"Any animal that comes back to the right place after a long travel, or comes back to the same place again and again following a major movement, is amazing," said Martin Wikelski, a migration expert at the Max Planck Institute. (Read about great animal migrations in National Geographic magazine.)

Many animals have a built-in magnetic system, "like a regular compass," said Wikelski, who is also a National Geographic emerging explorer. (National Geographic News is part of the National Geographic Society.)

However, much is still unknown about how animals navigate—for instance, no one can explain Holly's incredible journey, the New York Times reported.

But more and more research is pointing to the role of smell in navigation, Wikelski noted.

"It's one of