Vanishing vultures may threaten public health

When we think of wildlife conservation, vultures rarely top the list. Yet these birds – often misunderstood and overlooked – may be more essential to public health and ecosystems than we ever imagined.

A recent study out of Costa Rica has uncovered just how vital they are, especially when it comes to getting rid of dead animals quickly and safely.

How vultures speed decay

Scientists from the University of Exeter, working in collaboration with OSA Conservation in Costa Rica, designed a simple but revealing experiment.

The team set out to observe how animal carcasses decomposed with and without vultures present. Using domestic pig carcasses, they monitored the decomposition process across forest and grassland settings between September 2023 and June 2024.

The researchers left half the carcasses in the open for all scavengers to access. They placed the other half inside cages that prevented vultures and other large animals from reaching them. Cameras and insect traps were installed at each site to track both animal activity and insect populations.

The findings were both surprising and concerning. In the open sites where vultures had access, the pig carcasses lost an average of 9.5 kilograms per day.

In contrast, the protected carcasses – off-limits to vultures – decomposed at only 4.8 kilograms per day. That’s a dramatic difference.

Flies thrive without cleanup birds

As carcasses lingered without vultures, one thing became clear: flies moved in to fill the gap.

Sites where vultures were excluded saw fly populations nearly double. Dung beetle numbers stayed the same, and the researchers rarely observed larger vertebrate scavengers like pumas, ocelots, caimans, or coyotes were rarely observed.

“This research underlines the unique and irreplaceable role that vultures play as nature’s cleanup crew,” said Julia Grootaers, co-author and Behavioral Ecologist at the University.

The study showed that other scavengers simply weren’t stepping in. Without vultures, decomposition slowed down significantly, giving flies more time to reproduce and mature. And this has health implications.

“These apex scavengers have specialized and highly acidic digestive systems that can destroy many of the pathogens found in carrion, thus mitigating the spread of disease from carcasses to other wildlife, livestock, and humans,” Grootaers said.

Health risks without vultures

According to the researchers, the extra time it takes for a carcass to decompose in the absence of vultures can increase the chances of disease transmission.

Flies that breed in these carcasses can carry harmful bacteria like E. coli and salmonella. They may also become vectors for diseases such as botulism and anthrax.

“Our results demonstrate that intact scavenger communities, with vultures, invertebrate and microbial decomposers, efficiently decompose carcasses at double the rate compared to when it is insects and microbes alone,” said Dr. Chris Beirne, Director of Wildlife Programs at OSA Conservation.

“And it’s apparent that in Costa Rica, other large vertebrate scavengers do not drive decomposition in the food chain and that is consistent with what we see in other regions, including Kenya and northern Spain.”

Vanishing vulture populations

While there’s been widespread attention on vulture declines in Africa, Asia, and Europe, the Americas have largely flown under the radar. That needs to change.

Many species in North, Central, and South America are now facing growing threats from habitat loss, poisoning, and human disturbance. Without proper monitoring, their populations could plummet before we fully understand the consequences.

“While dramatic vulture declines have already been documented across Africa, Asia, and Europe, this study raises concerns about the overlooked vulnerability of their American counterparts,” said Greta Hernandez of Universidad de Panamá.

“And the findings highlight the urgent need for deeper research into vulture population trends in the Americas, the critical ecosystem services they provide, and the conservation action needed to safeguard these silent stewards of the environment.”

The takeaway is simple but powerful: vultures aren’t just scavengers – they’re a key line of defense against disease and environmental decay. Losing them means losing one of nature’s most efficient recycling systems – with real consequences for the world we share.

The full study was published in the journal Ecology and Evolution.

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