Tiny song birds hold the record:-http://phys.org/news/2012-02-featherweight-songbird-long-distance-champ.html-Also migration by magnetism in salmon:-http://www.sciencedaily.com/releases/2013/02/130207131713.htm-But the truly amazing part is the metamorphosis of the gills from fresh water to salt water to back again. Those gills must change to handle the salt:-"When migrating, salmon must transition from fresh water to sea water, and then back again. During each transition, the salmon undergo a metamorphosis that Putman says is almost as dramatic as the metamorphosis of a caterpillar into a butterfly. Each such salmon metamorphosis involves a replacement of gill tissues that enables the fish to maintain the correct salt balance in its environment: the salmon retains salt when in fresh water and pumps out excess salt when in salt water."-How did this evolve?