The following is the abstract I wrote for my senior capstone project which was a PowerPoint Presentation I shared at Cedarville University:
The Role of Magnetoreception in Avian Migration
Jeffrey Doub
20 March 2006
Ornithologists have studied the methods of orientation and navigation that birds use in migration for over 50 years. Researchers first discovered evidence for the celestial and sun compass in the 1950s. When the use of the magnetic field was first suggested in 1947, scientists were very skeptical of the idea. By the late 1960s though, orientation experiments confirmed that birds orient using the Earth’s magnetic field. The magnetic field provides a global source of reliable information for birds to depend on during migration. This seminar will explain how two proposed mechanisms of magnetoreception function on a macroscopic and microscopic level and how birds use the information obtained for orientation and navigation. The priority of magnetic cues in relation to celestial cues will also be examined.
Birds can detect the inclination of the magnetic field, rather than the polarity. Orientation experiments indicate that birds scan with their heads to detect field inclination with a receptor located in the right eye. Scientists have proposed the involvement of a light-dependent radical pair reaction in this mechanism. In this model, the receptor is positioned in a fixed orientation perpendicular to the retina, producing varying product yields based on the alignment with the magnetic field. Studies using monochromatic light suggest the involvement of two receptors activated by different colors of light.
As a second mechanism of magnetoreception, birds can detect intensity differences in the magnetic field. Intensity may serve as a “map” mechanism to indicate position. Researchers have suggested the involvement of magnetite particles in detecting intensity. They have found single domain particles in the orbital and nasal cavity of birds. In addition, they have discovered clusters of magnetite crystals in nervous tissue in the upper beak of pigeons, associated with groups of iron platelets. Experiments using a pulse designed to change the magnetization of magnetite particles suggest that the particles are superparamagnetic.
Ornithologists have also studied the importance of magnetic cues in relation to celestial cues. Cue-conflict experiments have shown that during the premigratory period, celestial cues dominate, and serve to calibrate magnetic cues. In contrast, most studies performed during migration demonstrate the dominance of magnetic cues. However, a recent reanalysis of past cue-conflict experiments by Muheim and colleagues indicates that the magnetic field tends to dominate over other cues only when the birds are tested in orientation cages which block view of the sky near the horizon. Their review article discusses the possibility that celestial cues near the horizon, especially polarized light at sunset, may provide a single reference of calibration which dominates over all cues regardless of the time of season.
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