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MIGRATION
AND
NAVIGATION
MIGRATION
“In its purest sense, migration refers to
seasonal movements between a location
where an individual or population breeds
and a location where it survives during the
non breeding period.”
STIMULUS FOR MIGRATION
• Genetic clock and environmental factors influence
migration
• Photo period is an important migratory sign for many
birds
• Development of gonads
• Fat deposition
• It is believed that anterior lob of pituitary gland and
pineal body are involved in photoperiod responses.
LONG-DISTANCE MIGRATION:
Long-distance migrants are those that
have a complete shift between the breeding
and wintering areas, such as the Blackpoll
Warbler.
For example:
swallows and birds of prey making long flights to the
tropics. Many northern-breeding ducks, geese and
swans are also long-distance migrants, but need only
to move from their Arctic breeding grounds far
enough south to escape frozen waters.
Swallow
Swans
Ducks
SEABIRD
MIGRATION:
Most Terns and Auks breeding in the
temperate northern hemisphere, move
varying distances south in winter. The Arctic
Tern has the longest-distance migration of
any bird, and sees more daylight than any
other, moving from its Arctic breeding
grounds to the Antarctic non-breeding areas.
Seabirds have the additional advantage of
being able to feed during migration over
open waters.
Arctic Terns
Terns
AUKS
Many of the smaller insectivorous birds including the warblers,
hummingbirds and flycatchers migrate large distances, usually at
night. They land in the morning and may feed for a few days before
resuming their migration.
The birds are referred to as passage migrants in the regions where
they occur for short durations between the origin and destination.
By migrating at night, nocturnal migrants minimize
predation, and avoid overheating that could result from the energy
expended to fly such long distances. This also enables them to feed
during the day and refuel for the night
Warbler
( Perching bird )
Short-Distance Migration:
Short-distance migrants,
such as the Pine Warbler, make shorter
trips, such as up and down the side of a
mountain.
Many species move shorter
distances, but may do so only in response to
harsh weather conditions. Thus mountain and
moorland breeders, such as Wall creeper and
White-throated Dipper, may move only
attitudinally to escape the cold higher ground.
Wall creeper
White-throated Dipper
PARTIAL MIGRATION:
Partial migrants are those species
in which some individuals of a species leave and
others stay, such migration is called partial
migration,e.g American Robins. Average distances
covered are about 1000-3000 km each way .
LEAP-FROG MIGRATION:
In some species the population at higher
latitudes tend to be migratory and will often winter at
lower latitude past the latitudes where other populations
may be sedentary, with suitable wintering habitats
already occupied, and this is termed as leap-frog
migration.
FOOD HABITS AND MIGRATION:
There is often a relationship between food
habits and migration. Insects become scarce in the winter in
northern latitudes, so insectivorous birds must move closer to
the equator where insects are more abundant. Insectivorous
birds are the largest group of migrants.
Fruit-eating birds may not have to migrate
as far because fruits are generally available at the edge of the
temperate zone.
Fish-eating birds may be cut off from their
food supply when northern lakes freeze.
Large hawks which feed on mammals and
birds tend to migrate because their prey either hibernates or
migrates. In addition, photoperiod shortens and they have
less time for hunting.
NAVIGATION
How does a bird find its way? We can learn some
things about the navigation and orientation
behavior of birds through observation but the best
information has come through experiments.
TYPES OF NAVIGATION:-
•Rout based navigation
•Location based navigation
ROUT BASED NAVIGATION:It involves the following track of
land marks during their outward
journey
LOCATION BASED NAVIGATION
In this case direction
of the destination is followed from the
information available at site of start of
the journey. It involves the use of sun
compasses and other celestial cues.
the magnetic field of the earth is also
followed.
Sun compass:The lenses of the birds are
transparent for ultraviolet light. Their
photoreceptors respond to ultraviolet
radiations.
Thus they orient themselves according
to the position of sun this orientation
sign is called a sun compass.
The sun move b/w sun rise and sunset.
Birds use internal clocks to sense the sun
rises in the east. The sun is overhead at
noon. It sets in west.
The biological clocks of migratory birds can
be changed. In an experiment birds ready
for northward migration is held in
laboratory. The laboratory sun rise occur
later than the natural sun rise. After that
they are released to natural light
conditions.
They fly in a direction they sense to be
north. But it is nearly northwest. Night
migratory birds can also use sun. They fly
in proper direction from the sun set.
CELESTIAL CUES:Celestial cues other than the sun are also
used for navigation. The north star lines up
with the axis of rotation of earth in the
northern hemisphere. The angle b/w the
north star and the horizon decreases as we
move towards the equator. The latitudes of
earth can be determined by this method.
Birds also use similar paten to determine
latitude.
Magnetic compass:Birds use magnetic compasses to detect
the magnetic field of earth. The determine
their direction from this magnetic field. If
the magnets are strapped with the heads
of pigeons, it disorient the birds. e.g.
European robin and the garden warbler use
the earth’s magnetic field for orientation.
But magnetic receptors are not found in
any of the birds.
There were early report that magnetic
irons and magnetite are present in the
head and necks of pigeons.
some zoologist believes that the pineal
body of pigeons use the sun compass in
response to magnetic field.
THE END
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