The Arctic tern is impressive, but it doesn't always take a marathon migration to impress researchers--especially if you're studying a notoriously lazy swimmer like the saltwater crocodile. A team of researchers that included the late Steve Irwin (aka "Crocodile Hunter") discovered that Northeastern Australia's crocodiles sometimes swim over 6 miles in a single day. Surprised by these findings, the researchers searched through older tracking data and found that one crocodile averaged nearly 15 miles a day. But there is a catch: a majority of the time, these tagged crocs followed the current flow, thereby minimizing the amount of energy they needed to use.

The migration map above shows the routes of three adult saltwater crocodiles that moseyed their way around Australia's Cape York Peninsula, with "st" and "fin" representing where each track begins and ends. Croc number one managed that entire trek in 25 days, while the second croc rounded the peninsula in 15 days, and the third made a 5-day dash. The arrows show the kinds of current directions the crocodiles experienced while traveling. This go-with-the-flow mentality is somewhat surprising considering that it's specific to long-distance-swimming crocodiles--for short journeys, crocs show no preference for current directions.