Maine is home to two members of the deer family (the Cervidae family): moose and white-tailed deer. Also in that worldwide family there are elk, caribou, and various other species of “deer.” All family members apparently use their tails to swat flies, but only the white-tailed deer use their rear appendages to communicate significantly, according to the literature that I’ve seen.
As deer-watchers say, white-tails use their tails “to flag” messages by raising and flaring their white tails and buttocks areas. (Think of the old semaphore signaling systems of messaging with flags and other visual objects.) Researchers and hunters report a variety of messages that white-tails send by flagging, singly and as a group.
From an evolutionary standpoint, one of the more intriguing white-tail communications is the “I-see-you” message to predators, human and otherwise. This is thought to discourage pursuit by the predators who should realize that they are slower and should not waste valuable energy on a difficult, and eventually useless, chase.
There also apparently is the white-tails’ use of their highly visible raised white tails and exposed rumps as a general warning or notification to other nearby white-tails. This flagging often is accompanied by grunts, bleats, and other sounds that may make the message more comprehensive to the other deer as to what and where the threat or object of interest is.
Flagging is thought to be used for community purposes by white-tails, as well, especially by females that travel in groups. It can help them stay together when browsing or fleeing. It also can make it easier for fawns to follow moms in flight. (Images taken in Brooklin, Maine, on April 7, 2025, and April 24, 2017.)