Trail of Cthulhu: Eternal Lies
Little are known about these, as only theories can be placed together. Jonathan Brooks, wealthy cult figure living in Mexico City, apparently raised a variety of grackles and blackbirds. At some point he began feeding them Nectar as well as human body parts. Lord Edward Homeward discovered that through a series of conditioning and rituals dedicated to some Mythos entity, the birds likely became avatars of a Major Mouth. While not given any official name, their hellish origins indicate these things would be dangerous and best avoided.