Kappores

Rashba  (1:295) Mar, the Master already wrote: I have found that this custom of kappores was widespread in our town, that they would slaughter an old chicken for the sake of atonement over a young man, they would cut its head and hang it by its feathers at the door with garlic. And this is nonsense in my eyes like the ways of the Ammorites. I've pushed this custom out and by the grace of Heaven, they listened to my word and none of these practices remain anymore in our city.I have heard from different people from Ashkenaz who sit with us in the beit midrash (house of study) that all of the rabbis of their land do this on erev Yom Kippur...I still withheld this from our town.

Shulchan Aruch(Orach Chayim 605:1)That which people are accustomed to perform kapparah before Yom Kippur by slaughtering a rooster for each male and to say verses over it, you should prevent the custom.

Rema (OC 605) And there are those from the Geonim that write about this custom, and similarly it is written from many Achronim, and so is the custom in all these countries  - and you shouldn't change, for it is an ancient custom.