This coyote is afflicted with mange. Mange is an infestation of scabies mites which suck blood and cause the hair to fall out. It is spread by contact and can spread rapidly though a population of coyotes or wolves. If severe enough, the disease causes death in the winter when infected animals die from the cold.
I don't know if coyote's exposed skin is always black like this or whether his skin turned black from repeated exposure to the cold. Some people thought that this animal was a wolf because he looked black. I think this coyote should be killed before it spreads mange to other animals.
The Druid Pack of Yellowstone Wolves all died a year ago after catching mange.
Mange in humans is called Scabies or the Itch and can spread rapidly in school children. The elk wintering on the National Elk Refuge sometimes get Scabies as well. I am not sure if the same mange mite can infect various species or if the mites are specific to a particular host. Scientists disagree whether mange is endemic to North America or if it was brought in by white settlers and their livestock.
Early settlers in the west reported that the Bighorn Sheep population was decimated when wild sheep caught Scabies from their domestic cousins.
It is not a pretty way to die.