Pigeons May Have a Magnetic Compass Hidden in Their Livers

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A new study suggests that homing pigeons may have an unexpected navigation tool hidden in their livers. Researchers found that iron-rich immune cells called macrophages have superparamagnetic properties and may help the birds sense Earth’s magnetic field. The idea matters because scientists have known for decades that pigeons can use magnetic information to help find their way, but the exact biological mechanism has remained debated. Earlier theories have focused on structures in the beak, light-sensitive systems in the eyes, and other possible sensors. In the new research, scientists examined several pigeon tissues and found the strongest magnetic response in the liver, where macrophages naturally collect iron while breaking down old red blood cells. The researchers then tested whether these cells actually mattered for navigation. Pigeons were trained to return home from about 19 kilometers away. When their liver macrophages were temporarily depleted, the birds lost their normal directional ability during completely overcast conditions. When sunlight was available, the birds could still navigate, suggesting that solar cues remained an effective backup. The researchers propose that groups of these iron-rich macrophages could detect changes in Earth’s magnetic field and send information toward the brain through nearby nerve pathways. The finding does not mean the entire mystery of animal magnetoreception is solved. Exactly how the magnetic signal is converted into information the brain can use remains an open question, and other proposed magnetic-sensing mechanisms are still being investigated. Still, the work points to a surprising connection between the immune system and animal navigation.