Large flocks of birds start to migrate when the right time comes. It is not known what triggers this instinct but the biological clock inside their body is strongly set that they depart and arrive at the right place at the same date every year.
Birds prepare for their long trips by eating large amounts of food. This builds up fat which acts as a fuel for their flight. Some birds increase their body weight by as much as 50% to survive long flights. This is because they may even lose half or one quarter of their original weight. In order to replenish their energy, most of the birds prefer to travel at night and feed during daytime. During day, the migrants can see each other to keep together but at night they use call notes to keep in touch with each other. Travelling at night has yet another advantage – it reduces the amount of dehydration that would happen when they travel under the sun.
The traditional route through which they migrate is called flyway. A technique called biotelemetry is used by researchers in tracking animals or birds over short distances. Normally these birds do not get lost as they depend on the sun and the stars for orienting towards the right direction. Certain species are tuned in to the earth’s magnetic field, infra red rays or even changes in air pressure to orient them along the desired path.
Fog or continuous winds have the ability to deviate them from their original path. When the birds go off course and cannot find their original path, new territories get formed. How do animals realize the period and place for migration?