Birdmigration(迁徙)Themanreasonformigrationormovementisfo...

问题详情：

Bird migration (迁徙)

The man reason for migration or movement is food; for example, some birds may choose not to migrate if they are fed through the cold months Changes in the day length are signals for migration and relate to the physical changes in the birds. Birds will also display restlessness and increase their fat deposition(沉积). During shorter days in the fall, birds will return to warmer areas where they find adequate food supply.

Many smaller insect-eating birds migrate large distances usually at night. They may feed for a new days before continuing their course of travel. An advantage for night migrating is that it minimizes the threat of predators(食肉动物), allowing the birds to feed during the day and avoid overheating.

The migration for these birds is based on a number of different senses. Many birds use the sun as a compass. The ability to detect magnetic field (磁场), use of visual landmarks, as well as their sense of smell are used to help travel during migration. Bird migration is a strong genetic factor in terms of timing and route, which can be influenced by temperature. Migratory birds may use two tools to find their destinations; innate capability(genetically programmed) and experience. A first-timer migrant(候鸟) flies according to the Earth’s magnetic field, but does not know how far it will take until it grows accustomed to the journey and is able to use its other capabilities. With experience it learns various landmarks often called “mapping”.

Migration is mainly seen in the Northern Hemisphere and less obvious in the Southern Hemisphere. This is due to the lack of significant weather changes and the continual supply of food for the birds. A common pattern in migration involves flying north in the spring to bread(繁殖)during the summer and traveling to the south in the fall into warmer regions. No two species follow the exact route from beginning to end. Migrations narrow into one or more preferred routes or often called “flyways”. Flyways mainly follow coasts, sometimes rives, or mountain ranges. There are four major North American flyways; the Atlantic, the Mississippi, the Central and the Pacific Flyways. The flyways are not defined in their boundaries and at times may be combined into one.

In fact, long distance migrants move away from each other as young birds and form attachments to potential breeding and wintering sites. Once the site attachment is made, birds show high site-faith, visiting the same sites year after year. You will want to ensure your nesting boxes are cleaned out and available when these birds return to keep the cycle going for these migrating species.

【回答】

61．food

62．possibility/chance

63．How

64．helpful

65．experience

66．Northern

67．following/along

68．conclusion

69．faithful

70．available/ready

知识点：阅读填空

题型：阅读填空