After 27 years, Melvyn Bragg has decided to step down from the In Our Time presenter’s chair. With over a thousand episodes to choose from, he has selected just six that capture the huge range and depth of the subjects he and his experts have tackled. In this fourth of his choices, we hear Melvyn Bragg and his guests discuss bird migration.

Their topic includes why some birds migrate and others do not, how they select their destinations and how they navigate the great distances, often over oceans. For millennia, humans set their calendars to birds' annual arrivals, and speculated about what happened when they departed, perhaps moving deep under water, or turning into fish or shellfish, or hibernating while clinging to trees upside down. Ideas about migration developed in C19th when, in Germany, a stork was noticed with an African spear in its neck, indicating where it had been over the winter and how far it had flown. Today there are many ideas about how birds use their senses of sight and smell, and magnetic fields, to find their way, and about why and how birds choose their destinations and many questions. Why do some scatter and some flock together, how much is instinctive and how much is learned, and how far do the benefits the migrating birds gain outweigh the risks they face?

With

Barbara Helm

Tim Guilford

and

Richard Holland

Producer: Simon Tillotson

Spanning history, religion, culture, science and philosophy, In Our Time from BBC Radio 4 is essential listening for the intellectually curious. In each episode, host Melvyn Bragg and expert guests explore the characters, events and discoveries that have shaped our world