Image by Marius Cepulis

A simple kind of life

FSC certified since 2004, the park offers 10,000 hectares of unique landscapes and a harbor for endangered species. The sleepiest and the fairest of them all, we are told, is the fat dormouse (Glis glis). With its fluffy tail and long whiskers, it is sure to steal anyone’s heart at first glance. These rodents are simple creatures. All they want in life is to eat and sleep. All they need is hollows in old deciduous trees. But old trees are rare these days and fat dormice are struggling to survive. In Lithuanian forests, large-diameter trees and trees with hollows are protected only in FSC-certified forests.

Image by Marius Cepulis

How it all began

The fat dormouse conservation works started in the Neris Regional Park in 2005, in accordance with FSC regulations. Since then, park ecologists have set up numerous nesting boxes to provide additional habitats for fat dormice. The plump rodent populations are monitored, and the forest undergrowth is kept intact – fat dormice need dense hazel shrubs to move above the ground safely.


Today we will witness the conservation works and, if dreams come true, a fat dormouse in person. They are hard to find, but we are giddy in hopes. Park ecologists and researchers from the Lithuanian Fund for Nature (abbreviated as ‘LGF’ in Lithuanian) will help us in this mission.
Tadas Bujanauskas and Saulius Pupininkas are park rangers–ecologists and our guides for the day. They will show us the annual monitoring works of the fat dormice. Tadas, the senior ecologist, carries something that resembles a wizard staff – it is more than 2 metres high. “We’ll use this stick to unhook fat dormice nesting boxes from trees,” he explains.

Image by Marius Cepulis

A clairvoyant dormouse

We head down to the Dūkšta River Valley and brave through the thickets into the forest. “Let’s check this one first,” says Saulius and cuts to the left. We squint our eyes, but all we can see is a ripple of leaves and trees. Before we know it, the first nesting box is already down in the grass. Saulius picks up a hammer – where was he hiding it? – and removes the roof of the box. “Is there anything in it?” We crowd around the nesting box. Saulius sways the box from right to left, picks out a few leaves and tramples our hope: “No, just an old nest of a starling.”


Every other year the park ecologists, volunteers, and researchers hang up nesting boxes for fat dormice. Today 400 boxes are hidden across the park. “We use the same kind of boxes for both starlings and fat dormice,” Tadas explains. “Some researchers claim that fat dormice are disturbed by competing birds. Ours do not seem to mind running into a bird,” he continues. “In fact, they often eat bird eggs and, on some occasions, small birds as well. They see it more like a home meal delivery service.”

Image by Marius Cepulis

The next box we check is booming with life – wasp life, that is. We hurry past it, countless wooden steps down and deeper into the forest. The ground here is covered with thousands of tiny apples. “Do you see this wild apple tree?” Tadas points high above our heads, “its fruits taste like quince. Fat dormice love to snack on their seeds, that’s why we often place nesting boxes near apple trees.”


Tree flower clusters, acorns, hazelnuts, wild pears, seeds, raspberries, nuts and occasional birds. All of that and more end up in fat dormice tummies. In Lithuania, fat dormice hibernate for seven to eight months, from mid-September to mid-May. Once they wake up, they are on a mission to accumulate enough fat to survive the next hibernation. Fat dormice have a trick up their sleeves, a kind of clairvoyance, one might say. In early spring, they nibble on tree buds and examine the taste. The taste helps the fat dormice foresee a poor acorn and hazelnut harvest, and if so, they have no younglings that year. Having no offspring means more food for adults!

Image by Marius Cepulis

Sleeping Beauties

We continue walking up a hill. One nesting box after another, we find nothing but empty dormice nests and leftover hazelnuts. Where is our sleeping beauty? A path of tiny wild apples and cracked hazelnuts leads us deeper into the forest. Next in line is a nesting box numbered ‘280’. Saulius opens it and shuffles through fresh leaves inside. “We have one,” he whispers. Deep under the layers of leaves, sleeps our first fat dormouse! Fluffy, light gray and annoyed, it glares at us and burrows its little face in leaves. We did, after all, wake it up in the middle of the day.


Fat dormice are nocturnal creatures on a tight schedule: even during their active season, they can sleep up to 21 hours a day. The remaining 3 hours are dedicated to running through the maze of hazels in search of food. “One research paper mentions a fat dormouse that had slept for 23 months,” laughs Tadas while he’s trying to lure the dormouse from its box. To help him, Saulius plays a recording of a squeaking fat dormouse, which sounds like a scooter about to drive off. But the mouse is no fool and soon the park rangers give up. And it is then when the dormouse decides to act. It jumps out of the box and onto Saulius’ backpack, stops to pose for a picture, then jumps on Tadas’ arm and up into a tree. Five seconds is all it takes. We watch its luxurious tail scurry above us from branch to branch until the dormouse stops for a snack. If you had been woken up, then why not start with breakfast?

Image by Marius Cepulis

To bite or not to bite

“That’s a youngling,” says Tadas. “We can tell because his fur is light grey, and the body is oval shaped.” The adults are rounder and darker, with black spots around their eyes. They are also one third bigger than younglings and on average weigh 128 g. “Do you see how easily he moves across branches? That’s because his palms produce a sticky secretion. He’s like Spiderman.” We giggle and squeal, mesmerized by this little ball of fur that occasionally peeks its nose through hazel leaves.


Lovely as they seem, fat dormice can and will bite if scared. “We had to weigh fat dormice for a research project and boy, did we get bitten! You need to know how to hold them correctly,” remembers Daiva, ecologist at LGF. Saulius laughs: “Tadas, is that way you let me open all the nesting boxes?” Despite our excitement, the dormouse shows no interest in us. We leave it to snack and continue the search. The undergrowth here is dense. We climb over fallen trees, branches cracking below our feet.


Four empty nesting boxes, one pagan hillfort and many ancient trees later, we find another fat dormouse. It catapults itself out of the nesting box, uses two of us as a bridge and disappears into the hazel maze. But it’s good that we found it. “Fat dormice are indicator species. It’s not just some theoretical term, on the contrary, it directly impacts our daily work,” says Tadas. Finding a fat dormouse means that the forest ecosystem is balanced. “Recently, in another part of the park, we came across a fat dormouse - for the first time! Now we know that the forest is doing well and we don’t need to meddle there anymore.”

Image by Marius Cepulis

Have you seen my tail?

A true artist awaits in the last nesting box we check. She peeks through her ‘window’, whiskers fluttering like a butterfly, and reflects on the situation. Nine humans and zero foxes. So far so good. She emerges from the box and freezes for a couple of seconds. Is she blending in with the background? No, she decides, and dashes around the box, onto Saulius and his backpack. After a few seconds she’s already climbing up a tree. High above our heads is where the real show begins.


She is a dormouse of many abilities and she’s not afraid to show them. Light jumping and stretching, intense staring and swift sprinting – she can do that and more. We cheer her on and can’t believe our luck. This fat dormouse knows a thing or two about luck as well. “Do you see her tail?” asks Tadas. “Fat dormice are like lizards, the skin of their tails comes off if a predator grabs it. This dormouse has been attacked and she has escaped.” The nightlife in the park is wild: our artist has some exposed tailbones that will soon fall off and she will continue her life as a brave, short-tailed dormouse.

Image by Marius Cepulis

The future

After 40 minutes and a newly found pain in the neck, we bid our farewell to the fat dormouse. What does the future hold for her in the park? As in any FSC-certified forest, in accordance with principles on environmental and high conservation values, endangered species and their habitats are protected. The same principles guard old hollow trees and their microhabitats. Here, in the Neris Regional Park, the fat dormouse conservation work started 15 years ago. The ongoing monitoring results show a stable overall population with natural fluctuations. And there is more good news – as of 1 January 2021, a new FSC National Forest Stewardship Standard of Lithuania has entered into force. In accordance with it, reserved sample areas, such as endangered species habitats, will double to at least 10 per cent of each FSC-certified forest management area. This means more forest will be protected and safe for our sleepyheads and other endangered species.