In southern Slavic regions there is a vampiric REVENANT known as a vudkolak (“wolf ’s hair”), but this word is also used to refer to a werewolf. When a werewolf dies, on the night of the next full moon it will rise from its grave as this type of vampire. However, if a bird were to fly over the body of an unburied person, he too will also become a vudkolak. To prevent this from happening, a traditional honor guard made up of family and important people of the community will keep a careful vigil over the body all night long in order to ensure its safety. Should they fail in their task, on the nights of the full moon the vudkolak rises from its grave and shape- shifts into a werewolf in order to hunt humans to feed upon. The grave of a vudkolak can be detected as the grave that crows will not go near.

Source: Guiley, The Complete Vampire Companion, 10; Perkowski, The Darkling, 38