April 11 (UPI) -- By migrating out of the tropics and back to Europe to mate and raise their young, many birds species avoid having to deploy a hefty immune system.
When scientists analyzed the immune systems of sedentary birds species in Africa and Europe, as well as migratory birds that winter in Africa but return to Europe to breed and raise their young, they found birds living in the African tropics had more varied, robust immune systems.
Birds in Africa are exposed to a greater diversity of diseases, so a more capable immune system makes sense. But researchers also found migratory birds had the same simplified immune system as sedentary birds in Europe -- an unexpected discovery.
"What really surprises me is that the immune systems of migratory birds show a similarly low variation to that of European sedentary birds," Helena Westerdahl, a researcher at Lund University in Sweden, said in a news release. "After all, migratory birds don't only need to resist diseases in Europe, but also during their migration and in the tropics."
Researchers say their findings, published this week in the journal Nature Ecology & Evolution, suggest scientists have underestimated the drawbacks of a strong and complex immune system.
Hardier immune systems increase the risk of autoimmunity and other immune system disorders like chronic inflammation. Young birds, being exposed to diseases for the first time, are most at risk, but because migratory birds leave Africa to birth and raise their young, they're able to minimize risk without adopting a complex immune system.
"When the migratory birds breed, they have moved away from many diseases and therefore do not need an immune system that is equally varied," researcher Emily O'Connor said. "Another advantage is that the risk of damage caused by the immune system drops considerably if the immune system is less complex."
Because avian immune systems are built up similarly to human immune systems, the research could offer new ways of understanding the evolution of the human immune system.