A major survey into bird migration from Africa over the past 60 years has revealed substantial changes in behaviour.
The Fair Isle bird observatory has recorded bird migration at its station between Shetland and Orkney since 1938.
A new initiative - the Fair Isle migration project - has now analysed records from the sanctuary since 1955.
The study has also revealed changes to the times of the year the birds are migrating.
The research has concluded spring migration has happened much earlier in recent years for many species, such as the swallow, which is arriving up to three weeks earlier than the birds did in the 1950s.
For other species, such as the willow warbler, spring migration has occurred much later.