Từ điển các tính năng một bảng đầy đủ các nội dung và chỉ số để tham khảo dễ dàng, và minh họa đơn giản, dễ dàng để xác định, và dán nhãn rõ ràng. Oxford-Dudens nổi tiếng thế giới xuất sắc của họ, cuối cùng là một trong đó sẽ là một tài liệu tham khảo hữu ích chung cho tất cả người nói tiếng Anh. | Ont of the greatest mysteries of nature is the instinct to migrate. Every year millions of creatures feel the need to move for one reason or another Most of US have seen the arrival or departure of migrating flocks of birds. Migration however is not confined IO birds but cart be seen in reptiles for example turtles frogs insects butterflies locusts fish eels salmon runny and num-male reindeer seals lemmings whales bats . Many of these creatures succeed 111 navigating over Long distances. How exactly they manage to do this still remains a mystery There arc several possibilities. They may navigate by using one or more of the following 1 The sun. 2 The stars. 3 The Earth s magnetic field. When a small bar magnet is attached to a pigeon It IS unable to navigate. 4 A sense of smell. 5 Geographical features. Birds flying from Nonh Africa to France seem IO follow coastlines and valleys 6 Changes in temperature. Salmon can detect 3 change in water temperature .15 small as 0-03 c. 7 Sound. Whales and bats seem to use sonar. Experiments suggest that these navi- gational abilities are partly instinctive. Ill one fatuous experiment a young seabird from the island of Skokholm off the Welsh coast was taken across the Atlantic by plane to Boston 5100 km away It was re- Arctic region and one in the Antarctic. These regions have almost con- hand und was back ill its nest nd a half days later. This seabird holds the record for long-distance migration. Arctic Tern breed in Northern Canada Green- land Northern Europe Siberia and Alaska ill late August they set off on a 17 500 km journey which takes Them south past the Wesr coasts of Europe and Africa to the tip of Southern Africa 14 000 km in 90 days . They then fly round to the Indian MIGRATION Ocean and down to Antarctica where they spend the Antarctic summer. On the way back they sometimes make a complete circuit of Antarctica before returning to their breedinggrounds. The round trip is over 35 000 km in eight months 140 km a day .
