My landscape ecological experience in the Tago-Tietar area and Africa with the Egyptian vulture would suggest the above as research hypothesis. Since WWII globalization has changed livestock farming fundamentally in Spain and elsewhere. Pertinent veterinary regulations  on carcasses in the open field are but one element of this change. The ubiquitous vulture restaurants may be an incomplete mitigation in such circumstances. Further, vultures seem very picky about where they build nests: rare exposed escarpments and tree canopies both with a view.