A research project has been set up to map the behaviour of Bewick swans now arriving at Slimbridge Wildfowl Centre in Gloucestershire.
The swans head to Slimbridge for winter each year
Each year the swans fly from Siberia but this time scientists at the Wildfowl and Wetlands Trust are taking an even closer interest.
When the swans are late - even slightly - the scientists want to know why.
A tiny transmitter has been attached to some of the swans enabling researchers to eavesdrop.
Of the 7,000 that set off every year about 400 go to Slimbridge.
Their journey is a flight of just under 2,500 miles.
More than 9,000 of the swans have been recorded at the centre in the past 38 years.
Each is recognisable by its individual bill pattern and is named by staff as part of continuing research into the birds' behaviour.
The work is designed to improve the swans chances of survival and also provide valuable pointers towards ecological change