The ruddy turnstone

New lightweight tracking devices allow scientists to follow a tiny bird's round-the-world migration:

Tracker devices can be fitted on birds either by fixing them to a leg or by sticking them to the back. All the ruddy turnstone had them attached to legs because tests showed that after spending the Australasian summer fattening up to their maximum weight of about 190g they were "as round as tennis balls" and the backpack style wouldn't stay on.