Millions of mummified birds serving for religious purpose have been discovered from archeological sites along the Nile Valley of Egypt, in majority ibises. Whether these birds were industrially raised or massively hunted is a matter of heavy debate as it would have a significant impact on the economy related to their supply and cult, and if hunted it would have represented an ecological burden on the birds populations. Here we have measured and analysed the stable oxygen, carbon and radiogenic strontium isotope compositions as well as calcium and barium content of bones along with the stable carbon, nitrogen and sulfur isotope composition of feathers from 20 mummified ibises and birds of prey recovered from various archeological sites of Ancient Egypt. If these migratory birds were locally bred, their stable oxygen, radiogenic strontium and stable sulfur isotopic compositions would be similar to that of coexisting Egyptians, and their stable carbon, nitrogen and oxygen isotope variance would be close, or lower than that of Egyptians. On one hand, isotopic values show that ibises ingested food from the Nile valley but with a higher isotopic scattering than observed for the diet of ancient Egyptians. On the other hand, birds of prey have exotic isotopic values compatible with their migratory behaviour. We therefore propose that most mummified ibises and all the birds of prey analysed here were wild animals hunted for religious practice. A most significant feature of Egyptian religion was that most revered gods had the form of animals 1,2. A common practice was the mummification of dead people, since the Old Kingdom (ca. 2,543-2,120 BC) until the fourth century AD, in order to preserve the body from decaying after death and reach the afterlife. From the New Kingdom (c.a. 1,539-1,077), and more particularly from the Late Period (ca. 722-332 BC) the animals have been also widely mummified, and that for four main purposes: victual mummies as food for the afterlife, sacred mummies to preserve the remains of a living incarnation of a god, pet mummies to provide an afterlife to beloved pets, and votive mummies as offerings to the gods. The widespread use of votive mummies to pray the gods Horus (depicted as a falcon) and Thoth (depicted as an ibis) led to the production of millions of bird mummies, as evidenced by archaeological discoveries from at least 38 catacombs across the Nile Valley 3. Such production of bird mummies, which can be considered as intensive, raised the question whether these birds were farmed, thus leading to a significant impact on the economy related to their supply, or hunted with an obvious impact on the birds populations dynamics. It has been speculated that ibises were extensively farmed 4 , a view supported by contemporaneous reports of such practices 5,6. Moreover, finds of mummified ibises at all stages of development, from egg to juvenile to adult, support this suggestion. Ancient Egyptian textual references to « birth chapels » of ibises 7 have also raised the question of artificial incubation of eggs for breeding purposes 8,9 , open