Tail Pulling: Crows (meaning Corvus, not just the crows with the common name “crow”) pull tails. It’s like they can’t help themselves. If there is a tail, it must be pulled.

Magpies in the genus Pica (the holarctic magpies) do this behavior as well, which is impressive, considering how much smaller they are. One advantage they have is a small size that lets them get off the ground and away from their target a lot quicker.

Usually when you see this behavior it’s in the context of food. A crow or magpie will pull another animal’s tail in order to distract it from it’s food and steal it (this sometimes occurs alone or in teams).

The behavior appears to be innate. By teasing larger animals, corvids can steal scraps of their food, chase them away from a tasty carcass, or simply test their aggression.

But honestly? Maybe they just do it for fun, or simply can’t help their natural inclination for causing trouble. Just another reason to love corvids ;)
(Corvidblog)