NAVIGATION

MIGRATION

AND

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:

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.

For example:

Long-distance migrants are those that have a complete shift between the breeding and wintering areas, such as the Blackpoll Warbler.

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

TernsAUKS

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.

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.

NAVIGATIONHow 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

Presented by:-

AMAAN ALI