Gyps bengalensis (White-rumped Vulture) is my first critically endangered critter for the Conservation Biology course. G. bengalensis (= vulture of Bengal) was once thought to have been one of the most abundant scavengers in the world and was found throughout Central and Southeast Asia.
This species is now absent from SE Asia and declining throughout the rest of their range. The cause of the decline: the anti-inflammatory drug diclofenac that is used in livestock, causes renal failure in vultures. Vultures eat livestock. After the cow has died of course and cleaning up corpses is one of the important things vultures do. Not only do vultures remove a giant smelly rotting corpse from our landscape, consuming the corpse may reduce the incidence of diseases directly (by eating the organism) or indirectly by eating a food source for rats and feral dogs (which have several diseases that infect humans).
Diclofenac is now banned throughout most of this species' range and it appears that populations are now stabilizing.
Birdlife International: http://www.birdlife.org/datazone/sowb/casestudy/156
IUCN Red List account: http://www.iucnredlist.org/details/22695194/0