[playful music] - [Narrator] Meet the weasel.

Mysterious, hard to find, kind of sneaky.

They are all traits that give the word weasel a bad name, when it's applied to a person.

- [Roland] I really like weasels.

And in my career I've caught them a couple times on camera, but not very often, it's like really lucky and have seen them in the wild only like twice.

And so they're kind of mysterious.

- [Narrator] But in the wild, those same traits help the world's smallest carnivore survive.

- The other thing with weasels is they're always like in the nooks and crannies, right?

Their whole body design is about going into a hole after a mouse.

- This is the skull of a long-tailed weasel.

I brought it 'cause it really shows one of the adaptations that the weasel has made in its morphology, it's, the shape of its body to be a pure carnivore and that is elongated head, you know, really sharp teeth really helps to not only navigate the landscape very quickly, move very quickly.

- And we started to wonder how are they really doing?

Like how is their population doing?

Are they just like so hard to see because they're so sneaky?

Or are they actually rare and even possibly declining?

[playful music] - [Narrator] Two species of weasel call North Carolina home.

The long-tailed weasel is about eight inches long.

It weighs about an ounce.

It's found throughout the state.

The least weasel, as the name suggests, is a bit smaller.

It's only found in the mountains.

In general, weasels may be small in stature but they play a big role in the ecosystem.

- They help control prey populations, such as mice, you know, kind of rodent populations that maybe folks view as undesirable.

Well, guess what?

Your weasel can help manage those populations.

The other reasons we should get a better idea of what's going on with the weasel population is if they are in decline, that's probably indicative of other things going wrong in the ecosystem.

[pensive music] - [Narrator] And that's the problem.

Scientists don't know how the weasel population is doing.

The data suggest weasels may be in trouble.

- We're seeing some patterns that there are places in the country that used to have a lot of weasel records and now don't seem to have very many.

And one of the things we see is some of the hotter areas in the southeast used to have a lot of long-tailed weasels and now they don't have as much.

So that suggests maybe it's climate change, maybe the temperature has risen too much and it's not good weasel habitat.

In North Carolina here, we still have them in the mountains where it's a lot cooler, and we have a lot less of them it seems like in the Piedmont coastal plain.

So we're thinking could be climate, but there's other things going on there, right?

There's also more habitat conversion.

More forest has turned to fields.

- [Narrator] But before researchers can say whether the weasel population is stable, growing or declining, scientists need a baseline of data to start with.

So you could say this story is also about building a better weasel trap.

- The trick is when you don't see something you don't know is it because it's hard to see or because it's not there.

And so one of the things we're trying to do now is figure out a better way to survey for weasels.

- [Narrator] Scientists are testing specialized camera traps.

- And we open up our Mostela box and we have our camera on one end and our tube on the other.

So it's basically a PVC tube that has a opening cut out of it.

And what this Mostela box is doing is it's serving as both a visual attractant, because with the leaf litter and this opening, a weasel will hopefully think, "Oh this is a nice burrow and maybe there's a mouse inside."

And hopefully what's further gonna track this weasel to go into this opening is we usually put bait.

And while it comes in, it slows down hopefully long enough that we get a great picture to identify it.

- We're gonna subject you to an experiment here just like we do the weasels.

- [Narrator] They are also testing different baits to draw weasels to the traps.

- Sweetmeat predator baits.

Give that a good whiff.

- Oh, oh, okay.

If I'm a weasel, I'm probably gonna go to that one.

I want that.

- Here we go.

- It's also the weasel doesn't weasel out of the research.

This looks like a perfect trap, why here?

- Why here is because as I was walking through the woods again, trying to get into the mindset of what is a weasel looking for.

We look for fallen branches and trees that weasels like to hop on and travel along.

We look for rock cavities.

Rock cavities, not only do weasels use kind of to travel upon, but they're gonna poke into that rock cavity the various crevices to see if there's any of their prey species, such as mice.

[inspiring music] - [Roland] Are going to places that we think are good weasel habitat, lots of cover, lots of rocks.

And when we set the cameras, instead of just putting them out on a tree, we're putting out different set lures and different baits to see, okay which are they gonna hit first?

Which are they gonna spend their most time at?

And then that will be become in the future our go-to method for surveying for the weasels.

Likely, whatever the problems are that are causing weasels to decline, if they are declining, are probably affecting other species as well.

And so getting to understand the problems that one species is having can help you improve the ecosystem for a lot of different angles.

[inspiring music]