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. Large birds, like geese and birds
of prey, usually migrate during
the day.
But smaller birds, like robins, migrate at
night.
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. 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. NORTH
An abundance of food in the summer. Little available food in
the winter.
Autumn
Spring
SOUTH
Available food all year round.
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.
9. 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).
