Migration & Navigation of Birds

Man has wondered about the migration of birds ever since he made the simple discovery that many birds were present one day and gone the next, and that they returned many months later just as mysteriously as they disappeared. Migration is among the most remarkable of the phenomena related with bird life. The word migration is derived from the Latin word migra which means going from one place to another. Migration may also be defined as the periodic movement of animals to avail the favourable conditions obtaining in any part of the world. In birds, migration means a two way journey, journey from the original place or home to new places and a return journey homeward. It was not until almost the beginning of the 20^th century that migration began to be studied intensively and scientifically.

Kinds of Migration

1. Latitudinal: The most familiar periodic migration is from north to south or latitudinal. Usually birds migrate from their northern home to the south to pass the winter there and with the advent of summer, again migrate to the north. Migration of this kind is also found in the Southern hemisphere to a lesser extent and in opposite direction, since the seasons are reversed there.

2. Altitudinal: Some bird exhibit altitudinal or vertical migration, that is, they go to the mountainous regions in summer and return to the plains in winter. Juncos, Jays, Chikadees, etc., are birds of western United States which exhibit such altitudinal migration with changing seasons.

3. Longitudinal: Such migrations take place in the east-west direction. Red head ducks, evening grosbeaks and Californian gulls provide examples of this type of migration where the birds move to new places during winter.

4. Vagrant or irregular migration: Such migration is irregular and random. Some birds, like herons, gulls, terns, etc., disperse for a short or long distance in search of food and safety. In summer, young birds disperse in all directions from their birth place.

5. Partial migration: When some individuals of a species migrate while others stay on at their breeding places, it is called migration. Robins of England and thrushes are partial migrant birds. Some species of ‘passerine’ and shore birds also exhibit such partial migration.

6. Nocturnal: Such birds fly by night, while feed and rest during the day. Mainly smaller birds such as sparrows, thrushes and warblers, etc., are such night-fliers. They get protection from their enemies in the dark while flying.

7. Diurnal: Large birds, like pelicans, hawks, pigeons, swifts, swallow, etc., are day-fliers. They stop for feeding at suitable places.

It is quite interesting to know that there are some birds, like geese and ducks fly both by night and day while migrating.

Problem of Navigation (Way Finding)

The mystery as to how birds migrate to definite places in the north or south following the same routes with much regularity and accuracy has given rise to various theories and explanations,

1. Various landmarks like river valleys, mountain ranges, coastline, etc., are utilized by birds to guide them.

2. H L Yeglev suggested that birds are guided by terrestrial magnetism.

3. Migration has been explained as an instinctive behaviour, the instinct having developed as a cumulative inheritance of experience.

4. Gustav Kramoner, a German ornithologist, experimented with caged European starlings and proved that birds use the sun as compass to find out the direction during migratory flight.

5. Franz Saurer (Germany) experimented with warblers and concluded that night-fliers guide themselves with the help of stars during flight by night.