There have been some interesting developments in learning how birds navigate. It was thought that birds had tiny chunks of metal in their beaks or inner ears that enabled them to detect the direction of the Earth’s magnetic field. But more research has thrown doubt on the existence of these so-called ‘compass cells’, saying that they were just a type of white blood cells.
Every neuron had its own characteristic response to the magnetic field, with each giving a sort of 3-D compass reading along the familiar north-south directions as well as pointing directly upward or downward.
In life, this could help the bird determine not only its heading just as a compass does, but would also reveal its approximate position.
Each cell also showed a sensitivity to field strength, with the maximum sensitivity corresponding to the strength of the Earth’s natural field.
And just like a compass, the neurons had opposite responses to different field “polarity” – the magnetic north and south of a field, which surprised the researchers most of all.
There’s more about this here.