The homing pigeon's internal compass may lie in their liver, with its high concentration of iron. This is according to a recent study from the University of Bonn and the Max Planck Institute of Animal Behavior (MPIAB) in Germany. The study found that pigeons' macrophages, specialized white blood cells in the liver, possess a quantum property called superparamagnetism, which may act as a compass 'needle' in a surprisingly literal sense. The researchers also discovered nerve fibers capable of carrying signals from the macrophages all the way to the pigeon brain. This internal, quantum liver compass could be especially important on overcast days when the Sun is not a clear navigational marker. The study involved taking 34 homing pigeons on a test run, 19 kilometers from their home at MPIAB, to see how well they could find their way back under overcast conditions. A day before taking flight, 18 pigeons were given a shot of clodronate, a drug that wipes out macrophages, thereby destroying the connection between these immune cells in the pigeons' livers and the neurons that relay signals to the brain. The results showed that pigeons that hadn't been given clodronate arrived home within 70 minutes of release, while those who had been disconnected from their quantum liver compass were totally lost. However, once the weather cleared and the Sun shone again, the clodronate-treated pigeons homed normally. This suggests that the 'internal compass' in their liver may indeed be most important when there's no Sun to guide the way. The study's findings raise a deeper question about the role of immune cells in animal navigation. If immune cells are part of how birds sense direction, it would fundamentally change how we understand navigation. The research is published in Science and offers a fascinating insight into the natural world, highlighting the complexity and wonder of animal navigation.
