So, a long time ago, tired of seeing people getting into fights over whether or not cleft tails make Pikachus female or dickgirl or whathaveyou, I created a tag for it. This tag was helpful, because it allowed us to keep track of male or ambiguous pikachus who have cleft tails, but this wasn't a trait specific to Pikachus. Any character with a tail could have a cleft at the end of it, after all.

However, the term "cleft tail" originated with birds.
post #1192549
Especially in birds who fly, their tail feathers would typically move in two, rudder-like segments, to help them steer themselves in mid-flight.
post #794650 post #629130
Of course, not every instance where the tail feathers of flying birds are shown will have this rudder-like split. Should we still count these ones, since there is a split down the center?

post #1148769
Be careful about tails like an Espeon's, though! This is a forked_tail, not a cleft one!