Blue whales are the biggest mammals in the world. They grow to be 100 feet long. They weight up to 200 tons.

Blue whales can be found in all the oceans on Earth. Like all mammals, they breathe air. They come to the surface of the water to breathe. They float in the water, which supports their large size.

Groups of blue whales are called pods. Most of the time, blue whale pods are very small. Sometimes the whales travel by themselves.

Blue whales eat tiny shrimp-like animals. They are called krill. Whales can eat close to four tons of krill a day. They need that much food to fuel their giant bodies.

Sadly there are not very many blue whales left. People hunted them for many years. People wanted their blubber, or fat, to make oil. They also wanted their bones to carve. Blue whales are now protected. They are still an endangered species.

Blue whales have a unique voice. They make sounds that are like moans and grunts. These sounds can be as loud as an airplane. They are very low, so humans cannot always hear them.

One mysterious thing about blue whale sounds is that they are changing. They are getting lower and lower every year. Scientists do not know why. One guess is that it has to do with how many whales there are in certain areas. Maybe scientists will solve the mystery one day. But for now, blue whales are keeping their secret.