From DNA to nest boxes: garden dormice ready for their return to nature

Animal care, genetic research, the right place and the right time: planckendael ZOO prepares endangered garden dormice for a return to nature

Garden dormice, a suitable forest and a moving date. What else do you need to bring an endangered species back to nature? Quite a lot, as it turns out. The garden dormouse is endangered in Flanders, and its habitat is disappearing fast. Every opportunity to help the species counts. But returning animals to nature involves much more than simply moving them to a suitable location. Their health, behaviour, family relationships and genetic background can all affect their chances of successfully establishing themselves. Which animals should be released together? Are they healthy? How genetically unique are the animals currently in our care? And how can we preserve genetic diversity over time? A successful return to nature therefore begins long before the animals are released.

Suitable garden dormouse habitats are disappearing and becoming increasingly fragmented. To help prevent local populations from vanishing, Royal Antwerp ZOO Foundation and Planckendael ZOO use their expertise to care for garden dormice and prepare them for a return to nature. While in our care, the animals receive everything they need and undergo health checks, while scientists map their genetic relationships. This knowledge helps them select suitable breeding pairs and decide which animals can later be released together.

In autumn 2026, the project reaches an important milestone: the first group of garden dormice leaves Planckendael ZOO to be released back into nature.

Between hedgeS and highways

A black Zorro-like mask around its eyes, a long, bushy tail and a preference for life after dark: the garden dormouse certainly looks distinctive. “The garden dormouse isn’t actually a mouse. It belongs to the dormouse family and is more closely related to squirrels,” explains Ben Van Dyck, Animal Care Coordinator. “During the day, it looks for sheltered places above ground, such as hollows in trees.”

To survive, a garden dormouse needs more than one suitable tree or a small patch of woodland. It thrives in varied landscapes with hedges, orchards, shrubs and other sheltered places where it can find food, hide and move around safely.

Even the loss of a single stretch of hedge can cause problems for this endangered species.

And that is exactly where the problem lies in Flanders. Suitable habitats are not only disappearing; changes to the landscape are also cutting them off from one another. “Garden dormice prefer to move above ground, among trees, branches and shrubs. They don’t like travelling across open ground,” says Hans Vermeiren, ecologist at CORRIDOR. “So even losing a small section of hedge can break the connection between two habitats. What looks like a minor change in the landscape to us can make a huge difference to a garden dormouse.”

This decline makes local populations increasingly vulnerable. Releasing animals is therefore not simply a matter of finding a forest and letting them go. They need food and shelter, but also enough space to reproduce and spread further.

HEADING INTO NATURE WITH THEIR NEST BOX

Before garden dormice can return to nature, they go through months of preparation at Planckendael ZOO. During their stay, every animal receives the necessary care and health checks, as well as a microchip so individuals can be identified and monitored later.

But being healthy is only part of the story. Scientists also study the animals’ genetic background and how closely related they are to one another. This reveals which garden dormice are close relatives and where important genetic differences can be found. Genetic diversity helps a species adapt to changes in its environment and can make populations more resilient to disease.

“A group of animals can look perfectly healthy and still be genetically vulnerable,” explains Philippe Helsen, Conservation Genetics Research Coordinator at Royal Antwerp ZOO Foundation. “If animals are too closely related, genetic diversity is gradually lost. We want to preserve as much of that diversity as possible to give the species the best possible chances in the long term.”

Using this genetic information, researchers select suitable breeding pairs. Young dormice are now also being born at Planckendael ZOO, expanding the group. They too become part of the genetic puzzle. “For every animal, we look at how closely it is related to the rest of the group,” Philippe continues. “That information helps us make decisions: which genetic lines can strengthen the breeding programme, and which animals can contribute to restoring populations in nature?”

This autumn, the first group is ready. Around thirty garden dormice will make the move from Planckendael ZOO back into nature. And the animals are not travelling alone. The nest boxes they use at Planckendael ZOO are coming with them. For a garden dormouse, which naturally seeks sheltered places above ground, these provide a familiar refuge in an unfamiliar environment.

The timing is deliberate too. For this first group, the decision was made to release the animals before hibernation, allowing them to spend their winter dormancy in their natural habitat.

For this project, Royal Antwerp ZOO Foundation and Planckendael ZOO are working together with the Agency for Nature and Forests (ANB) and CORRIDOR, each partner contributing its own expertise. “ANB knows and manages the release area, Planckendael ZOO brings its experience in genetics and species conservation programmes, and CORRIDOR has extensive knowledge of garden dormouse ecology,” says Wouter Huygens, forest ranger at ANB. “By bringing all that expertise together, we can take a much more targeted approach to restoring the species.”

Now, it is up to the garden dormice. Their microchips allow researchers to monitor where the animals turn up and how they establish themselves in their new habitat. The use of the nest boxes and the surrounding habitat will also be monitored over the coming months. “Those insights are essential because they allow us to adjust our approach where necessary,” says Ben. “If we see that animals are struggling to establish themselves in a particular area, we can respond, for example by releasing additional animals or adjusting the composition of the group. Factors such as the ratio of males to females and the range of ages within a group also play a role.”

THESE GARDEN DORMICE ARE JUST THE BEGINNING

The project does not end with this first group. More releases are planned in 2027, after hibernation. But releasing garden dormice is one thing. Making sure they are still part of the Flemish landscape years from now is another. Success is not achieved the moment the animals take their first steps back into nature. They need to establish themselves, reproduce and eventually maintain a population without human support..

“In conservation, we always look beyond the animal standing in front of us today,” says Jan Dams, Animal Care Manager at Antwerp and Planckendael ZOO. “Our goal isn’t simply to release as many garden dormice as possible. We want strong populations that can maintain their place in nature in the long term. Every step we take today has to contribute to that.”

The garden dormouse is not only a remarkable animal. It also has its own role to play in the ecosystem.

And that's not just important for the dormouse itself. Every species is part of a larger ecosystem. “If you would ask any forest ranger, of course we don’t want to see a single species disappear from Flanders,” Wouter continues. “The garden dormouse isn’t just a special animal; it also has its place in the ecosystem.” Garden dormice eat fruits and invertebrates, helping to disperse seeds and keep insect populations in check. In turn, they are prey for animals such as owls, martens and foxes. This small nocturnal mammal is therefore one link in a much larger ecological chain.

CONSERVATION KNOWS NO BORDERS

Antwerp and Planckendael ZOO have been working to protect endangered species for many years. Through their conservation foundation, Royal Antwerp ZOO Foundation, scientists, animal keepers and veterinarians combine their expertise to help give species a future. Their work ranges from managing breeding programmes for species such as bonobos and cinereous vultures to field conservation projects in countries including Congo and Brazil.

Conservation might make you think of distant countries and exotic animals. But ecosystems closer to home are under pressure too, often without us even noticing. The garden dormouse is a perfect example.

“Thanks to our many years of experience in conservation, we can act very quickly when needed,” says Jan. “The knowledge and techniques we’ve developed over the years for species such as bonobos, Vietnamese pheasants and cinereous vultures can also be used to help the garden dormouse. From animal care and breeding to the latest genetic techniques, we have a great deal of expertise in-house.”

It is precisely this combination of expertise that allows the care of individual animals to become part of a much broader conservation project. Time is particularly important for a short-lived species such as the garden dormouse, which has a life expectancy of around two to three years. Decisions about breeding, genetics and returning animals to nature sometimes need to be made quickly. In this way, decades of conservation experience from around the world can also make a difference much closer to home.

WHAT THE DNA OF A GARDEN DORMOUSE TELLS US

You cannot tell by looking at two garden dormice whether they are related. Their DNA can. And that information matters when animals are being returned to nature. If mainly close relatives are released together, the next generation will also be closely related. That is why researchers at Royal Antwerp ZOO Foundation are mapping the animals’ genetic backgrounds in detail.

For an initial analysis, they examined DNA from fifteen garden dormice. They studied more than 46,000 unique positions across the animals’ genetic code, creating a kind of genetic fingerprint for each individual. By comparing those fingerprints, researchers can see which animals are closely related and how much genetic variation exists within a group. And the results were striking.

The garden dormice they studied showed clear genetic differences. This demonstrates how genetic diversity within a species can be distributed across different groups. As habitats shrink or disappear, groups of garden dormice can become increasingly isolated from one another. As a result, even a small group can carry genetic variation that is rare or absent elsewhere.

For conservationists, that is valuable information. Genetic diversity that exists today is something they want to preserve as much as possible. And they can put that knowledge to use immediately. The more genetic diversity a species retains, the more options it has to adapt to future changes. Researchers therefore select breeding pairs that are as distantly related as possible, helping to preserve genetic diversity and limit inbreeding.

The genetic puzzle is not complete yet. Scientists are also mapping the genetic background of newly arrived animals and newborn young. This allows them to determine which animals should breed together in future generations and which combinations may be suitable for later releases.

The current results are also being placed in a wider European context by comparing the genetic data with those of garden dormice from other parts of Europe, from the Iberian Peninsula to the Balkans. With every new piece of information, the genetic picture becomes clearer — and DNA helps researchers make better decisions about how to protect the garden dormouse, both today and in the future.