# Bird Migration Theory: answers and explanations

Cambridge IELTS 17, Test 3, Listening Part 4

Source: Recording, questions and answer key from Cambridge IELTS 17, Test 3, Listening Part 4. © Cambridge University Press & Assessment. Used for educational practice. Explanations and evidence notes are written by Testmigo.

## Answer key

| Q | Answer | Proof |
| --- | --- | --- |
| 31 | mud | they spent winter hidden in mud |
| 32 | feathers | small birds called redstarts began to lose their feathers |
| 33 | shape | given that this pair of species are similar in shape |
| 34 | moon | Claiming that birds migrate to the moon and back every year. |
| 35 | neck | because of the long spear in its neck |
| 36 | evidence | Because it was the first evidence that storks spend their winters in sub-Saharan Africa. |
| 37 | destinations | very little information was available about the actual destinations of particular species |
| 38 | oceans | could fly over vast oceans |
| 39 | recovery | and relies upon what is known as recovery |
| 40 | atlas | an atlas was published showing where the most common species of European birds migrated to |

## Why these answers are right

**31. mud.** The note says birds were thought to hibernate underwater or bury themselves in ___. The lecturer describes a second theory that birds spent winter hidden in mud until food returned. Buried in and hidden in match, so mud is the answer.

**32. feathers.** Aristotle saw that in autumn redstarts began to lose their feathers and decided they were turning into robins. The note's experience the loss of ___ is a noun phrase version of lose their, so feathers is the answer.

**33. shape.** The lecturer says Aristotle's assumptions are understandable because the two species are similar in shape. Understandable becomes logical in the note, and similar in shape becomes a similar ___, so shape is the missing word.

The why and the trap for questions 34 onwards are free with an account on the [answers page](https://testmigo.com/ielts/listening/bird-migration-theory/answers).

## Transcript

**Announcer:** Part 4, you will hear a zoology student giving a presentation on bird migration.

**Announcer:** First, you have some time to look at questions 31 to 40.

**Announcer:** Now listen carefully and answer questions 31 to 40.

**Speaker:** Scientists believe that a majority of the Earth's bird population migrate in some fashion or other.

**Speaker:** Some travel seasonally for relatively short distances.

**Speaker:** Such as birds that move from their winter habitats in lowlands to mountaintops for the summers. Others, like the Arctic Tern, travel more than 25,000 miles seasonally.

**Speaker:** Between the northern and southern poles.

**Speaker:** Bird migration has been studied over many centuries through a variety of observations, but until relatively recently, where birds went to in the winter was considered something of a mystery.

**Speaker:** The lack of modern science and technology led to many theories that we now recognize as error filled, and even somewhat amusing.

**Speaker:** Take hibernation theory for example, 2000 years ago, it was commonly believed that when birds left an area, they went underwater to hibernate in the seas and oceans.

**Speaker:** Another theory for the regular appearance and disappearance of birds was that they spent winter hidden in mud, till the weather changed and food became abundant again.

**Speaker:** The theory that some birds hibernate persisted until experiments were done on caged birds in the 1940s which demonstrated that birds have no hibernation instinct.

**Speaker:** One of the earliest naturalists and philosophers from ancient Greece was Aristotle, who was the first writer to discuss the disappearance and reappearance of some bird species.

**Speaker:** At certain times of year, he developed the theory of transmutation, the seasonal change of one species into another, by observing redstarts and robins.

**Speaker:** He observed that in the autumn, small birds called redstarts began to lose their feathers, which convinced Aristotle that they changed into robins for the winter.

**Speaker:** And back into redstarts in the summer.

**Speaker:** These assumptions are understandable, given that this pair of species are similar in shape.

**Speaker:** But are a classic example of an incorrect interpretation based on correct observations.

**Speaker:** The most bizarre theory was put forward by an English amateur scientist, Charles Morton, in the 17th century.

**Speaker:** He wrote a surprisingly well regarded paper.

**Speaker:** Claiming that birds migrate to the moon and back every year.

**Speaker:** He came to this conclusion as the only logical explanation for the total disappearance of some species.

**Speaker:** One of the key moments in the development of migration theory came in 1822 when a white stork was shot in Germany.

**Speaker:** This particular stork made history because of the long spear in its neck, which incredibly had not killed it.

**Speaker:** Everyone immediately realized this spear was definitely not European.

**Speaker:** It turned out to be a spear from a tribe in central Africa.

**Speaker:** This was a truly defining moment in the history of ornithology.

**Speaker:** Because it was the first evidence that storks spend their winters in sub-Saharan Africa.

**Speaker:** You can still see the arrow stork in the zoological collection of the university of Rostock in Germany.

**Speaker:** People gradually became aware that European birds moved south in autumn and north in summer, but didn't know much about it until the practice of catching birds.

**Speaker:** And putting rings on their legs became established.

**Speaker:** Before this, very little information was available about the actual destinations of particular species.

**Speaker:** And how they traveled there.

**Speaker:** People speculated that larger birds provided a kind of taxi service for smaller birds by carrying them on their backs.

**Speaker:** This idea came about, because it seemed impossible that small birds weighing only a few grams could fly over vast oceans.

**Speaker:** This idea was supported by observations of bird behavior, such as the harassment of larger birds by smaller birds.

**Speaker:** The development of bird ringing, by a Danish school teacher, Hans Christian Cornelius Mortensen, made many discoveries possible.

**Speaker:** This is still common practice today, and relies upon what is known as recovery.

**Speaker:** This is when ringed birds are found dead in the place they have migrated to.

**Speaker:** And identified.

**Speaker:** Huge amounts of data were gathered in the early part of the 20th century, and for the first time in history, people understood where birds actually went to in winter.

**Speaker:** In 1931, an atlas was published showing where the most common species of European birds migrated to.

**Speaker:** More recent theories about bird migration...

**Announcer:** That is the end of part 4.

**Announcer:** You now have one minute to check your answers to part 4.

[Practice Bird Migration Theory](https://testmigo.com/ielts/listening/bird-migration-theory)