Gray wolves were once common throughout all of North America, but were exterminated in most areas of the United States by the mid 1930s. Today, their range has been reduced to Canada, Alaska, the Great Lakes, northern Rockies and Pacific Northwest.
Wolves have a complex communication system ranging from barks and whines to growls and howls. While they don't actually howl at the moon, they are more active at dawn and dusk, and they do howl more when it's lighter at night, which occurs more often when the moon is full.
Did you know that wolves have unique howls,like fingerprints, that scientists (and other members of their pack) can use to tell them apart?
Source: Defenders of Wildlife