General overview

• Most bird species are thought to make seasonal journeys.

Hibernation theory

• An early explanation said birds spent winter below water or concealed in 1. .

• Experiments with captive birds eventually disproved this idea.

Transmutation theory

• Aristotle argued that birds became a different species according to the season.

• In autumn, he noticed redstarts shedding their 2.  and concluded that they became robins.
• His reasoning seemed plausible because the two birds were alike in 3. .

17th century

• Charles Morton spread the theory that birds travelled to the 4.  during winter.

Scientific developments

• In 1822, a stork was shot in Germany carrying an African spear in its 5. .
• Before this, there had been no 6.  that storks flew to Africa.
• Until ringing began, researchers knew little about migrating birds' 7.  or the routes they took.
• Some believed big birds transported smaller ones because the latter were thought unable to cross enormous 8. .
• Ringing relied on the '9. ' of dead birds.
• The first 10.  mapping the movements of European birds appeared in 1931.