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Reasons and Patterns of Migration


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Reasons and Patterns of Migration

  2. 2. The Migration of birds •Migration is the yearly, seasonal journey undertaken by many species of birds. During this journey, birds cover distances of many kilometres. •The most common types of migration are those carried out by birds in the spring and the autumn. In the autumn, they travel from breeding grounds in the north to wintering grounds in the south, and vice versa in the spring.
  3. 3. Large birds, like geese and birds of prey, usually migrate during the day. But smaller birds, like robins, migrate at night.
  4. 4. Birds depend on the amount of available food in an area to survive and raise their chicks, so when there is a shortage of food in one area, they move to areas where more food is available. Changes in the amount of available food in certain areas are related to changes in temperature. These changes occur in different seasons in different regions of the world.
  5. 5. STIMILUS FOR MIGRATION North Higher Latitudes About mid July gonads begin to regress, old feathers moult, fat accumulation starts , shorter days cause an urge to move southward in mid September. External Factor Variation in day length Internal factor Energy balance and physiological state of gonads South Lower Latitudes Increase in light duration in spring (March), less energy is utilized in temperature regulation, more becomes available for gonad activity. Activated gonads through hormones , produce an urge to move northward for breeding.
  6. 6. NORTH An abundance of food in the summer. Little available food in the winter. Autumn Spring SOUTH Available food all year round.
  7. 7. Migration Routes Well established routes • Land marks: Rivers, coastlines and mountain ranges • Directly over sea surface • Routes of two species rarely coincide • Certain species with different upward and backward routes • Wide or narrow migration lanes (Sandpipers) closer to coastline for feeding •
  8. 8. Birds that migrate from Northern Europe to regions in the south of the continent in the winter are called wintering or pre-Saharan birds (as they do not cross the Sahara). Birds that migrate from Africa to Europe to breed in the summer are called summering or trans-Saharan birds (as they cross the Sahara).