RAPID CITY, S.D. (AP) — Federal authorities in South Dakota are preparing to announce more charges stemming from a two-year undercover investigation into the illegal trafficking of eagle parts.

U.S. Attorney Randy Seiler will hold a news conference in Rapid City on Friday to announce several new indictments and 16 new defendants.

Prosecutors announced indictments against 15 people in April for illegally trafficking in eagles and other migratory birds.

The case 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.

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.