Migrating Birds may Actually 'See' North

Many migrating bird species need to determine north to accurately gauge their direction. But how do they do this? Do they look at the sun and analyze their position relative to it? Do they have a detailed neural map they follow? Do they really need subcutaneous magnetic crystalline structure laden beaks that help them find North? The answers to these questions are 'probably', 'maybe?' and 'uhhh…'.

New research has shown that migrating birds may actually see the magnetic field of the earth as a visual sensation. Molecules have been found in the birds’ eyes that are directly connected to the brain, allowing them to perceive north visually, and orient themselves correctly.

Migratory birds in Germany were injected with a tracer that can follow neuron firing pathways anywhere in the brain. The area of the brain chosen to trace was known ominously as CLUSTER N. They also injected a tracer into the retina of the bird. When these birds had a desire to migrate, the scientists would find where the tracers went. Interestingly, both retinal and neuronal fibre tracers ended up in the part of the thalamus responsible for vision.

“This anatomical link strongly supports the notion that the birds probably experience magnetic fields as a visual sensation”,

say scientists at the University of Oldenburg.

Previous attempts to solve the bird magnetic field phenomena revolved around ‘cryptochromes’, proteins in the birds eye that may play a role in their migratory compass. “These cryptochromes might be sensitive to the electronic state of radical pairs” say researchers, allowing the birds to look in a certain direction and percieve magnetic north as a dark spot in their plane of vision. But this research has been reduced to guesswork because scientists cannot truly tell what the bird is actually seeing.

So is this 'visualization of magnetism' now the definitive theory of migratory bird navigation? No more theories-of-gut-feelings or mutantbirdfreak ESP?
Not quite. While this connection between eye molecules and visual brain pathways is intriguing, until we ‘see experiments where the magnetic field is conclusively shown to change neuronal activity in the thalamus’, we cant think this theory proven, just strongly suggested. There is also evidence showing that birds have other ways of path finding (and yes, that magnetic crystal beak thing is one of them). They conclude suggesting that the crystal structures, visual perception of north and the cryptochromes all work in harmony to lead the bird home.

Nature.com
http://www.nature.com/news/2007/070924/full/070924-5.html
Sept 26, 2007

Posted by NJB(1)