Four decades after the United States banned a pesticide harmful to bald eagles, the patriotic bird's population is finally thriving.

Urban sprawl and deadly pesticides like DDT nearly destroyed the bald eagle population in the lower 48 states, according to NBC News. By the mid-1960s, only 450 nesting pairs were left in the continental U.S. But now the majestic birds are returning to the country that prizes them, and not just in the rural wild. Nests are popping up in cities as urban as Chicago, which hasn't had a bald eagle nest in 100 years.

"DDT was a really big problem for the bald eagle," Megan Ross of Chicago’s Lincoln Park Zoo told NBC News. "Bald eagles in particular were not able to form appropriate shells, and so when they weren’t able to reproduce, their numbers really plummeted."

But since DDT was banned in 1972, the birds that once faced extinction are making a comeback. There are now more than 9,000 nesting pairs of bald eagles in a country that's proud to have them back.

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