GEOFF BENNETT: Finally tonight, we take a closer look at one of America's most revered symbols.

Despite centuries on the national seal and widespread assumption, the bald eagle has never officially been designated as the U.S. national bird.

Our John Yang has this report on the effort to change that and why it matters.

JOHN YANG: Along the Mississippi River, about 80 miles south of Minneapolis, a bald eagle glides high above the water, searching for prey.

This area is home to more than 50 nesting pairs of bald eagles, one of the highest concentrations in the country.

It's why tiny Wabasha, Minnesota, is called the Eagle Capital of America.

SCOTT MEHUS, Director of Education, National Eagle Center: Who cannot love that big, massive beak, the bright plumage, the yellow feet, the black talons?

It's just awe-inspiring.

JOHN YANG: Scott Mehus the education director at the recently renovated National Eagle Center in the heart of Wabasha, 15,000 square feet entirely dedicated to this stately creature.

SCOTT MEHUS: Everybody has a story when we're here at the Eagle Center.

They want to come and share that story.

JOHN YANG: People can learn all about the eagle, from its size, diet, and habitat to its central place in American history and culture.

A trove of the center's eagle memorabilia was donated by retired real estate investor Preston Cook.

PRESTON COOK, American Eagle Collection: I was asking an ornithologist friend of mine from Canada what he sees when he sees an eagle, and he says: "I see an eagle."

But when an American sees an eagle, we see something a little bit different.

We see the freedom, the liberty, the independence, the power.

We see all of those things in this bird that represents America so often.

JOHN YANG: Cook is perhaps the world's foremost collector of eagle-related items.

PRESTON COOK: Obsession is probably a good word for what I have done.

And then I have got the buttons.

JOHN YANG: It began with the brass buttons that adorned his military uniform as a young man.

Now his collection has more than 40,000 items, filling floor-to-ceiling shelves next door to the center.

PRESTON COOK: I never tire of looking for eagles or watching eagles.

I pull my car over when I'm driving around this area when I see an eagle.

I'm in awe continually.

JOHN YANG: Around 2010, as Cook was doing research for his book "American Eagle," he tried to nail down exactly when it became the U.S. national bird and found out that it wasn't.

Research at the National Archives confirmed his finding.

The Second Continental Congress put the bald eagle on the national seal in 1782, but there had never been a law or an executive action designating it as the national bird.

So Cook drafted legislation to do just that.

He took it to Minnesota Senator Amy Klobuchar and Representative Brad Finstad, whose district includes Wabasha.

PRESTON COOK: It does matter.

It gives it a little higher status.

This assumption has been with us for 240-some-odd years.

JOHN YANG: The Senate passed the bill without opposition.

If it's approved by the lame-duck House and President Biden signs it, the eagle would join the rose, America's national flower, the oak, the national tree, and the bison, the national mammal.

PRESTON COOK: The eagle has two wings.

It has a left wing and it has a right wing, and it has a body middle.

And so it really represents all Americans.

JOHN YANG: The Eagle Center's Scott Mehus says it's important to keep educating America about it soon-to-be-official bird.

SCOTT MEHUS: It's just an opportunity for people to be aware of this bird that still needs its recognition.

I think that's the cool part, is that people are able to come here and to recognize that this little small town in Minnesota has that opportunity to do something major, really to set the world straight that the bald eagle, yes, is our nation's symbol, but it was not designated as our nation's bird.

JOHN YANG: Until now.

For the "PBS News Hour," I'm John Yang.