V-shaped formations of migrating geese often herald the beginnings of spring or fall for many Minnesotans. Other bird watchers notice the return of robins or the exodus of orioles on their way to another winter in the tropics. In his new book "Living on the Wind: Across the Hemisphere with Migratory Birds" ornithologist Scott Weidensaul says the journey many birds make is nothing short of miraculous. Equally amazing is the short time they have to rest, raise a family AND bulk up for their next big flight.