I am NOT a cat person, but I gotta say, cats  are kinda crushing it out there.

All over the world,   cat populations continue to grow while most  wild predators are in steep decline.

Apart from dogs, cats are the most  abundant predatory mammals the world   has ever seen.

There are between 600 million  and a BILLION domestic cats in the world.

But here’s the thing: we actually have no idea  what cats are doing when we are not around.

Which is a pretty typical cat thing, right?

So I met up with some scientists conducting not   only the biggest study of cat movement  in the world, but the largest tracking   study of any species - to find out what  exactly cats are doing out there.

I’m Shane Campbell-Staton, and  this is Human Footprint.

You actually own cats.

I– We have four cats here in the house.

I'm not sure own is the proper verb.

Okay, hahaha.

But they live here.

And they run  the show, put it that way.

In the biology world, Jonathan is a  legend for his research on lizards.

But outside the lab, cats are his passion.

I’ve always been into cats, but it never occurred   to me to do anything professionally with  them, because they’re just cats!

But he just couldn’t help himself.

And now, he’s  written a whole book on the science of cats.

So how do we get from the truly wild cat to these  guys that are running around your house?

The idea is this: that when humans  adopted an agricultural lifestyle,   we started raising crops and storing them; and  that of course attracted rodents, and this was in   the native range of the African Wild Cat.

These wild cats started hanging around human   settlements.

The less afraid of us they  were, the better they did.

Over time,   cats evolved to be friendlier, or at  least more tolerant of human company.

We started appreciating them too, and soon, we  were bringing them with us around the world.

Let me see one of these cats.

All right.

I'll go get one right   here.

He's in his little basket over  here.

It's showtime, Nelson.

This is Nelson.

He's the one on your mug.

Let me see what all this noise is about.

Now if I look uncomfortable here,   it’s because I'm very allergic to cats.

A key phase in domestication, in general, is when   humans take over the breeding process.

Cats became semi-domestic simply by hanging   around and catching mice.

It’s only for the  last few hundred years that we've controlled   who mated with whom, producing dozens of distinct  breeds…like the American Burmese in my lap.

Here you go Nelson, I’ll put  you back in your basket.

I know I'm going to pay for that later.

So you mentioned that a couple of your cats   are inside/outside cats.

When they're out  cruising, do you have any idea what they're   doing out there?

Well, mostly no.

He says, "None of your business  is what I'm doing out there."

Cats would be appalled to know  that researchers are working hard   to uncover their secret lives outdoors.

Roland Kays knows more about animal tracking   than almost anyone on the planet.

What he gets  up to in his own time… that’s his business.

Hey, welcome.

Hey, how's it going?

Thank the good Lord for antihistamines.

‘Cause this was not in my contract.

Is this not the perfect place  to talk about cats?

There's definitely a lot of cats in here.

It's a cat coffee shop.

And if you want to, you   can walk out of here with your very own cat.

Okay.

I… will pass, but I   appreciate the sentiment.

You know you’ve got too many cats   when you start giving them away for free.

When cats go out, cats hunt, right?

I mean this   is why we domesticated them in the first place.

One cat catching a few things isn't a big deal,   it's when you magnify that by 600 million, then  all of a sudden, maybe it is a big deal…   The problem is, scientists know next to  nothing about what cats do in the wild,   or what their impact might be.

Roland’s answer?

Track cats the way   we track wild predators – by fitting  them with GPS-enabled collars.

Several of those cats were right here in  Raleigh, including a cat named Kraken.

Hello.

Hey, how are you?

Good, how are you?

Come on in.

So she came to us as a stray in the summer,  before we decided to … bring her inside.

Is it like a mystery to you what  her life is like out there?

Oh, yeah.

Absolutely.

I found out about  Mohammed's study, and so we signed her up.

So this is the tracker that we are using on the  cats.

What we have here is the microchip that has   both the accelerometer and the GPS.

The accelerometer measures the cat's   movement - left-right, forward-reverse.

And the GPS tells us where the cat is.

We save the data on the collar, then we retrieve  it from the animal.

Then connect it to a   computer to download the saved data here.

So a cat has to bring you the data back?

Yeah.

With this study,   what will we know about the lives of these  cats that we didn't know before?

Well, one of the things that we're hoping the  more detailed data will show us is, where exactly   they're going and what habitats they're using, how  often they're crossing streets, for example.

And if they're going into the natural areas  where they might on one hand encounter a coyote   or something scary, but also could potentially  be hunting native species that would be more   concerned about out in a more natural area than  compared to the more neighborhood urban area.

So understanding exactly where the cats  go and also what their behavior is.

Cool.

So should we release the Kraken?

I'm so glad I got to say that.

I think this is Kraken right here… It went down here to this house,   and then it came back, and you can see one trek  way over there.

That was a bit of a surprise.

Roland’s study isn’t just the biggest study of  cat movement in the world - it's the largest   tracking study of any species.

Roland sent GPS  collars to collaborators all over the world.

So this is just a map of the  earth, and I've got pink dots   anywhere that we were tracking cats.

So, we've got Allie, Aley, Amber Rose,   Amelia, just A to Z probably we've  got all kinds of different ones.

It turns out, most cats don’t  stray too far from home.

Our average across all 900  cats was 3.5 hectares.

That’s about six or seven football fields.

The next thing we had to figure out is,   how do we put that into perspective?

Roland compared data from domestic cats   to their closest wild relatives.

What we found was that the domestic cats   have a four to ten times more ecological  impact on their prey than do wild species,   but that's going to be concentrated within  basically 100 meters of someone's house.

One of their biggest footprints can be  seen on migrating bird populations.

There are some estimates in the United States  that cats kill sort of one to three billion   birds a year.

Billion.

Yes.

But it’s even more small mammals.

It’s like 7-10 billion small mammals.

And the impacts of cats in places  like Australia, New Zealand,   and oceanic islands have been devastating.

There are examples of animals that have been   completely hunted to extinction by cats.

Some biologists consider them the worst invasive   species alive.

But Roland’s got a plan to curb the  impact of these cuddly killers.

It could start by   adding an accelerometer to our cats’ collars.

The accelerometer basically measures the   orientation and the movement of the  collar in three dimensions.

So now, here's the three axes, X, Y,  and Z axis, and you can see they're   very flat.

That means the animal's resting.

So here, you can see, see how rhythmic this is.

Choo-choo-choo-choo-choo-choo-choo-choo-choo.

So that's a walking or running cat.

If the accelerometer can recognize a walking  or running cat, what else can it tell us?

And so what our goal is, is to get artificial  intelligence algorithms on the collar recognizing,   this cat's about to hunt.

One of the amazing things,   so birds have alarm calls, and they listen  to each other.

So they know, like a chickadee   knows the alarm call of the titmouse.

So we could have basically a bird alarm call   go off on the cat's collars and all the birds  would be alerted, "Look out, predator here."

It seems an ingenious solution, but  the flip side is that also, cats learn.

Is it possible that cats will just  learn to hunt a different way?

I'd say it's highly possible that I  would be outsmarted by a cat, yes.

Because cats learn.

If you give a  cat a bell, it learns how to walk   without triggering the bell.

And so, it’s possible that it could   figure out that when it does a certain thing,  there’s this noise that comes from its collar.

I don’t know.

We'll have to wait and see.

But I guess the difference is that the bell   doesn't have the ability to adapt to the cat.

Exactly.

Exactly.

But an AI potentially has the ability to  adapt and learn along with the cat.

Yup, yeah.

That's brilliant.

That’s really cool.

We’ve made a pact with cats.

Even as they  deplete the natural world around us, they   seem to enrich another part of our lives.

Sure, their modern existence can be pretty   bizarre, and damn do they make my eyes itch… But compared to their wild relatives, one thing’s   for sure: cats are evolutionary winners.

If you want more Human Footprint, you can tune   in to the full length series on the PBS  App or on your local PBS station.