Nick Upton / Eurasian beaver (Castor fiber) dam made from cut branches, surrounded by wet woodland. Near Lisaku, Ida-Viru County, Estonia. April.

Nick Upton / Felled conifer trees stacked beside forestry track through mixed forest. Near Muraka Forest Reserve, a rare surviving home for Siberian flying squirrel (Pteromys volans). Near Lisaku, Estonia. April 2...

Nick Upton / Aspen (Populus tremula) with Aspen trunk rot / False tinder conk mushroom (Phellinus tremulae). Trees with rotten cores provide ideal nest holes for the Siberian flying squirrel (Pteromys volans). Mur...

Nick Upton / Researcher radiotracking Siberian flying squirrel (Pteromys volans) in mature mixed forest. Muraka Forest Reseve, near Lisaku, Estonia. April 2018.

Nick Upton / Researcher setting trailcam to monitor Siberian flying squirrel (Pteromys volans) nest hole. Mature mixed forest, near Lisaku, Estonia. April 2018. Model released.

Nick Upton / Researcher using laptop to check trailcam footage of Siberian flying squirrel (Pteromys volans) nest box in mature mixed forest. Near Lisaku, Estonia. April 2018. Model released.

Nick Upton / Nest box for Siberian flying squirrel (Pteromys volans) in mature mixed forest. Muraka Forest Reseve, near Lisaku, Estonia. April 2018.

Nick Upton / Mixed wet woodland including Aspen (Populus tremula) and Downy birch (Betula pubescens). Inhabited by rare surviving Siberian flying squirrel (Pteromys volans) population. Near Lisaku, Estonia. April...

Nick Upton / Mixed wet woodland including Aspen (Populus tremula) and Downy birch (Betula pubescens). Inhabited by rare surviving Siberian flying squirrel (Pteromys volans) population. Near Lisaku, Estonia. April...

Nick Upton / Lisaku Park Forest from above, a mix of mature Fir (Abies sp) trees, Birch (Betula sp) and Eurasian aspen (Populus tremula). Forest host to Siberian flying squirrel (Pteromys volans). Estonia, April 2...

Nick Upton / Siberian flying squirrel (Pteromys volans) caught in emergence trap over nest hole entrance in Aspen (Populus tremula) tree. Muraka Forest Reserve, near Lisaku, Estonia. April.

Nick Upton / Siberian flying squirrel (Pteromys volans) droppings. Found below an old deciduous tree with nest hole. Muraka Forest Reserve, near Lisaku, Estonia. April.

Nick Upton / Laptop screen showing trailcam footage of Siberian flying squirrel (Pteromys volans) returning to nest hole in Aspen (Populus tremula) tree. Near Lisaku, Estonia. April 2018.

Nick Upton / Felled Aspen (Populus tremula) trees with tit nests in hollows. Treeholes suitable for Siberan flying squirrel (Pteromys volans). Near Lisaku, Estonia. April 2018.

Nick Upton / Downy birch (Betula pubescens) trees in mixed woodland, the tree on the left houses a Siberian flying squirrel (Pteromys volans) nest hole. Near Lisaku, Estonia. April.

Nick Upton / Researcher radio tracking Siberian flying squirrel (Pteromys volans) in mature mixed forest. Muraka Forest Reseve, near Lisaku, Estonia. April 2018. Model released.

Nick Upton / Siberian flying squirrel (Pteromys volans) emergence trap over entrance to nest hole in old Aspen tree (Populus tremula). Muraka Forest Reserve, near Lisaku, Estonia. April 2018.

Nick Upton / Researcher radio tracking radio collared Siberian flying squirrel (Pteromys volans). Mature mixed forest, Muraka Forest Reseve, near Lisaku, Estonia. April 2018. Model released.

Nick Upton / Lisaku Park Forest from above, a mix of mature Fir (Abies sp) trees, Birch (Betula sp) and Eurasian aspen (Populus tremula). Forest host to Siberian flying squirrel (Pteromys volans). Estonia, April 2...

Nick Upton / Felled trees stacked beside forestry track through mixed forest. A few metres outside protected limits of Muraka Forest Reserve, a remaining habitat of Siberian flying squirrel (Pteromys volans). Esto...

Nick Upton / Siberian flying squirrel (Pteromys volans) caught in trap, prior to fitting of radio collar. Muraka Forest Reserve, near Lisaku, Estonia. April.

Nick Upton / Researcher labelling collection tube of Siberian flying squirrel (Pteromys volans) droppings. Droppings found below old deciduous tree with suitable nest hole. Muraka Forest Reserve, near Lisaku, Ida...

Nick Upton / Siberian flying squirrel (Pteromys volans) droppings in moss. Found underneath old deciduous tree with an occupied nest hole. Lisaku Park Forest, Estonia. April.

Nick Upton / Felled conifers stacked at edge of forest.Near Muraka Forest Reserve, a rare surviving home for the Siberian flying squirrel (Pteromys volans). Estonia. April 2018.

Nick Upton / Felled Aspen (Populus tremula) trees with tit nests in hollows. Treeholes suitable for Siberan flying squirrel (Pteromys volans). Near Lisaku, Estonia. April 2018.

Nick Upton / Eurasian aspen (Populus tremula) catkins, major food souce for Siberian flying squirrel (Pteromys volans). Lisaku Park Forest, Estonia. April.

Nick Upton / Research team preparing to radio collar Siberian flying squirrel (Pteromys volans) caught in a trap. Muraka Forest Reserve, near Lisaku, Estonia. April 2018. Model released.

Nick Upton / Researcher reviewing trailcam footage on laptop of Siberian flying squirrel (Pteromys volans) emerging from nest hole in Aspen (Populus tremula) tree at night. Mature mixed forest, near Lisaku, Estoni...

Nick Upton / Researcher examining Siberian flying squirrel (Pteromys volans) droppings. Mature mixed forest, near Lisaku, Estonia. April 2018. Model released.

Nick Upton / Researcher wearing thick gloves collecting Siberian flying squirrel (Pteromys volans) from trap prior to fitting radio collar. Muraka Forest Reserve, Lisaku, Estonia. April 2018. Model released.

Nick Upton / Researcher face to face with Siberian flying squirrel (Pteromys volans) whilst setting trap on old Aspen (Populus tremula) tree. Muraka Forest Reserve, near Lisaku, Estonia. April 2018. Model released...

Nick Upton / Researcher collecting Siberian flying squirrel (Pteromys volans) droppings below an old deciduous tree with an occupied nest hole. Muraka Forest Reserve, near Lisaku, Estonia. April 2018. Model releas...

Nick Upton / Mixed wet woodland including Aspen (Populus tremula) and Downy birch (Betula pubescens). Inhabited by a surviving population of Siberian flying squirrel (Pteromys volans). Near Lisaku, Estonia. April...

Nick Upton / Researcher examining and sexing Siberian flying squirrel (Pteromys volans) prior to fitting radio collar. Muraka Forest Reserve, near Lisaku, Estonia. April 2018. Model released.

Nick Upton / Siberian flying squirrel (Pteromys volans) fitted with radiocollar on Aspen (Populus tremula) trunk near nest hole. Mature mixed forest, near Lisaku, Estonia. April 2018.

Nick Upton / Siberian flying squirrel (Pteromys volans) in the hand, prior to fitting of radio collar. Muraka Forest Reserve, near Lisaku, Estonia. April.

Nick Upton / Siberian flying squirrel (Pteromys volans) entering nest hole in Downy birch (Betula pubescens) tree trunk. Mature mixed forest, near Lisaku, Ida Virumaa, Estonia. April.

Nick Upton / Researcher examining and sexing Siberian flying squirrel (Pteromys volans) prior to fitting radio collar. Muraka Forest Reserve, near Lisaku, Estonia. April 2018. Model released.

Nick Upton / Researcher fitting radio collar on Siberian flying squirrel (Pteromys volans) caught in mature mixed forest at night. Near Lisaku, Estonia. April 2018.

Nick Upton / Siberian flying squirrel (Pteromys volans) peering out of nest hole in old Aspen (Populus tremula) tree. Mature mixed forest, near Lisaku, Estonia. April.

Nick Upton / Researcher inspecting a Siberian flying squirrel (Pteromys volans) caught in trap on old Aspen (Populus tremula) tree with occupied nest hole. Muraka Forest Reserve, near Lisaku, Estonia. April 2018....