[suspenseful music] - [Narrator] What do opossums, Key Largo woodrats, and dumpster-diving cats have in common?

Burmese pythons, of course.

That's right, pythons.

- Unfortunately, my work went from studying mammals to mostly studying pythons.

- [Narrator] Because these pythons are eating all three of these mammals.

That's devastating the South Florida ecosystem, and that's a serious problem.

- [Mike] And how to detect them, find them, manage them, to prevent the extinction of these endangered rodents, and largely mammals across the Florida Keys.

- [Narrator] Mike Cove is the curator of mammals at the North Carolina Museum of Natural Sciences.

He studies the delicate balance of ecosystems, and the impact of invasive species.

- I don't love pythons.

I have a respect for pythons, and think they're fascinating animals.

Unfortunately, they don't belong in the United States.

- But before we go any further, let's go back to the start of Cove's research.

It's an 11-mile stretch of the Crocodile Lake National Wildlife Refuge in Key Largo, Florida.

Cove was studying two endangered rodents for his dissertation in 2012, the cotton mouse and the Key Largo woodrat.

So Mike, you track pythons, but from the looks of it here, it didn't really start out that way.

Can you tell us a little bit about that?

- Yeah, yeah, yeah.

So I've been working in the Florida Keys for 10 years now.

And I started in the Florida Keys with this species here.

This is the Key Largo woodrat.

This is an endemic rodent.

It only lives on the island of Key Largo.

The typical ecosystem engineer is the beaver, right?

They build large dams.

Well, these small woodrats also build large stick nests.

This small rodent is carrying sticks, sometimes two, three feet long as far as 50 yards to pile them onto these giant stick nests, and provide all types of ecosystem services, because they're basically creating giant compost heaps that help restore the soil and create habitat for lots of other animals that also live inside the nests with them.

- [Narrator] But their population was declining and Cove needed to figure out why.

He started to look at feral cats that came into the area from neighborhoods nearby.

Note that these cats are technically an invasive species, spread by humans.

The cats were already dumpster diving, and getting fed by sympathetic people.

And Cove saw that the possums and raccoons were taking advantage of that extra food source as well, then going back into the forest.

More food meant they would multiply and disrupt the woodrat habitat, but he saw other dangers as well.

- [Mike] Yeah, so we started tracking possums and raccoons to evaluate how much time they were spending in the wildlife reserves versus outside, gaining external resources from eating cat food.

But in doing that we were also looking at potential disease spread from cats to raccoons to ultimately affect the rodents.

- [Narrator] Look to the right of your screen and you'll see all that led him to something that definitely didn't belong and was yet another threat to the ecosystem, Burmese pythons, which is considered an invasive species as well.

- [Mike] Secretly, we knew that the python population was growing and you know, I've always kind of thought, man, wouldn't it be wild if one of these got eaten by a python?

And it led us to this homing beacon with this animal inside the python's stomach.

- [Narrator] It took a full month to realize their first tracked opossum had been eaten by a python, then they had to go get it.

- [Mike] The Florida Keys are a big fossilized coral reef, right, so there's tons of places for them to hide.

- [Researcher] He totally just peed, didn't he?

- [Mike] So on average, it takes three to four full grown humans several hours to pull a python out of the ground.

These things are pure muscle.

- [Narrator] But just like that, Cove had discovered a way to track them.

So what's an invasive species?

Enter the pythons, snakes that were never part of the natural plan and have taken over South Florida, particularly in the Everglades National Park and into the south and Key Largo.

- [Researcher] Wow.

- [Narrator] The pythons are devastating the ecosystem.

- [Mike] In the Everglades, it's almost a mammal desert.

There's basically no mammals left.

- [Narrator] Where did these pythons come from?

According to the Nature Conservancy, the first Burmese python was found in 1979, and it was likely a former pet, which was released or escaped.

And since then, they've multiplied, and they might be moving northward.

- [Mike] The climate models and the habitat suitability models suggest that they could make it all the way up into North Carolina without any type of, you know, increasing warming of the climate or anything like that.

They could exist and persist in North Carolina right now if they were able to establish.

- [Narrator] The state of Florida has efforts underway to reduce the python population that even include contests for cash money.

Meanwhile, Cove says it's ironic they're trying to get rid of the pythons, but says there's little choice.

- You know, the sad reality is these Burmese pythons are rare and endangered in a lot of their endemic native range in Southeast Asia.

But their sad reality is just because they're common here doesn't mean that we can celebrate that.

That this is, you know, a backup population for this endangered species.