Conservationists have long warned of increasing threats to Africa's populations of rhinos, elephants and other wildlife. Now add vultures to the list.

BirdLife International, a conservation group, said Thursday that four of Africa's 11 vulture species have been listed as critically endangered this year on an international "red list" of species under threat. It says the status of another two vulture species has also dropped from vulnerable to endangered.

BirdLife International says vultures feed on carcasses poisoned by livestock herders to kill predators on the ground, or are poisoned by poachers who fear the presence of vultures will alert authorities to the carcasses of illegally killed wildlife. Vultures are also killed for their body parts which are used in traditional medicine.