Ethnographers recorded in the 19th and early 20th centuries that common folks in eastern Slavia believed that souls of dead people could move into bodies of animals and new born children if children were born at the time people died. Souls of good people moved in good animals, while souls of bad people moved in bad animals such as crow. Belarusians believed that souls of children could move to souls of other newborn children. Ukrainians believed that dead can reincarnate in ant, bird, animal, fish, and only then in man. People of Volyn believed that God can reincarnate a person for bad deeds in an animal.
More here: Метемпсихоз у восточных славян // Harvard Ukrainian Studies. — Vol. 28. — No. 1/4. Rus’ Writ Large: Languages, Histories, Cultures: Essays Presented in Honor of Michael S. Flier on His Sixty-Fifth Birthday (2006). — PP. 639—650.