At least 648 vultures have been found dead in Guinea-Bissau over the last several weeks due to unexplained circumstances. Conservation experts warn the mass mortality event could be a “catastrophic blow” to the conservation of several species already on the brink of extinction.

“A vulture conservation disaster is currently occurring in Guinea-Bissau with over 600 vulture deaths this week,” wrote international non-governmental organization Vulture Conservation Foundation (VCF) in a Facebook post. Towards the end of February, initial reports came in of around 200 individual birds found dead throughout the province of Bafatá, a north-central region in the West African country. At first, the organization suspected poisoning, which it notes is a common occurrence in the area.

“It started with 200, then 400, and the current death toll is at 648 mortalities – a catastrophic blow to their conservation. The relevant authorities have swiftly responded to the incident, but worryingly the cause of mortality is not yet identified.”

But dead birds were reported across several areas, further complicating the case. Instances of poisonings tend to be more concentrated to one area.

“In recent years, we have unfortunately faced several incidents where hundreds of vultures died around a poisoned carcass, usually due to human-wildlife conflict with predators, we first thought this was such a case”, said André Botha, the Endangered Wildlife Trust Africa’s Vultures for Africa Programme manager, in a statement.

At this time, it is unclear what is contributing to the mass mortality event; whether it could be a disease or extreme weather event is yet to be determined.  

African vulture species have seen a dramatic decline in recent years. According to VCF, the International Union for Conservation of Nature (IUCN) has listed three species as Endangered and four as Critically Endangered in the region. It appears that the Hooded vulture (Necrosyrtes monachus) is the vulture species most impacted by whatever is causing the deaths, posing a “fatal blow” to its conservation status at national and regional levels. Vultures also play a vital role in ecosystems, by disposing of dead animal carcasses that may spread disease. To lose them will have a knock-on effect on their habitats.

Authorities responded to the event by incinerating 135 vulture carcasses in order to minimize the risk of potential disease spread.

“The authorities so far have been very responsive and acted quickly – this needs to be maintained until the cause of mortality is found,” said José Tavares, VCF´s director.  

VCF says that the World Health Organization in Guinea-Bissau is determining whether the bird deaths pose a risk to public health. IFLScience contacted doctors with the local WHO office but has not received a response at the time of publication. The conservation organization adds that it is crucial to identify the cause of death and to continue incinerating dead vultures to prevent mortality and further contamination to safeguard public health.