Hundreds of pilot whales managed to return to the water after being stranded on a New Zealand beach.
About 416 whales were stranded Friday; many got free but were then restranded. Hundreds of whales died. It was the third largest mass stranding in New Zealand history.
But how do whales and dolphins — who are naturally expert navigators — end up getting beached?
Individual animals will strand themselves for simple reasons, including illness, injury and old age.
But mass strandings — like those in New Zealand — are a bit more mysterious.
Humans might have a hand in some whale strandings. Loud sonar can cause them to flee and beach themselves.
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But other factors could play a role as well. Whales and dolphins are, for the most part, social creatures. And some species follow a leader, which could lead them to shore.
Environmental factors could also be to blame. Scientists think changes in the Earth's magnetic field could disorient them. And red tides — poisonous red algae blooms — might have been responsible for stranding over 300 whales in Chile in 2015.
