Reed warblers are night migrants, known for their incredible instinct which allows them to calculate their east-west position during the breeding season. Even in the case of displacement, these songbirds have the ability to correct their orientation. Previous research has revealed that a tiny magnetic compass is possessed by the songbirds in each eye. However, this information is not enough to explain which sensory mechanisms and cues warblers use in determining longitude. Fortunately, a key to solving this phenomena lies in a second magnetic sense, involving the ophthalmic branch of the trigeminal nerve (V1). It is speculated that V1 channels magnetic information into the brain, which has lead researchers at the University of Oldenburg to a strong hypothesis in which V1 may serve as a magnetic map and is necessary in determining a reed warbler’s east-west position.
The methods in this double blind experiment included capturing 57 Eurasian reed warblers in Rybachy and separating them into groups. Some underwent a procedure involving the severing of V1 while the other birds participated in a sham surgery. The songbirds were then displaced 1,000km eastward in Zvenigorod, and their orientation was compared before displacement in Rybachy.
The results revealed that sham sectioned bird’s orientation shifted by 49 degrees counterclockwise compared to non operated birds in Rybachy, though they did in fact correct for displacement. The V1 sectioned birds however, did not adjust for the displacement. Their orientation was considerably different in comparison. Based on these results, it was evident that V1 plays an important role in detecting longitude in the magnetic field and therefore a reed warblers sensory ability to provide map related information. This information has lead researchers closer to determining the biological function of V1 including the possibility of transmitting information through magnetoreceptors and olfactory receptors.
These implications match with the evidence that was found from this study. However, there are quite a few restrictions with this study. For example, these results cannot be applied to all birds. Migratory homing pigeons are still able to navigate despite sectioning the V1 nerve, contradictory to the results from this study with reed warblers. Thus, navigational ability involving V1 may be species dependant. In addition to this, other research involving V1 in birds is virtually useless to compare this experiment to, due to the fact that many have not been able to be replicated, resulting in a very low reliability factor. Without this, it becomes increasingly harder to find out more about the function of this nerve in birds. In addition, there may be other cues which help songbirds to correct their displacement, for example: smell.
Thankfully, unknowns and complications from this experiment like the one mentioned above serve to be quite helpful because they can always be experimented with. The possibility of olfactory senses being a major contributing factor in bird migration can be tested to determine if transmitting odor is a function of V1. Therefore one can observe whether it has impact during bird migration. Most research isn’t perfect, so these kinks in studies provide a layout for future research to take place because there is always information to be found.