Wildlife poachers in Africa are targeting vultures by poisoning the carcasses of the dead animals they feed upon, causing an unprecedented decline in the birds' population.

Vultures are caught in the cross-fire of rampant poaching because they typically congregate at and feed on a freshly killed animal, drawing the attention of game rangers. To avoid this, poachers inject the carcass with poison, turning it into a fatal meal.

Nearly 1,500 of the birds have been killed in the past two years in southern Africa, conservationists say. Last year between 400 and 600 vultures were found poisoned from a single carcass in Namibia's Caprivi Strip. Last month 92 were wiped out in Botswana, while last week 15 died in South Africa's KwaZulu-Natal province.

The coalition said the situation is now "critical" with population decreases of up to 97% for some species in just three decades. Photograph: Martin Harvey/Getty Images/Gallo Images

A coalition of environmental and non-profit organisations warned recently that "widespread, increasing and mostly illegal use of poison is decimating African vulture populations, precipitating a biodiversity crisis with as yet uncharted human health consequences".

The coalition said the situation is now "critical" with population decreases of up to 97% for some species in west Africa in just over three decades, while 50-60% rates of decline were measured in the savannas of east Africa and southern Africa. Without scavengers such as vultures, carcasses are left to rot and disease spreads among other animals, with consequences for humans living nearby.

Last year between 400 and 600 vultures were found poisoned from a single carcass in Namibia’s Caprivi Strip. Photograph: Manoj Shah/Getty Images

Andre Botha, manager of the birds of prey programme at the Endangered Wildlife Trust, said on Thursday: "The poisoning of carcasses makes them particularly vulnerable. We can associate it with the poaching of large mammals like elephants and the poaching of buffalo for meat. If the poachers have little regard for large animals like elephants and rhinos, they probably have even less regard for vultures."

Vultures breed slowly, rearing only one chick per year, or in some species one chick every two years. Africa is home to 11 of the 23 species of vulture worldwide. Four species are now considered globally endangered and at risk of extinction, and three more are listed as vulnerable, according to the IUCN Red List of Species.

A coalition of environmental and non-profit organisations said the situation is now 'critical'. Photograph: suebg1 photography/Getty Images/Flickr RF

Botha added: "There's no doubt that there is great reason for concern and it will most certainly have an impact on the regional population. Governments are slowly becoming aware of the problem but a lot more needs to be done. I don't think it's realistic to stop poisoning altogether, given the current context of poaching, but if it's not managed properly, you could have massive losses."

In April Darcy Ogada, a Kenyan-based conservationist from The Peregrine Fund, told a summit in Spain: "In India the almost complete disappearance of vultures has resulted in a strong increase of the feral dog population and associated rabies incidence, which has been estimated to have cost $34bn in human health costs alone. It is shocking that nobody seems to be worried about the massive vulture decline we are now witnessing across Africa."