Scientists think there are many different reasons. One of the reasons is that they are getting ready for a hunt and they get excited. Another reason is that they have gotten lost from their pack and are trying to locate it. One scientist observed a mother wolf separated from her young on one side of a river, howling to guide her pups to a safe spot to cross. Wolves will also howl to signal their territory to other wolves.
Some people believe that wolves howl because they are happy.
For instance, author R.D. Lawrence said that when a mother wolf is giving birth to her pups inside the den, the other wolves outside will get really excited and start howling, as if they are singing. Our thanks to Conner Quinto and to the National Science Foundation for our Young Producers Contest 1999. We're Block and Byrd for Earth and Sky.