Federal authorities in South Dakota announced indictments Friday against 16 more defendants in a two-year undercover investigation into the illegal trafficking of eagle parts. They also said more charges are possible.

The new charges came on top of indictments that U.S. Attorney Randy Seiler announced against 15 people in April for illegally trafficking in eagles and other migratory birds. The new defendants include operators of pawn shops in Rapid City and Mobridge and a trading post in Buffalo Gap, two pawn shops, and other individuals from South Dakota, North Dakota, Nebraska and Idaho.

The investigation, dubbed project Dakota Flyer, offers a rare window into the black market for eagle carcasses, feathers, parts and handicrafts. Eagle heads or wings can fetch hundreds of dollars. The parts are often used in Native American-style handicrafts.

Not only are eagles the national symbol of the United States, they're widely considered sacred by Native Americans. Federal law limits possession of eagle feathers and other parts to enrolled members of federally recognized tribeswho use them in religious practices. Hunting them generally remains illegal.

Seiler said the investigation targeted only the illegal trade. He said it never targeted Native Americans who use lawfully obtained feathers for religious and cultural purposes.

The original indictments portrayed an illicit trade carried out through face-to-face meetings, emails, texts and personal introductions.

On Friday, Seiler told The Associated Press that investigators used DNA to determine that parts from more than 240 bald and golden eagles and around 150 hawks and owls were unlawfully trafficked by the defendants. He said prosecutors will seek $10,000 in restitution for each eagle for a total of $2.4 million.

"The extensiveness of the market, and the amount of the market and the number of individuals I think surprised even us in terms of how prevalent this practice was in South Dakota," he said.

The investigation has also generated intelligence about illegal parts-trafficking outside of South Dakota, in western and southwestern states, that Seiler said could lead to charges in those states as well.

The new charges are for alleged violations of federal laws against illegal trafficking in eagles, migratory birds and other wildlife between 2013 and 2017. They're a mix of felony counts with two- or five-year maximum sentences and fines of up to $250,000, and misdemeanors punishable by up to a year in custody and fines up to $100,000.

The new defendants are due in court Oct. 6 in Pierre, Oct. 11 in Rapid City and Oct. 12 in Aberdeen. Seiler said all of them have been served with summonses.

The original defendants included people from Iowa, Nebraska, South Dakota and Wyoming. Seiler said all received summonses except for one who was arrested in New York state and is being returned to South Dakota.

They all have trial dates and discussions with them are underway that could produce information that leads to additional charges.