GREENERY: JOURNEYS IN THE SPRINGTIME

Spring moves north at roughly 30 miles a day - in other words, walking pace. Tim Dee follows swallows and other favourite birds from their wintering quarters in South Africa, through staging-places in Chad and Ethiopia, across the Sahara and into Europe. He meets people for whom spring is the determining season - a Sámi reindeer herder, an Egyptian taxi driver, a chronobiologist in arctic Norway. And on the shores of the Arctic Sea he finds swallows in midsummer - just at home there as they were in Cape Town in December.