Why Animal Scavengers Protect Your Health

Worldwide, populations of scavenging animals that feed on rotting carcasses are declining. Scientists are finding that this can seriously hurt human health. NPR science reporter Jonathan Lambert https://www.npr.org/people/703751120/jonathan-lambert has been looking into how human health is intertwined with scavenging animals and why these animals’ decline could lead to more human disease. Today, he brings all he learned, including how conservation could help, to your earholes. Check out more https://www.npr.org/sections/goats-and-soda/2025/07/11/g-s1-77052/vultures-hyenas-and-rabies-scavengers-diclofenac of Jon’s reporting on scavengers and human health. Interested in more science behind skincare products? Email us your question at [email protected] mailto:[email protected]. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:00Speaker 00

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• 0:17Regina Barber?

  You're listening to Short Wave from NPR. Hey, Short Wavers. Regina Barber here. And today, I'm joined by NPR science reporter Jonathan Lambert. Hey, John.

• 0:28Speaker 02

  Hey, Gina.

• 0:29Regina Barber?

  OK, so you're here today to make a case for scavengers, like vultures and hyenas, that they're good for human health? I mean, honestly, I believe it. They're usually smart. They clean up dead stuff.

• 0:41Speaker 02

  Yeah, totally. To me, though, health isn't the first thing that comes to mind when I picture a vulture hunched over the rancid, rotting flesh of a dead cow, tearing strings of lifeless meat from bone till there's nothing left.

• 0:54Regina Barber?

  I really love this visual you're giving me. Yeah, it's that rotting stuff laying around that's not good for us humans.

• 1:01Speaker 02

  Right. And scavengers' taste for that rotting stuff actually has major benefits for human health, which is maybe best conveyed by a little story.

• 1:09Regina Barber?

  Excellent. I love stories. Let's do this.

• 1:11Speaker 02

  OK, so we're going to India. Way back in the early 1990s, there were some 50 million vultures across India. But in the mid-'90s, they started vanishing. And over the course of several years, their numbers plummeted by like 95%.

• 1:26Regina Barber?

  95%. That is huge. So why was that happening?

• 1:31Speaker 02

  A painkiller for livestock that just happens to be toxic to vultures. Its patent ran out in 1993, and usage spiked once cheaper generics came onto the market. Vultures started eating dead cows to have the drug in their system, which led to a mass die-off.

• 1:46Regina Barber?

  Oof, that is terrible. OK, how did this mass die-off affect the area, though?

• 1:51Speaker 02

  Well, some researchers estimate that the absence of vultures led to hundreds of thousands of additional deaths in the five years after the crash.

• 2:00Regina Barber?

  Wait, human deaths?

• 2:01Speaker 02

  Yes, humans.

• 2:03Regina Barber?

  And you said hundreds of thousands.

• 2:04Speaker 02

  Yeah, yeah. It's one of the clearest examples of how scavengers are connected to human health. But it's far from the only one. And a new analysis suggests that many other scavengers are declining worldwide.

• 2:16Regina Barber?

  So today on the show, how human health is intertwined with scavenging animals.

• 2:20Speaker 02

  Why their decline could lead to more human disease and how conservation could help.

• 2:25Regina Barber?

  You're listening to Short Wave, the science podcast from NPR.

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• 3:06Speaker 00

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• 3:39Regina Barber?

  OK, John, so back to these vultures. How exactly did their disappearance lead to hundreds of thousands of people dying?

• 3:46Speaker 02

  The answer lies in the fact that vultures are really, really good at cleaning up dead bodies.

• 3:51Regina Barber?

  I knew it, I knew it.

• 3:52Speaker 02

  Like they can pick a cow carcass clean in under 40 minutes.

• 3:56Regina Barber?

  That is super fast.

• 3:57Speaker 02

  Yeah, and rotting flesh is host to all sorts of bacteria, many of which can cause human diseases.

• 4:04Regina Barber?

  And these vultures, they're not getting sick, so what's going on there?

• 4:07Speaker 02

  They're super well-adapted to eating dead meat. One fun fact, their stomach is like 10 times more acidic than ours.

• 4:14Regina Barber?

  This is making my acid reflux look like, like, nothing.

• 4:18Speaker 02

  Yeah, yeah. I spoke to Anant Sudarsan, an environmental economist at the University of Warwick, who studied the fallout of this mass die-off. Here's what he had to say.

• 4:27Speaker 04

  What happens to these carcasses if vultures are not removing them? And at least in India, a lot of them will end up in water bodies because that's one easy way to dispose of them.

• 4:38Speaker 02

  As a result, waterborne pathogens like coliform bacteria can become a bigger problem. Anant and his colleagues analyzed mortality data from the country and found it ticked up 4% because vultures disappeared. That's a lot and translates to about 100,000 additional deaths a year.

• 4:55Regina Barber?

  I mean, it does sound like these vultures are essential for like sanitizing the environment.

• 5:01Speaker 02

  Yeah, and their absence had another crucial effect. All that extra meat ended up becoming food for feral dogs, which spiked in number.

• 5:09Regina Barber?

  Oh, wow.

• 5:10Speaker 02

  Here's Chinmei Sonawan, a biology grad student at Stanford.

• 5:13Speaker 05

  Millions more feral dogs, millions of more people being bitten by these dogs. And it's estimated something like 50,000 additional people were dying from rabies as a result of these cascading interactions.

• 5:32Regina Barber?

  Rabies? I mean, that's very, very scary. Okay, so this decline of vultures sets off this series of dominoes that like ultimately results in more people dying.

• 5:42Speaker 02

  Yeah, and to Chinmei, the story of these vultures really exemplifies the huge, but often hidden benefits that scavengers provide.

• 5:51Regina Barber?

  So I'm guessing other scavengers are doing maybe the same thing?

• 5:55Speaker 02

  For sure. Chinmei told me there's been a burst of studies looking at the relationship between human health and scavengers in the past few years.

• 6:02Regina Barber?

  So what other scavengers have actually been studied?

• 6:05Speaker 02

  So one study estimates that hyenas scarfing up cattle carcasses outside of one of the largest cities in Ethiopia prevents five cases of anthrax and bovine tuberculosis each year.

• 6:16Regina Barber?

  Oh, wow. Okay, hyenas? I mean, they get a bad rap in Lion King, but maybe they're awesome.

• 6:20Speaker 02

  Yeah, yeah. Another study found that civets and other scavengers in Malaysia actually reduce the amount of diarrhea-causing bacteria that build up on flies by quickly eating carrion, so flies have less time to multiply. Flies are a big vector for these kinds of diseases, so reducing the bacteria load on them could lead to fewer people getting sick.

• 6:40Regina Barber?

  Okay, let's back up for a second. What's a civet?

• 6:42Speaker 02

  They're kind of cat-like, but also like a long-legged weasel. Google them after this.

• 6:47Regina Barber?

  Okay.

• 6:48Speaker 02

  And turtles in Australia eating carrion was associated with improvements in water quality in wetlands. The list really goes on and on, but there's one big problem.

• 6:57Regina Barber?

  Oh, yeah? What's that?

• 6:59Speaker 02

  Yeah, like I mentioned, many of these species are declining. Chin May and his colleagues published a big analysis of all this work in the journal PNAS in June, looking for broader patterns on how scavenging species influence health and also how those scavenging species are doing. They looked at over 1,300 species and found that up to 36% are declining or threatened with extinction.

• 7:22Regina Barber?

  Oof, that is a lot. Why?

• 7:24Speaker 02

  Yeah, it's a combination of habitat loss, hunting, and the wildlife trade.

• 7:28Regina Barber?

  Yeah.

• 7:29Speaker 02

  But they found that not all scavengers were equally at risk. The biggest, most specialized scavengers, things like vultures or hyenas, were more likely to be threatened.

• 7:39Regina Barber?

  Wow.

• 7:39Speaker 05

  When we lose these large wildlife, smaller wildlife tend to replace them.

• 7:45Regina Barber?

  Okay, what kind of smaller wildlife is he talking about?

• 7:48Speaker 02

  Smaller or less specialized scavengers, who sometimes eat carrion, but can eat other things, too. Think things like rats or mice, or in India, feral dogs.

• 7:57Regina Barber?

  Okay, but if those, like, smaller scavengers are still eating carcasses, wouldn't they maybe sub in for these other scavengers?

• 8:05Speaker 02

  Chin May actually thought that going into his study, but he and his colleagues ended up finding that these smaller scavengers just aren't as good at scavenging as what they call apex scavengers.

• 8:16Regina Barber?

  Okay, apex scavengers. This is like the great white sharks of eating dead stuff, and these smaller ones just can't keep up.

• 8:23Speaker 02

  Yeah, exactly.

• 8:24Regina Barber?

  Okay.

• 8:24Speaker 02

  Here's Chin May again.

• 8:25Speaker 05

  Therefore, there's more carcass waste, therefore, more pathogens in the environment, and then therefore, people are more likely to pick up. Disease from these sources.

• 8:35Regina Barber?

  Right. I mean, that logic makes sense.

• 8:37Speaker 02

  Yeah, and smaller scavengers like rats or dogs are more likely to carry pathogens themselves. Plus, humans are a lot more likely to come into close contact with those than, say, a vulture.

• 8:48Regina Barber?

  So in the end, what does this all add up to?

• 8:52Speaker 02

  Chinmay says basically that a world with fewer apex scavengers is one that could make humans sicker. Other researchers I spoke to agreed. Here's Christopher O'Brien, a biologist at Maastricht University.

• 9:04Speaker 06

  The take home message is that we need to be always factoring in nature into the equation of human health, human suffering, human well-being in general, and we can't ignore it.

• 9:20Regina Barber?

  So what's being done and like, what can be done to help these scavengers?

• 9:25Speaker 02

  Conservation, basically.

• 9:26Regina Barber?

  Yeah.

• 9:26Speaker 02

  Chinmay and his colleagues argue that taking steps to conserve top scavengers by protecting their habitat or restricting their hunting could help preserve some of the benefits they provide. But what happened to India's vultures offers a cautionary tale of sorts.

• 9:40Regina Barber?

  What's going on right now with those vultures?

• 9:43Speaker 02

  Yeah, so the Indian government banned the use of that toxic painkiller by veterinarians in 2006.

• 9:49Regina Barber?

  Okay.

• 9:50Speaker 02

  But the vultures are still struggling to get back to anything close to their old numbers.

• 9:54Regina Barber?

  That is very devastating.

• 9:57Speaker 02

  Yeah, and this all just shows how dependent our collective health is on the natural world, and parts of it that we often ignore. And it shows how widening our sense of what we can do to improve health, to include something as seemingly random as protecting animals that are really good at eating dead stuff, could lead to a healthier planet for everyone, us included.

• 10:20Regina Barber?

  John, thank you for, you know, reinforcing my love for scavengers, actually.

• 10:25Speaker 02

  Happy to do it.

• 10:27Regina Barber?

  Short wavers, if you like our show, do us a favor and share it with one friend. It helps us grow and sustain our show. We appreciate you. This episode was produced by Burley McCoy and edited by our showrunner Rebecca Ramirez. Tyler Jones checked the facts. Jimmy Keely was the audio engineer. Beth Donovan is our senior director, and Colin Campbell is our senior vice president of podcasting strategy. I'm Regina Barber.

• 10:50Speaker 02

  And I'm Jonathan Lambert.

• 10:51Regina Barber?

  Thank you for listening to Short Wave from NPR.

• 11:05Speaker 00

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