What visual warning signal does a white-tailed deer make by raising its tail?

A white-tailed deer’s raised-tail warning display is called tail flagging.

When alarmed, a deer lifts its conspicuously white tail, exposing the bright underside to animals nearby. The movement can signal danger to other deer and may also make the startled animal more noticeable as it runs away. In groups, one deer’s display can trigger vigilance or flight in others.

Tail flagging is especially associated with white-tailed deer, whose common name refers to this visible feature. The white underside is normally hidden when the tail hangs down, but becomes prominent during alarm. Deer also communicate through scent, body posture, foot stomping, and vocal sounds such as snorts and bleats.

The display is not an infallible predator detector. Deer may raise the tail in different situations, including excitement or uncertainty, and the exact behavior varies with context. “Tail flagging” describes the signaling action, not a separate vocal call.