Underground worlds caught on camera
The secretive underground lives of British mammals have been captured on camera by filmmakers.
Full-scale rabbit warrens, vole burrows and badger sets were crafted in order to film previously unrecorded details.
The team were able to capture intimate views of family life for some of Britain's best loved, and least understood, species.
The results are revealed in the BBC Two series The Burrowers: Animals Underground.
The resulting footage revealed previously unknown insights: from where water voles locate their latrines to how unrelated badgers establish social bonds.
In the past, underground filming has been limited by natural conditions. The lack of light forced filmmakers to use infra-red cameras that only produced black and white footage, for example. The claustrophobic nature of underground dwellings also makes it difficult to follow animals without disturbing them.
The filmmakers overcame these challenges by consulting with zoo architects, model makers and experts in underground species, then building artificial burrows based on those found in the wild.
They even made a cast of an entire wild rabbit warren found in the grounds of Bicton Park, a stately home in Devon.
Rabbits had previously overrun the grounds of the home, and been expertly culled, leaving an empty warren.
Concrete was poured in to create a cast which when excavated from the soil revealed a complex network of tunnels, chambers and dead ends.
"It was about the size of a tennis court," said Executive Producer Edwina Silver of Dragonfly TV, who created the series for the BBC.
"It was like an installation that wouldn't really look out of place in the Tate."
This structure informed the design of a special studio set up on the land of farmer and water vole expert Derek Gow.
To keep the animals free from danger and disease, the studio burrows were constructed from concrete, foam and removable glass panels. Cameras could film through these panels which could also be removed if the animals were in any trouble. The rabbits also had ample outdoor space to explore and dig.
The filmmakers populated the artificial burrow with domestic rabbits, as wild rabbits were too sensitive to the presence of the cameras and camera operators.
Once the domestic rabbits established their own routines, their behaviour quickly mimicked that of their wild counterparts, said rabbit expert Dr Sasha Norris who consulted for the series.
The filmmakers also built a new home for water voles on Mr Gow's land.
"Filming them in their burrows in a wild situation is impossible because the burrow systems are extremely complex, they're protected so you would need a licence and they're completely dark so you're not going to see anything down there," he explained.
The internal structure of water voles' homes was so little known, the team had to experiment in order to create a replica for the studio.
The team introduced wild voles into boxes of sand and studied the kidney-shaped chambers and connecting tunnels they constructed. These were used as a template to reproduce the animals' natural riverbank habitat.
The wild water voles quickly settled into their new home.
"When we provided them with an outdoor and an indoor environment, we thought they would build nests in the outdoor environment and not come indoors at all," said Mr Gow.
But the voles seemed happiest with the dry, warm environment inside. The team and experts alike were surprised to see how fastidious the animals were in arranging their homes.
"They got materials in from outside, made intricate nests, set up food stores in there... they settled in there very well," said Mr Gow.
Elsewhere in the West Country, filmmakers also focussed on a young foster family of rescued badgers in a set that was specially built beneath a tree.
Unwilling to disturb an existing family of badgers, filmmakers decided to assemble a group of orphans and record their reactions to both the artificial set and life in a foster-family.
To shed light on the underground lifestyles, the team used light-emitting diodes (LEDs) that did not affect the temperature and could be gradually altered without disturbing the animals.
"One of our missions was to bring light to a dark world," said Ms Silver. "In the past there has only been grainy black and white footage. We were determined to do it in colour and we managed to do that."
The Burrowers: Animals Underground begins on Friday 16 August 2013 at 2100 BST on BBC Two.