The first results of a major survey of bird migration are revealing dramatic and unexpected changes in the numbers and timing of some long-distance migrants coming from Africa.

Continuous records made by the Fair Isle Bird Observatory for more than 60 years show that spring migration has got much earlier in recent years for many species, such as the swallow, which is arriving up to three weeks earlier. But, much more surprisingly, for some species, such as the willow warbler, spring migration has got much later.

In addition, considerable changes are apparent not just in the timing of spring bird migration, but also in the timing of migration in the autumn. For example, autumn migration of house martins has got progressively later while that of the swallow has got earlier, again by up to 3 weeks, compared to 60 years ago.

Dr Will Miles, of the Fair Isle Migration Project, presents some of his initial findings at RSPB Scotland's Big Nature Festival, Musselburgh on Saturday 23rd May. The Migration Project is a scientific collaboration between the Fair Isle Bird Observatory Trust and the University of Aberdeen.

Dr Miles says, "The natural world is changing, including the timing and numbers of birds on migration and a crucial challenge facing scientists is to identify and understand these changes and their causes.

It's too early to say for sure why some birds are arriving so much earlier on Fair Isle, while others seem to be delaying their arrival, but possible causes include changing climate and weather patterns, also changes in the summer breeding range and population size of many species across Europe."

Fair Isle is Britain's most remote inhabited island, lying between Shetland and Orkney. It is an internationally renowned hot-spot for bird migration and for over 60 years the Fair Isle Bird Observatory has made daily census counts of migrant birds. This written record was recently digitised, producing an extremely detailed and valuable dataset.

The Fair Isle Migration Project is a brand new initiative to analyse this dataset and uncover its secrets.

As well as changes in migration patterns it is revealing that the number of scarce migrant birds, arriving in Scotland from Eastern Europe and Siberia in the autumn, has risen sharply over the last 60 years, and is continuing to do so. Birds such as the yellow-browed warbler and the barred warbler have increased in number.

Dr Will Miles, a former assistant warden at the Observatory, will also talk about the ornithological year on Fair Isle, which has recorded more first sightings of rare birds than any other place in Britain.