It only takes one Crow to make a mob

The Cinereous Vultures in Bulgaria are constantly mobbed by Hooded Crows. They don’t get a moment’s peace.

The Crows are compelled to do it.

This one is getting a right-good pecking.

Hooded Crows have probably been mobbing other birds since they were entirely different species, right back in evolutionary time. And this Hooded Crow has no intention of disappointing its ancestors.