1One of the most famous cases of extinction is that of a bird known as the dodo.
2In fact there's even a saying in English, 'as dead as the dodo',
3used to refer to something which no longer exists.
4But for many centuries the dodo was alive and well,
5although it could only be found in one place,
6the island of Mauritius in the Indian Ocean.
7It was a very large bird, about one metre tall,
8and over the centuries it had lost the ability to fly,
9but it survived happily under the trees that covered the island.
10Then in the year 1507,
11the first Portuguese ships stopped at the island.
12The sailors were carrying spices back to Europe,
13and found the island a convenient stopping place
14where they could stock up with food and water for the rest of the voyage,
15but they didn't settle on Mauritius.
16However, in 1638
17the Dutch arrived and set up a colony there.
18These first human inhabitants of the island
19found the dodo birds a convenient source of meat,
20although not everyone liked the taste.
21It's hard to get an accurate description of what the dodo actually looked like.
22We do have some written records from sailors,
23and a few pictures,
24but we don't know how reliable these are.
25The best-known picture is a Dutch painting,
26in which the bird appears to be extremely fat,
27but this may not be accurate -
28an Indian painting done at the same time shows a much thinner bird.
29Although attempts were made to preserve the bodies of some of the birds,
30no complete specimen survives.
31In the early 17th century
32four dried parts of a bird were known to exist -
33of these, three have disappeared,
34so only one example of soft tissue from the dodo survives,
35a dodo head.
36Bones have also been found,
37but there's only one complete skeleton in existence.
38This single dodo skeleton has recently been the subject of scientific research
39which suggests that many of the earlier beliefs about dodos
40may have been incorrect.
41For example,
42early accounts of the birds mention how slow and clumsy it was,
43but scientists now believe
44the bird's strong knee joints would have made it capable of movement which was not slow,
45but actually quite fast.
46In fact, one 17th century sailor wrote that he found the birds hard to catch.
47It's true that the dodo's small wings wouldn't have allowed it to leave the ground,
48but the scientists suggest that these were probably employed for balance
49while going over uneven ground.
50Another group of scientists carried out analysis of the dodo's skull.
51They found that the reports of the lack of intelligence of the dodo
52were not borne out by their research,
53which suggested the bird's brain was not small,
54but average in size.
55In fact, in relation to its body size,
56it was similar to that of the pigeon,
57which is known to be a highly intelligent bird.
58The researchers also found that the structure of the bird's skull
59suggested that one sense which was particularly well-developed was that of smell.
60So the dodo may also have been particularly good at locating ripe fruit
61and other food in the island's thick vegetation.
62So it looks as if the dodo was better able to survive and defend itself than was originally believed.
63Yet less than 200 years after Europeans first arrived on the island,
64they had become extinct.
65So what was the reason for this?
66For a long time, it was believed that the dodos were hunted to extinction,
67but scientists now believe the situation was more complicated than this.
68Another factor may have been the new species brought to the island by the sailors.
69These included dogs, which would have been a threat to the dodos,
70and also monkeys,
71which ate the fruit that was the main part of the dodos' diet.
72These were brought to the island deliberately,
73but the ships also brought another type of creature - rats,
74which came to land from the ships and rapidly overran the island.
75These upset the ecology of the island,
76not just the dodos but other species too.
77However,
78they were a particular danger to the dodos
79because they consumed their eggs,
80and since each dodo only laid one at a time,
81this probably had a devastating effect on populations.
82However,
83we now think that probably the main cause of the birds' extinction
84was not the introduction of non-native species,
85but the introduction of agriculture.
86This meant that the forest that had once covered all the island,
87and that had provided a perfect home for the dodo,
88was cut down so that crops such as sugar could be grown.
89So although the dodo had survived for thousands of years,
90suddenly it was gone.