Twice a year in southern Sweden, the skies fill with migrating birds. Streams of them funnel through the country’s southern tip, traveling to and from wintering grounds in Africa and nesting grounds in Europe.

It’s a tough and strenuous journey in the best of times. So ornithologist Emily O’Connor wondered: How do these compulsive wanderers deal with infections?

“One of the big biological questions regarding migration is how these birds cope with diseases in two entirely different geographical regions,” said Dr. O’Connor, a researcher at Lund University in Sweden.

“If I was to travel from my home in Europe to Africa for a holiday, then I would need all sorts of vaccinations to protect me from diseases. But migratory birds move regularly between Europe and Africa with no help from medicine.”