A lioness snoozing in the spring sunshine at London Zoo with her pride. The animals at the zoo are lazing around in the spell of warm weather, but inside the archives of ZSL (Zoological Society London) there is a race against the clock.

ZSL, a wildlife conservation charity, was founded in 1826 and is getting ready to celebrate its 200th anniversary next year. Looking back through its vast archives ahead of the bicentenary, the team found a dusty bank of old film canisters.

Without the means to preserve or project this old film stock their contents are a mystery, but could contain precious historical footage that might help for education or research.

"Whilst we were looking through our archives, we uncovered more than 200, so 230, mystery film reels," says Tina Campanella, the Bicentenary Project Manager at ZSL.

"We have no idea what are on these incredible old canisters, which range from between the 1960s to the 1990s. And we're really looking for support from the public, from anybody who might have the kit or the expertise who can help us digitize them."

This archive footage from the 1930s shows Whipsnade Zoo in Bedfordshire and is one of ZSL's two conservation zoos (the other is London Zoo).

Part of the appeal of these canisters is the mystery they might contain and the treasures that could be unearthed.

"So some of these film reels are black and white. Some of them have sound. Some of them are silent," says Capanella. "And there are clues as to what could possibly be on them, but very cryptic clues. So, one of them here, it just says zoo oddities. I have no idea what that could be. Then we have giant panda mating. So maybe, take a deep breath before we watch that one. "

But ZSL needs to act fast. Much of the film is in good condition but opening some of canisters fills the air with the strong smell vinegar, a tell tale sign of degradation. Vinegar syndrome causes the film to become brittle and shrink and the footage could be lost forever.

Natasha Wakely is the archivist at ZSL and for her it's very exciting to have such a trove of mystery film.

"So it's really, really vast and fascinating as you can expect for an organisation that's been running for 200 years. But one thing we were really missing was footage. And that's why this project to digitise our film is really exciting. We have no idea what is on these film rolls. For example, this one says underexposed bat film. Who knows what that might hold, but that's part of the excitement," she says.

The archive contains many other treasures like a charming nearly 80-year-old cuddly toy of Brumas the polar bear - who was born in London Zoo in 1949, and was the first polar bear born in captivity in the UK.