The caladrius is an all-white bird that lives in the king's house. If it looks into the face of a sick man, it means that he will live, but if the caladrius looks away, the sick man will die of his illness. To cure the sick man, the caladrius looks at him, and drawing the sickness into itself, flies up toward the sun, where the disease is burned up and destroyed.

There is confusion in some manuscripts between the caladrius and a bird with a similar Latin name, calendris (the lark), with the caladrius being incorrectly called calendris.

The caladrius represents Christ, who is pure white without a trace of blackness of sin. Because the Jews did not believe, Christ turned his face from them and toward the Gentiles, taking away and carrying sins to the cross. Christ turns away from the unrepentant and casts them off; but those to whom he turns his face, he makes whole again.

The caladrius is usually illustrated as a white bird (sometimes other colors) perched on or near a bed where a sick person is lying. The person is sometimes a king, wearing a crown. The bird is shown looking toward or away from the person; in some cases there are two birds, one looking toward the person and one looking away. Sometimes other people are shown near the bed, reacting with happy or sad expressions depending on which way the bird is looking.

The caladrius predicts if a sick person will recover or die. The lower part of its leg cures dimness of the eye.

Some modern writers say the caladrius is the skylark.