Migration Navigation
How do birds navigate during migration?
Theory One: Birds' Brains Contain Magnetite (a.ka. iron oxide)
Magnetite in their bodies allows them sense magnetic fields and this allows them to detect north and south
Evidence:
-Magnetite has been found in the olfactory cavity of homing pigeons
-In studies homing pigeons change positions when magnetic fields become abnormal
However: This could be specific to homing pigeons
Bar-tailed Godwit Bar-tailed Godwit's Migratory Paths
Theory Two: Radical-pair Mechanism
Atlantic Puffin (migratory)
A molecule with an unpaired electron, otherwise known as a free radical, meets up with another free radical whose unpaired electron is spinning in the same direction as the first. The two free radicals will only combine when one of the electrons starts spinning in the other direction. However, magnetic fields of any strength make this difficult. Birds detect magnetic fields by sensing how difficult it is for the free radicals in their body to combine.
*Key fact: free radicals react to weak magnetic fields, magnetite requires a stronger magnetic field.*
Evidence:
-Birds exposed to weak magnetic fields began to fly in all directions; only flew north when simulated magnetic field lined up with Earths natural magnetic field
Canadian Goose (migratory) Indigo Bunting (migratory)
Theory Three: Cryptochromes in Bird’s Eyes (tied to Radical-pair mechanism)
Arctic Tern Chick (Arctic Terns undergo one of the longest migrations)
Cryptochromes, normally found in plants, create free radicals when exposed to ultraviolet light. The changing daylight hours of migratory season emit different levels of ultraviolet light than normal. The cryptochromes in the birds’ eyes react to this, tell the bird it is time to migrate, and then are used to detect magnetic fields while the bird is in flight.
Evidence:
-Cryptochromes have been found in the eyes of several
species of migratory birds
-Under normal conditions birds turn their heads from side to side a few times before taking off. In abnormal magnetic fields, they turn their necks many more times before taking off. (Bird moving head to detect magnetic fields with its eyes)
-Cryptochromes have been found connected to neurons sensitive to magnetism
Arctic Tern Canadian Goslings!