Researchers may have uncovered a 5th reason that ancient Egyptians mummified and entombed animals. Until now, animal mummies have fallen into 4 categories:
Sacred animals, like the birds in the middle image, were worshipped in animal cults as incarnations of deities and carefully mummified after death. The falcons in the photo represented Horus and the ibis represented Thoth. The most cumbersome sacred animal to mummify was the Apis bull, an incarnation of Ptah, creator of the universe.