Spinner dolphins. Image: Mongabay

Take the dolphin quiz:

1. True or False? There is only one kind of dolphin.

False! There are at least 40 species of dolphins around the world, ranging in size from the kid-sized Hector’s dolphin in New Zealand to the giant orcas roaming the world’s oceans.

Bottlenose dolphin
Bottlenose dolphin. NASA, Public domain, via Wikimedia Commons

When most people think about dolphins they probably imagine the bottlenose dolphin – the most familiar dolphin in movies, television, and in aquariums. The bottlenose dolphin is named for its short, rounded nose that is shaped like a bottle. It lives in temperate oceans all over Earth. It is a good dolphin ambassador to humans, but it has many relatives that we should get to know also.

 2. True or False? All dolphins live in the ocean.

False! Most dolphin species live in the oceans of the world, but there are some freshwater species like the boto in the Amazon River in South America and the Indus river dolphin in India and Pakistan.

One of the river dolphin species, the Yangtze River dolphin in China, seems to be extinct. Scientists have looked extensively for remaining individuals in the 21 st century, but they have found none.

3. True or False? It is easy to sneak up on a sleeping dolphin.

False! In oceanic dolphin species, only half of a dolphin’s brain turns off while it sleeps. The dolphin keeps one eye open while the other eye closes and dozes. Then it switches eyes.

Maintaining a half-awake state is also important for keeping the dolphin’s blowhole open throughout its sleep cycle. Dolphins cannot breathe in water like fish can, so they must periodically surface and take a breath of air even while sleeping.

4. True or False? Dolphins sometimes use tools.

True! In a group of bottlenose dolphins in Australia, mother dolphins teach their daughters how to grab sponges and use them as shovels to stir up sea-floor dwelling fish. Next time you go to Sponge Depot and see a dolphin in the checkout line, now you probably know why it is there.