Caladrius (Angelos dhalion) originated somewhere in Western Europe; the earliest reports put them in the vicinity of Greece, although this may be a matter of documentation, and not evolution. Like all known members of family Avinidae, they have become increasingly rare as mankind spread across the globe, being too distinctive to easily blend with the human population. Reports exist of Caladrius amputating their own wings in order to hide. It is unclear whether this is truth, or one more unpleasant fiction ascribed to a species that has been traditionally haunted by stories.
The Caladrius are most often represented in mythology as "the Caladrius bird," a magical, white-winged bird with no human characteristics and magical healing properties. The Caladrius themselves do not often object to this, as, when they are taken for albino harpies, they are less likely to find their feathers harvested to be sold on the black market. Caladrius are often nervous around humans. It's difficult to blame them.
BIOLOGY
Caladrius are members of the family Avinidae, which branched off from the rest of the primates shortly after family Hominidae. It has been proposed that the caladri, like all six-limbed mammals, did not actually branch off here, but evolved in a nearby parallel world before somehow migrating to our reality. The veracity of this theory cannot currently be proven, but is supported by our biological knowledge of the Avinidae, all of whom seem to have followed similar evolutionary paths which would not have been probable under this world's established biology.
Caladrius are omnivorous, but prefer a largely vegetarian diet, and get their protein primarily from beans, legumes, and high-fat fruits such as avocados. Female Caladrius eat more meat when gravid, although they mainly consume poultry and fish, avoiding red meat whenever possible. 
Caladrius are monotremes, laying two eggs a season, regardless of sexual congress. Unfertilized eggs are laid earlier than fertilized eggs, and are often used as a source of protein for females who are carrying young.
Like all Avinidae, Caladrius are hollow-boned, although only children and small adolescents are actually capable of flight. Their wings connect to their shoulder blades via a complex web of musculature which extends to their chests; female Caladrius tend to be small-breasted, and all Caladrius are thin by human standards, due to an increased metabolism. Caladrius do not have body hair, and the hair atop their heads appears to be downy feathers, made of the same modified keratin as the feathers on their wings. They are believed to be cross-fertile with other members of family Avinidae, but this has not, as yet, been confirmed. The few surviving Caladrius tend to be polite, private people, and we have not yet succeeded in getting one of them drunk enough to talk.
Caladrius are warm-blooded, and are resistant to most human illnesses. Their lifespan is somewhat longer than the human norm, but not so much so as to be remarkable among the known cryptid races.
NATURAL HEALING
The feathers of the Caladrius possess unusual healing properties which have never been duplicated. This explains the over-hunting of their species, as the feathers of a Caladrius can aid the healing of even mortal wounds.
DESCRIPTION
Caladrius resemble tall, thin, Caucasian humans with bird-like feet, white feathers in place of hair, and large white wings growing from their shoulder blades. They do not pass well as humans. Most Caladrius have orange, yellow, or pink eyes, resembling the eyes of rock doves. They are often considered quite attractive, although they rarely date outside their own species.
Artwork by Kory Bing.