Bird Migration

We know more about bird migration than other animal migrations. Because bird species vary in the details of their migratory mechanisms, an in-depth analysis of migratory mechanisms in birds would be quite complicated. Fortunately, the basic mechanisms are the same in all birds, so a generalized picture of bird migration is easy to construct.

Information about migratory direction is innate (genetically coded)

Supporting data for this assertion comes from displacement experiments, in which birds are captured and transported some distance from their normal point of departure for migration. Displaced birds maintain the migratory direction of their parental stock. Juvenile starlings, for example, displaced 800 kilometers moved in parallel to the the flock they came from, in a southwesterly direction. (Interestingly, adult starlings benefited from experience and compensated for the displacement by modifying their flight path.)

Another experimental approach is to hand-rear birds and then record their flight directions in laboratory cages designed to stimulate migratory-like flights. These experiments show that birds fly in the direction predicted by the behavior of their parents' migratory patterns, even though they have never had contact with them.

Information about migratory distance is also innate

Time and or metabolic effort is monitored and birds stop their migration at an appropriate location based on these measures. As with the directional information, experience may allow birds to incorporate other cues, such as odor (see the page on homing by pigeons) or landmarks to supplement or calibrate the innate information. For birds that migrate in flocks, following other birds (observational learning) may also be an important factor.

Compass information is gained from celestial sources and is calibrated by geomagnetic inputs

Even though directional information may be innate, birds need to align their path with an external compass. Day-migrating birds usually employ a sun-compass or polarized light patterns in the daylit sky, night-migrating birds rely on a star-compass. Sunset cues (the point on the horizon at which sun disappears) can provide important information as well.

Sandberg R, Backman J, Moore F R, Lohmus M. 2000. Magnetic information calibrates celestial cues during migration Animal Behaviour 60: 453-462
Mouritsen H 1998 Redstarts, Phoenicurus phoenicurus, can orient in a true zero magnetic field Animal Behaviour 55: 1311-1324
Weindler P, Bohme F, Liepa V, Wiltschko W 1998 The role of daytime cues in the development of magnetic orientation in a night-migrating bird Behavioral Ecology And Sociobiology 42: (4) 289-294
Weindler P, Liepa V, Wiltschko W 1998 The direction of celestial rotation affects the development of migratory orientation in pied flycatchers, Ficedula hypoleuca Ethology 104: (11) 905-915
Wiltschko W, Weindler P, Wiltschko R. 1998. Interaction of magnetic and celestial cues in the migratory orientation of passerines Journal Of Avian Biology 29: (4) 606-617