Scarfing down their food  *whole* keeps barn owls moving.

After all, these hungry birds gotta eat and  there are lots of little rodents to hunt.

Barn owls need a hole to nest in, and when a  tree isn’t available, they’ll use a building … … or an owl box, like this one  in California’s Napa Valley.

Scientists keep tabs on the owls inside.

Winegrowers invite barn owls to raise   their young in the boxes because  owls are pest control machines.

I mean, a barn owl family can  kill about 3,500 varmints a year.

They don’t take ’em all out,  but they can make a dent.

They particularly like gophers,  like this stunner right here.

Their constant tunneling damages  roots and irrigation lines.

And then there’s voles,  which gnaw on the grapevines.

This 2-week-old owl already has the hang of it.

But how the heck does it keep down all that food?

Well, it doesn’t.

Meet the owl pellet.

Check out this furball.

And here’s a jaw.

Gnarly!

The secret to turning this into this  is its stomach.

It has two chambers.

The first one oozes digestive  juices, like our stomach.

The second one – the gizzard – squeezes  the remains with powerful muscles.

The fats and proteins get absorbed.

The  fur and bones become tightly compacted.

After about eight hours in the gizzard,  the result is one of these beauties.

For researchers like Laura Echávez, from Cal  Poly Humboldt, pellets are forensic evidence.

She carefully dissects them to find out how many  pesky gophers and voles the owls took care of.

Laura (off camera): The tail still has skin on it.

This unlucky rodent had a small  skull.

It could be a vole.

But then she examines the teeth.

Laura (off camera): The teeth are   actually looking more like a gopher’s.

They’re kind of circular, surrounded  by a white ring of enamel.

And the first and second teeth are joined  by a bridge.

Classic gopher trademarks.

Laura (off camera): If it’s a gopher, it’s a very  young one, because this is on the small side.

Sometimes more than one carcass  is crammed into a single pellet.

This one had two gophers.

Winegrowers love barn owls  for their prolific appetites.

But researchers still don’t know whether vineyards  are an ideal place to raise an owl family.

Christian Cortez, a researcher  at Cal Poly Humboldt,   studies young owls to see  how well they’re growing.

After covering their head to calm  them down, he takes a drop of blood,   and plucks a feather.

They will tell him  if the owlet is getting enough to eat.

Researchers want to know, do owls  have enough open space to hunt in?

And do the toxic chemicals Napa  winegrowers sometimes use to kill rodents   end up hurting the owls too?