Fawns are helpless during the first weeks of life.  They depend upon their camouflage and an instinct to remain still for protection.  Any predator, especially a coyote, that discovers it, kills and eats the infant that has no defense.  This video shows a whitetail adaptation that adds an extra layer of protection by another species- mule deer.

Dominance Rivals

Mule deer protecting whitetail fawns is a cruel irony.  Where the two species share the same habitat, the whitetail is usually the more dominant and will out compete mule deer for that space.  Whitetail bucks have been reported to breed mule deer does, but not the other way around.  As an indication of the spread of whitetail deer into mule deer habitat, Todd Wilson, a hunter in Colorado, saw a whitetail deer doe last season at 11,000 feet.

Coyote Defense

This YouTube video is a “shortie but a goodie” as it shows the confrontation of a mule deer doe by a coyote, and a large one at that.  You’ll also want to read the background behind this phenomenon at https://www.insidescience.org/news/brief-sneaky-deer-moms-use-another-species-babysitters