opposition to mammal reintroductions ranges from fear of injury, predation, the spread of disease to livestock and/or other native species, to worries about flooding of agricultural fields or damage to infrastructure (in the case of beavers). These worries are not always unfounded and for a reintroduction to be successful they must be addressed. This is where conservationists and ecologists need to look outside their own field and collaborate with social scientists, local governments, and the communities surrounding reintroduction areas too. 

Some exciting examples

Despite the myriad of obstacles to mammal reintroductions in the UK there are still some encouraging examples with some creative solutions!

Wilder Blean

As you may be aware, recent proposals to reintroduce the lynx to the UK have been met some staunch opposition, especially from farmers who fear predation. As mentioned above, predator reintroduction proposals are often more controversial than herbivore reintroductions. Even herbivores who weigh a whopping 600 kg! So, while we may be a way off seeing lynx once again roam the UK countryside, we are only a few years away from seeing European Bison! Extirpated from the UK 15,000 years ago and driven to the brink of extinction in the rest of Europe too, four of these giants are set to be released in Kent in 2022. As part of an ambitious project co-led by Kent Wildlife Trust and Wildwoods Trust aiming to ‘rewild’ Blean woods through natural (bison led) woodland management. 


While successful beaver trials and subsequent reintroductions were carried out without enclosures in Scotland, in other parts of the UK the prospect of free release can be contentious (for reasons discussed above). However, that has not stopped the establishment of several successful enclosed trials which have shown the huge landscape benefits of welcoming these creatures back to our waterways. In Cornwall, Devon and Kent small numbers of beavers have been released into enclosures ranging from 3 – 30 hectares where they have been a huge success in restoring wet meadows and fens, and slowing water flow which could be vital to combatting local flooding! 


On the sprawling 3,500-acre Knepp estate, populations of Tamworth pigs are working wonders for the land. The intensive farmland come pioneering rewilding project has used creativity to overcome dangerous animal laws that prohibit the reintroduction of wild boar to the area. Instead they use the rare Tamworth pig as a proxy. Despite being slightly smaller than its wild relative, the pigs grazing and rooting behaviour is helping to boost invertebrate and bird populations on the estate. Knepp now has the largest breeding population of the purple emperor and is the only place in the UK where turtle dove populations are increasing!

To cut a long story short, mammal reintroductions are an incredibly important tool for solving the ecological crisis we currently face. Not only in terms of replacing or reinforcing extirpated or threatened populations of species but also for improving ecosystem health and diversity through the reestablishment of vital ecosystem services. Clearly, context is important and there are a variety of socio-economic and ecological factors that need to be considered when considering reintroductions, a lynx in Hyde park probably wouldn’t be very happy for example. However, the time has come to be proactive, taking a purely protectionist approach to nature conservation is not enough given the depauperate state of UK wildlife. The future is rewilding and we should embrace it!

** End note **

This blog post has focussed on mammal reintroductions however, it should be stated that reintroductions of other groups such as birds, invertebrates, plants, and fungi too. All species have a role to play in their ecosystem and the more there are the more resilient the ecosystem can be.

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