More than 50,000 geese fly out of stormy Atlantic skies to spend winter on the beautiful Scottish island of Islay, making for one of Britain's most impressive and least known winter wildlife spectacles - thousands of handsome barnacle geese and angel-like families of swans set against magnificent mountain and wild ocean backdrops. Some say the haunting calls of the geese flying at night led to ancient Celtic legends of the hounds of hell yelping as they ran through the skies during very wild storms. The real story is just as remarkable - most of these birds have flown more than 2,000 miles all the way from Greenland. Why should so many birds gather on one small island for winter? And what impact do they have when they all arrive?