Donal Hickey: On a wing and a prayer

How do millions of birds travel thousands of kilometres and make a return trip to the same nesting site each year? Maybe they have some sort of hidden satnav that humans know nothing about or some other mysterious means of guiding them across oceans, writes Donal Hickey

There was once a common belief that migrating birds hitched lifts on ships which enabled them to get 5,000km across the Atlantic from North America to Ireland. The theory did not stand up to scrutiny. Nobody, for instance, could explain why the wanderers only arrived in migration seasons.