I recently wrote down in a notebook all I could find in Barber's Vampires, Burial and Death regarding Romanian beliefs and also beliefs in general concerning animals.

In Romania, it was believed that a person born with a caul (amniotic membrane still attached to the head and forming a veil), a small tail, or with hair covering his or her body was destined to become a vampire after death. Such people were called strigoi vii [singular: strigoi viu], which means "living vampires". A "dead" (or rather, as we say, "undead") vampire was called a strigoi mort. Romanians believed that the soul of a strigoi viu had the ability to voluntarily leave its body at night. Sometimes such souls appeared as a sparks traveling through the air, but it was also said that they took the appearance of flying insects or higher animals. The strigoi vii were usually not associated with blood sucking. But they could steal the vitality of their neighbour's crops, bee hives, and even the leaven of their bread and transfer it to their own. Sometimes it was said that they took animal form by stealing the form from the animal itself.

The Romanian word strigoi derives from the Latin word stryx. The ancient Romans believed in "witches" whom they called striges [singular: stryx] who transformed into screech owls at night to prey on unattended infants by drinking their blood and sometimes also eating their internal organs.

Regarding butterflies, Barber at least mentions a Serbian belief that a "vampire can transform into a butterfly" as well as general belief among Balkan people in general that the soul can leave the body in a form such as a butterfly. (See page 72.) Regarding chickens, all I can find in Barber's book is that "among the Arumunes of Romania" it was believed that a black hen jumping over a corpse would cause it become a vampire after burial. It is also mentioned on the same page that some Romanians believed that a bat flying over a corpse had the same effect. (See page 33)

Belief in the ancient Roman striges survived in the Balkans into the early 20th century, Albanians believed in the shtriga, an elderly woman who preyed upon infants by drinking their blood, also caused adults to wither and die, and who could change into a moth, fly, or bee at night. Albanians typically blamed a shtriga for what we call "cot death" or SIDS (Sudden Infant Death Syndrome). In Higher Albania, Elizabeth Durham (originally published in 1909 but reprinted in 1985 by Virago Press, London) writes how she found that many Albanian infants ironically died in their cots from being so over-protected from the Shtriga with swaddling blankets – they grew pale and sick from lack of fresh air and sunshine. She tried to persuade some mothers to reverse this, but they could not be persuaded to depart from tradition.

The "modern Greek" version was the strigla, an old woman who changed into a crow. In regard to the original question, the most interesting example is from Serbia and Montenegro – the veshtiza [plural: vestize].

According to a description of the veshtize in an old book that I have, Hero Tales and Legends of the Serbians by Woislav M. Petrovich, 'Late Attaché to the Serbian Royal Legation to the Court of St. James' (London: George G. Harrap & Co., 1914), the veshtize "are supposed to be old women possessed by an evil spirit." The soul of a veshtitza leaves her body at night while she sleeps and "wanders about till it enters the body of a hen, or, more frquently, that of a black moth." In the body of such a creature, she flies about until she finds a home where there are infants or young children – "its favorite food is the hearts of infants." At midnight, the vestitze would sometimes flock together in the branches of some tree and hold a meeting while they snacked upon what they had gathered earlier in the night. "An old woman having the attributes of a witch may join such meetings after having complied with the rules prescribed by the experienced veshtitze, and this is done by reciting certain stereotyped phrases."

The Vampire Book: The Encyclopedia of the Undead by J. Gordon Melton, p. 570, gives some more details concerning the vestiza. Melton's sources include not only Petrovitch's Hero Tales and Legends of the Serbians but also a 1924 article by Edith Durham published in the British anthropological journal Man. Melton doesn't say anything about hens, but says that the soul of a sleeping veshtitza "wandered at night and either inhabited a moth or a fly. Using the flying animal, the witch entered into the home of neighbours and sucked the blood of victims. The victim, over a period of time, grew pale, developed a fever, and died."

It isn't clear if the word "hen" was used by Petrovitch in the narrow sense of "a mature female chicken" or in one of the broader senses of the word ranging from "mature female domestic bird" to "any female bird." But I do find it conceivable in my own mind that mature female chickens might have sometimes been suspected by Serbian peasants of being possessed by veshtize. While growing up in a small town in rural Iowa, I found that chickens, if not prevented from doing so, would roost on warm nights in the low branches of trees and shrubs of groves which many farms had bordering the farm yard. Also, if in the Balkans there was a general problem with keeping chickens and other animals from entering the house and jumping over a corpse laid out prior to the funeral, there must have also been the possibility that a chicken hen could enter a house at night and find a comfortable roosting place over a swaddled baby sleeping in its cradle. Imagine the horror felt by a superstitious mother finding a chicken sitting on the chest of her baby, or finding a hen frantically dashing towards an open window when the infant woke up and began crying in terror. If the infant was found dead or grew sick and died after a time following such an event, it would be likely that the chicken – or whatever being might have possesed it or otherwise tranformed into the chicken – was considered to be the cause.

Not only live witches might be associated with such belief.

The Gypsies believed that the vampire was the soul of a dead person (mullo) who departed from the buried corpse at night. This concept was shared by at least some Serbs, Romanians, and Bulgarians – and some Serbs believed that undead vampires could take the form of a butterfly. Gypsies in Sweden, at least, believed that a mullo could transform into a horse or a bird. Gypsies in the Balkans believed also that animals could become vampires after their death and that watermelons and pumpkins could become vampiric if kept too long.

In Montenegro, north of Albania, the majority of people are ethnically identical to Serbs. They believed not only in the veshtiza but also that a corpse could become a vampire if an animal jumped over it, and that the undead type of vampires returned to their graves in the form of mice. (The soul leaving a sleeping body in the form of a mouse is a widespread motif). One tribe of Montenegrans believed that vampires spent a part of their time in the form of wolves. (It was once believed in old Livonia, in what is now Latvia, that the souls of "werewolves" left their sleeping human bodies and took possesion of a wolf's body.)

I could give many more examples and exotic elaborations. Anyway, I would not be too surprised to find that somewhere, somehow there was once belief in vampires returning from their graves in the form of chickens.

Sources:
Vampires, Burial and Death by Paul Barber
The Vampire Book: Encyclopedia of the Undead by J. Gordon Melton