“Trophic cascade” is a very sciency  sounding word for “nature’s domino effect”.

Everything is interconnected, so  when you push one domino over, things start to get messy fast. The bugs eat the grass, the birds eat the  bugs, the snakes eat the birds, and so on.

So if you take away the snakes, the birds  become overpopulated and eat too many bugs. Then there aren’t enough bugs to eat the grass, and the grass ends up taking  over other native plants. See how everything gets thrown out of whack  when you remove just one part of the equation?

There are some fascinating  examples of trophic cascades and the effects they have  on both nature and people. Like this thing that happened  in India several years ago. The vultures there have gone  through some rough times.

And while vultures may not be  everyone’s favorite animal, their disappearance caused a ripple effect and  it has cost the country billions of dollars. [♪ INTRO] Before the 1990s, vultures  in India were doing great! There were millions of them, and they had a respected place  in Hindu mythology and culture. They were also highly revered for  the ecosystem services they provided.

Mainly, being nature’s cleanup crew. Anytime there were animal carcasses  lying around, no need to worry! The vultures would be there soon  enough to take care of it for free!

But suddenly, the birds faced a huge problem. In India, many people live in close proximity to  livestock animals like goats, buffalos, and cows. And when the animals you’re raising  get sick, you give them medicine.

A drug called Diclofenac was  introduced in the mid-90s. It’s a nonsteroidal anti-inflammatory  used to treat livestock for issues like swelling or pain during birth. It was quite healing for cattle, but it turned  out to be extremely toxic for the vultures.

Anytime the clean up crew ate dead livestock  that had recently been dosed with Diclofenac, those birds ended up with a healthy, or I  guess unhealthy, dose of the drug as well. Enough of the drug would send the birds  into renal failure, leading to death. And the dieoff was nothing trivial.

Vulture populations in India declined an  estimated 96-99% between 1992 and 2003. The species most affected  were the long-billed vulture, the slender-billed vulture, and  the oriental white-backed vulture. With a rapid decline of not one,  not two, but THREE vulture species, the clean up crew became severely short staffed!

Suddenly, the streets were littered  with dead animal carcasses, which is an issue on its own, so the government  started funding efforts to clean them up. But dead animals on the side of the road  aren’t just an eyesore that make me sad. When you live in close proximity to so many  carcasses, disease can start to spread.

Carcasses are a breeding  ground for deadly pathogens that cause tuberculosis, brucellosis,  and other zoonotic diseases. As the flesh decays and rots,  those pathogens can infect humans through the water we drink or through contact  with other animals that have eaten it. Like dogs.

When India’s primary scavengers declined, others started to show up in  larger numbers, including dogs. And with more dogs came more dog bites. Feral dog populations are hard to track,  but the number of them in India increased by an estimated 5-7 million individuals  from the early 90s to the early 2000s.

And unfortunately, in India, dogs are one of  the main vectors for the spread of rabies, accounting for up to 96% of cases. Left untreated, rabies will be fatal. Not might… WILL.

ALWAYS. This increase in the spread of diseases  has resulted in tens of thousands of additional human deaths and a huge  financial burden for the government, with rabies alone costing an estimated  $34 billion annually from 1992 to 2006. It’s hard to know exactly what the  total cost of this vulture die-off was.

But looking at the estimated cost of  rabies cases, carcass removal, and conservation efforts, we’re talking more  than $150 billion over the course of 14 years! Now this all looks really bleak. And that’s because it was!

But the situation has begun to improve. Diclofenac, the drug that was the catalyst  for this whole nightmare, was banned in 2006. People with livestock began using a newer,  safer drug called meloxican in its place.

Since then, India’s vulture  populations have stabilized. Conservationists have created captive breeding  programs in an effort to boost the population. And not every individual vulture died.

There are actually a few strongholds of  populations that live farther away from people. Out in the forests, they’re far  from agricultural disturbances and there are plenty of hooved  animals they can chow down on without fear that they’ve  been dosed with Diclofenac. So, while the vultures aren’t entirely out  of the woods yet, and I guess maybe they shouldn’t be since that’s where some of them  live, things are starting to look up for them.

Hopefully lots of these eerie, yet iconic birds will be back to flying circles over  dead animals in the near future. [♪ OUTRO]