Researchers examining bird brains have discovered that those who migrate large distances have more new neurons in brain regions involved in navigation and spatial orientation tasks. The findings, published in Scientific Reports, suggest that the regular activities of animals (including us) may determine how our brains adapt.
Neurons are generated in the brains of animals throughout their lifetime. These new neurons are created in one part of the brain and then recruited to areas where they’re needed the most. Researchers think that this neuronal recruitment in adult brains helps with what’s called brain plasticity, increasing the animal’s ability to deal with new challenges and changing environments. In addition to the physiological effort needed to travel vast distances, migratory birds must also avoid predators, minimize competition, and overcome bad weather – all while accurately navigating and orienting.
A team led by Shay Barkan of Tel-Aviv University studied the neurons of turtle doves (Streptopelia turtur) and reed warblers (Acrocephalus scirpaceus) who fly from Africa to the Middle East or Europe. Using mist nets, the team caught six reed warblers and 12 turtle doves in the Jordan Rift Valley during the spring and summer between 2005 and 2009. The birds were injected with a neuronal birth marker, and five weeks later, they were inspected for new neurons in brain regions known to play a role in navigation: the hippocampal complex and the nidopallium caudolateral.
The team also calculated the migration distance of each individual bird by matching the carbon and hydrogen isotope values in two tail feathers with the winter base-maps of these same isotopes in Africa. Each time after a bird molts, the local isotopic patterns are fixed into their new, growing feathers through their diet. The plants they eat carry the isotopic signature of the area’s water and soil, and that means each bird itself provides spatial information about its migration route. The birds in this study are summer visitors in Israel, and they winter and molt in Africa.
For both birds, the researchers found a positive correlation between migration distance and new neuronal recruitment in the brain regions examined, but the doves and warblers incorporated the new neurons differently. New neurons in reed warblers – lone nocturnal migrants – were mostly found in the hippocampus, which is associated with navigation. For turtle doves – who migrate in large flocks during both the day and night – the new neurons were taken up by the nidopallium caudolateral, an area that’s also associated with communication.
Image in the text: Reed warbler. Asaf Rahamim