Authorities are investigating the deaths of 13 bald eagles discovered on a Maryland farm in the state's largest die-off of the national bird in 30 years, officials said on Monday.

Maryland Natural Resources police received a call on Saturday from a man reporting four dead eagles near Federalsburg in the eastern part of the state, said spokeswoman Candy Thomson. Officers arrived and discovered nine more dead birds nearby.

Catherine Hibbard, a spokeswoman for the U.S. Fish and Wildlife Service, which is investigating the deaths, said the cause of death was unknown pending a medical examination.

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The maximum fine for harming a bald eagle is $100,000 and up to one year in prison, she said.

The bald eagle, which almost disappeared from the United States decades ago, was removed from the federal endangered species list in August 2007 after the banning of the pesticide DDT and habitat protection led to its recovery, according to the U.S. Fish and Wildlife Service.

The bald eagle is a symbol of the federal government and is featured in the presidential seal and on U.S. currency. The bird is federally protected.

Thomson said the 13 birds represented Maryland's largest bald eagle die-off in 30 years.