How does a white-tailed deer use its tail to signal danger?

The white-tailed deer (Odocoileus virginianus) uses a visual alarm signal known as "flagging" to communicate the presence of a threat.12

When a deer senses danger and begins to flee, it raises its tail to reveal the distinct white fur on its undersurface. This behavior is a common alarm signal among mammals. While biologists generally categorize this as a response to fright, there is ongoing scientific debate regarding the precise meaning of the signal; it typically accompanies a flight response, though it may occasionally precede an attack if a predator is within a critical distance.12