Bird Migration

While all birds do not migrate, the often colorful appearances and melodic songs of the hundreds of migrant birds are a cause for local, national and international celebrations.

The topic of bird migration continues to fascinate both the professional ornithologist and the bird enthusiast. More specifically, people want to know how migrants consistently navigate such long distances?

A quick look at the major North American flyways suggests that geographical factors such as coastlines, mountain chains and rivers serve as large landmarks that are easy to follow.

Scientists also hypothesize that birds can recognize environmental clues such as the position of the sun in the sky to help with their navigation.

The most recent recent research also suggests that migratory birds posses an internal compass that can detect the earth's magnetic field, which keeps them moving north during the spring and south during the fall.

The following resources provide additional, in depth information about the topic.

The on line text Migration of Birds provides a great starting point for general information about North American bird migration.

Starting with historical anecdotes such as the belief that birds hibernated rather than migrated, the book takes the reader through the details of North American bird migration facts and patterns. The general information is supplemented with maps and details about migration patterns for specific bird species.

Much of what we known about bird migration comes from data collected by field observers. A 2009 report about New Technologies for Monitoring Bird Migration, improves on the field observation knowledge, saying,

"Bird tracking methods such as radio tracking, satellite tracking, geolocator loggers, passive integrated transponders or even the use of the worldwide mobile phone network for animal tracking are rapidly evolving and offer high spatial and temporal resolution for following bird movements. However, there are still limitations in equipment size and costs as well as in long-term data management which is still far from the highly standardised database system established for bird ringing data."

Two articles provide insight into current research regarding the physiological aspects of bird migration. Magnetic Orientation in Birds explains,

"A magnetic compass has been demonstrated in 18 species of migrating birds. In all species studied with regard to its functional properties, it was found to be an "inclination compass", i.e. the birds derive directional information from the inclination of the field lines, and thus distinguish between 'poleward' and 'equatorward' rather than 'north' and 'south'."

A follow up study, Magnetoreception and Its Use in Bird Navigation locates the compass mechanisms in both the beak and eyes.

"Recent advances have brought new insight into the physiological mechanisms that enable birds and other animals to use magnetic fields for orientation. Many birds seem to have two magnetodetection senses, one based on magnetite near the beak and one based on light-dependent radical-pair processes in the bird's eye(s)."

© 2010 Patricia A. Michaels