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Bird migration (Ǩáã)
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(³Á»ý). 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(ʳÈ⶯Îï), 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 (´Å³¡), 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(ºòÄñ) 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(·±Ö³)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.
Bird migration | |
Passage outline | Supporting details |
Why do birds migrate? | Besides1._____, migration has something to do with birds¡¯ physical changes and day length changes. |
What are the advantages of night migrating? | ¡óNight migrating helps minimize the 2._______ of being threatened by predators. ¡óNight migrating allows birds to feed enough during the day with out overheating. |
3.______do birds migrate? | ¡óThe sun, magnetic field, visual landmarks and the sense of smell are all 4.____for birds to migrate. ¡óEnvironmental changes are connected with birds¡¯ timing and route. ¡óNot only magnetic field but also some other capabilities and 5._____ relate to a first-timer migrant¡¯s flying. |
Where do birds migrate? | ¡óMigration mainly takes place in the 6._____ Hemisphere. ¡óWith four major flyways birds mainly fly 7.______ coasts, rivers, or mountain ranges. |
What 8.________ can you draw from the bird migration? | ¡óBirds are 9._______ to their site attachment very much. ¡óYou must make sure the clean boxes are 10.______ before the birds come back. |
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