Every day birds are migrating around some portion of the globe. In March ruby-throated hummingbirds, 8.5 cm long and weighing some 5grams, wait for tail winds to aid their 18hour non-stop flight across the Gulf of Mexico. At roughly the same time, bar headed geese arrive honking at the foothills of the Himalayas, to fly over these formidable mountains on flight paths that can take them above Everest. In May, Swifts return to England from South Africa, their feet touching ground for the first time in 10 months.

Birds were migrating to continents thousands of years before European explorers ‘discovered’ them. Even as human civilisation began, it seems we have been watching their flight. Birds were painted on the walls of Egyptian tombs. The augurs of Rome looked to patterns of birds to determine the will of the gods. Centuries later the bible recorded ‘even the stork in the sky knows her appointed seasons, and the dove, the swift and the thrush observe the time of their migration’ (Job 39:26). The movements and comings and goings of birds have meant different things to different cultures. Yet today, many people remain unaware of these spectacular journeys.

The following pages introduce the what, why, when and how of migration. The information focuses on one of the main flyways birds use to cross the Mediterranean: the western flyway over the Strait of Gibraltar. This is part of the Palaearctic-African migration: a migration some 15,000 years old and still evolving.