For more than six decades the Cairngorms have been a safe haven for Britain's only free ranging herd of reindeer.

The Cairngorm Reindeer were first brought over from Sweden to Glasgow by ship more than 60 years ago.

Up until that point, native reindeer had not been seen on British shores for more than 1000 years.

The S.S Sarek took over five cows and two bulls - one named "MacRudolph" - under the guardianship of a traditional Sami herder called Mikel Utsi.

He had visited the Highlands and finding it so similar to his homeland, formed an ambitious plan to reintroduce them to the area.

The reindeer spent time at Edinburgh Zoo in quarantine before being released into the mountains.

Mikel Utsi found the conditions in the Cairngorms were perfect for the animals - the area even had the same type of lichen that reindeer love to eat.

Mikel Utsi believed that the Cairngorms had the right sub Arctic qualities to provide a perfect home for reindeer.

In fact, as the planet has warmed since the ice age, the Cairngorms are now the only place left in the UK able to support such an animal.

Research is currently underway to monitor the herd to investigate the ecological role they play.

Researchers at the University of the Highlands and Islands are using cutting edge GPS camera collars to find out more about the whereabouts and behaviour of the reindeer in the Cairngorms.

Dr Louise de Raad, Inverness College UHI research fellow and principal investigator on the programme, said: "The Cairngorms National Park contains some of the finest forests and mountain habitats in Britain and landowners are seeking to maximise the restoration and expansion of these areas.

"We know the reindeer are a key visitor attraction, but despite being present for more than 60 years we know very little about their impact on the area.

"Studying their feeding and ranging behaviour will be a first step towards understanding their impact and this will help us make recommendations to ensure that the herd is managed sustainably and continues to make a positive contribution to the area."

Today the number of reindeer has swelled to more than 150 and the herd is thriving. They're now under the care of Tilly Smith and her husband Alan, who met and fell in love among the reindeer.

"In 1981 I came up here to assist the keeper who was living here at reindeer house," says Tilly.

"I was completely dumbstruck by the mountains, the scenery was just spectacular, the reindeer were endearing and the reindeer keeper wasn't bad looking either so we got married."

The couple have cared for the animals ever since.

Research suggests that reindeer were native to the area of Scotland around 2000-300 years ago after the ice age, though how long they remained here no-one is able to say.

Though, as Tilly says, in the Orkneyinga sagas the Vikings write that they were hunting red deer and reindeer in Caithness - and that was about 800 years ago.

"Certainly Mikel Utsi felt that he was reintroducing reindeer to Scotland," says Tilly.

The future of the herd will now rest on the next generation of herders, but Tilly, now a proud grandmother, says she is hopeful her family will guard and care for the herd for many years to come.

For more information on the herd, Tilly and her family have written numerous books on their history and visitors are also welcome during opening times.

Details are available on the Cairngorm Reindeer Herd website.