White tail deer have a white tail to warn other deer if a predator is nearby. When deer think that a predator is close they make a snorting sound with their nose, as they run away they wave their tails kind of like a flag. When the other deer see it they know to run too even if they did not hear the snort. The rest of the deer’s fur is brown so they can blend in with the forest, the white underside of their tail is easily seen which makes it a perfect warning signal.