Bird Migration Theory

Complete the notes. Write ONE WORD ONLY in each gap.

Bird Migration Theory

Most birds are believed to migrate seasonally.

Hibernation theory
  ● It was believed that birds hibernated underwater or buried themselves in 31.
  ● 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. and thought they then turned into robins.
   – Aristotle’s assumptions were logical because the two species of birds had a similar 33.

17th century
  ● Charles Morton popularised the idea that birds fly to the 34. in winter.

Scientific developments
  ● In 1822, a stork was killed in Germany which had an African spear in its 35.
   – Previously there had been no 36. that storks migrate to Africa
  ● Little was known about the 37. 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.
   – Ringing depended on what is called the 39. ‘’ of dead birds.
  ● In 1931, the first 40. to show the migration of European birds was printed.