This is a passenger announcement. You can now book your train on Uber and get 10% back in credits to spend on Uber eats.

So you can order your own fries instead of eating everyone else's.

Trains, now on Uber. T's and C's apply. Check the Uber app.

This is scientific Americans 60 second science. I'm Jason Goldman.

We literally get down on our hands and knees and start slowly sifting through the leaf litter looking for bits of hair or a little chunk of bone.

Tom Gable is tracking a predator. In fact, he's tracking a whole pack of him.

Oh it's very much like a crime scene investigation.

Since 2015, the University of Minnesota Conservation Biologist has used GPS collars to track 30 wolves inside Voyager's National Park.

Those collars led Gable and his team to kill sites.

And there, amid the leaf litter, were bloodied bits of fur and bone.

Clues about how wolves alter the ecosystems they live and hunt and kill in.

The long-term study is, in a way, a quest to broaden a science story that goes back 25 years.

For wildlife ecologists, the story of the reintroduction of wolves to the Greater

Yellowstone Ecosystem on January 12, 1995 has become canonical.

The story goes something like this.

As the elk grew to fear the wolves, they changed where and how they foraged. That gave willows, cottonwoods, and

aspens a better chance to grow near streams. It also meant more riverside berries for foraging grizzly bears, and it led to alterations in the flow of those streams, sending water in new directions.

Wolves outcompete coyotes for access to prey, so coyote populations plummeted, which led to a rise in fox,

rabbit, and ground-nesting bird numbers, and so on.

Ecologists called this row of biological dominoes a trophic cascade.

Regardless of your inclination, I think it's hard not to be like, wow, this is amazing, right?

If that is true, that's really incredible.

...