According to the Aberdeen Bestiary (as well earlier texts such as The Physiologus), the Caladrius is a snow-white bird that lives in kings' houses. Supposedly, the bird refuses to look at any patient that is not going to make a full recovery.
It is said to also be able to take the sickness into itself and then fly away, dispersing the sickness and healing both itself and the sick person.
This is said to be analogous to Jesus Christ, whose crucifixion is said to have drawn out "the sickness" (sin, see Biblical sin-sickness analogy) and, through his "flight" from the grave, saved the sinner.
Basis of Origination
There are numerous theories as to where the legend of the Caladrius was started. One of them would be that it is merely the product of some overactive imaginations or that it was created purely as an analogy.
Another is that the Caladrius is based on a real bird. According to the descriptions of its being completely white with no black on it, it is possible that it was based on the dove, or possibly some sort of water bird such as the heron.
Caladrius Computing is also the name of an Australian data backup company.