In A Wild Goose Chase, the final part of Animal Migration in a Climate of Change the focus is on wild geese.
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Wild geese make some of the most arduous journeys of any animal.
They winter around the estuaries and mudflats of north-west Europe and travel to some of the remotest Arctic territories to rear their young under the midnight sun.
Brett Westwood follows individual Greenland White-fronted geese, carrying special transmitters on their migration from south-west Scotland to the east coast of Greenland where they breed.
En route he catches up with them on their staging grounds in the west of Iceland where they feed to build up fat for the journey, before they cross the 3000m high Greenland ice-cap.
Using the latest telemetry technology, scientists from the Wildlfowl and Wetlands Trust can track the exact routes of the individual geese and even estimate their energy usage.
But for the Greenland White-fronts, there's a bitter twist in the tail.
When they arrive in western Greenland, their territories are being taken by Canada geese which are successfully colonising the country. Could climate change be the culprit?
First broadcast on October 8 2008.