According to How Stuff Works:

Wolves howl as a form of long-distance communication, conveying a range of information. Because of the high pitch and the suspension of notes, the sounds of wolf howls can carry as far as 6 miles (9.6 kilometers) in the forest and even 10 miles (16 kilometers) across the treeless tundra.

Wolf howls serve as GPS systems, sing-alongs and fire alarms — all rolled into one. In fact, the purpose of wolf howls isn’t terribly different from the reasons humans raise their voices to the wind. In general, the primary reasons why wolves howl include:

– A rally cry for the pack to meet up
– A signal to let the pack know of a wolf’s location
– A warning for outside wolves to stay out of a pack’s territory

 

In this video we see Alawa (front) and Zephyr, captive-born gray wolves at the Wolf Conservation Center (WCC) in South Salem, New York.