The isida is found in some medieval encyclopedias. It is a small bird with beautiful green, blue, sapphire and red feathers. It lives near water and builds its nest in a hole in the ground. It is said that if you remove the bird's skin with the feathers still attached and stick it to a wall, the feathers will continue to change as though the skin was still alive.

The isida signifies those who refused to abandon their bad manners and old customs while living, whom the dead will certainly change, because for pleasure they will obtain punishment, for vain joys pain, for transitory evils eternal hell. [Thomas of Cantimpré]