The dodo was a ground nesting , flightless bird. An adult dodo could grow to a height of about a meter and weigh between 45-50 pounds. The natural habitat of this kind of bird lay in the forest of Mauritius. Seed  and fruits that were found in the forest were the main food of the dodo birds. As they could easily get the food they required in the forest, they didn't need to fly. As time went by, they finally lost the ability to fly. It turned out to be a major disadvantage for dodos, as they were left with no ability to protect themselves against human beings' attacks in their natural habitat, which drove this kind of bird to extinction . The extinction of the dodo started in 1505, when Portuguese sailors set their foot on the Island of Mauritius. Before this, the dodo didn't face any danger. People began to hunt them. It was not long before animals, like cats, pigs and monkeys, were also introduced to the island by humans. When ships arrived, the rats on these ships came onto the land. Though these animals were not able to attack huge dodos, it was easy for them to attack dodos' nests on the ground. These animals continued to feed on dodo eggs. The dodo became a relatively  rare bird in Mauritius at the beginning of the 17thcentury, and became extinct in the end. The last reported sighting of a dodo was in 1681. What does the passage mainly talk about?
The extinction of the dodo. The appearance of the dodo. The actions taken to protect the dodo. The punishment for hunting the dodo.