When wolves were reintroduced to Yellowstone National Park in the United States after being absent nearly 70 years, the most remarkable "trophic cascade" occurred. What is a trophic cascade and how exactly do wolves change rivers? George Monbiot explains the process.

Beyoncé performs "Single Ladies (Put a Ring on It)" live in Central Park as part of the Good Morning America 2011 Summer Concert Series.

The song "Airplanes" is a collaboration between American rapper B.o.B, and Hayley Williams, lead singer of American pop punk band Paramore. Enjoy!

Barney never fails to impress the group with the lengths he'll go in order to get a woman interested in him.

Red simply doesn't want to wake up for school! David struggles to get him out the door, but there is something important that he is forgetting...

This video shows us that Shakespeare invented over 2000 new words and phrases, such as "eyeball," "anchovy," and "puppy."

British singer Ellie Goulding visits radio station 104.3 MYfm in Los Angeles to deliver an exclusive live performance for a few lucky listeners.

From time to time, we give celebrities a chance to read some of the mean things people tweet about them. We extended that same offer to our Commander in Chief, who happily agreed. This is an all President Obama edition of #MeanTweets.

"Roxanne" is a song by English rock band The Police. Written by lead singer and bassist Sting, the song was released as a single from their debut album Outlandos d'Amour. It was written from the point of view of a man who falls in love with a prostitute.

For the body and the mind: Try out some knee exercises and learn some new vocabulary related to posture and fitness. Enjoy!

Why would a killer whale go after a great white shark? Enter Alisa Schulman-Janiger, a biologist who is very familiar with the different families of killer whales off the coast of California.

Steve Skaith sings "The Men Below," a song about a mining strike in England in the 1980s.

If you don't feel like putting the time and effort into baking a whole cake, then try the fantastically fun and simple Two Minute Mug Cakes! All you need is a microwave, a mug, and a few ingredients, and you have an instant treat to enjoy on your own or to make for your best friends!

"Just Give Me a Reason" is a song recorded by American singer and songwriter Pink, featuring Nate Ruess of the band Fun. It is a pop ballad about the desire to hold on to a relationship even when it appears to be breaking down.

UNICEF Goodwill Ambassador Katy Perry delivers a special weather report on the devastating effects of climate change for the world’s children.