Bone Birds were designed by Dr Abbey.

While the bone birds look a lot like birds made out of bones, all the theories about them assume them to be neither bones, nor birds. One school of island thought has it that these are in fact demons. Some islanders are confident that bone birds do not exist and will refuse to admit being able to see them. The Hopeless Maine Scientific Society considers them to be some sort of insect. Unlike (other?) demons, bone birds maintain fixed forms and look similar to each other. They gather in small flocks and tend to favour isolated open spaces – hilltops and clifftops especially. They are highly vocal, making unpleasant screeching noises when alarmed, and eerie whispery noises the rest of the time. While they tend to avoid people, they will attack anyone who comes into their nesting sites. During nesting season (which does not come at a coherent frequency), they will also attack you for the contents of your washing basket or laundry line. They take hats, and anything else easily removed, to use as nesting material. They aren’t gentle about this, and while they don’t eat people, they will bite people.
