Complete the notes below.

Write ONE WORD ONLY for each answer.

Bird Migration Theory

Most birds are believed to migrate seasonally.

Hibernation theory

It was believed that birds hibernated underwater or buried themselves in 31. [blank_1] .
This theory was later disproved by experiments on caged birds.

Transmutation theory

Aristotle believed birds changed from one species into another in summer and winter.

– In autumn he observed that redstarts experience the loss of 32. [blank_2] and thought they then turned into robins.

– Aristotle’s assumptions were logical because the two species of birds had a similar 33. [blank_3] .

17th century

Charles Morton popularised the idea that birds fly to the 34. [blank_4] in winter.

Scientific developments

In 1822, a stork was killed in Germany which had an African spear in its 35. [blank_5] .

– previously there had been no 36. [blank_6] that storks migrate to Africa

Little was known about the 37. [blank_7] and journeys of migrating birds until the practice of ringing was established.

– It was thought large birds carried small birds on some journeys because they were considered incapable of travelling across huge 38. [blank_8] .

– Ringing depended on what is called the 39.' [blank_9] ’ of dead birds.

In 1931, the first 40. [blank_10] to show the migration of European birds was printed.