The U.S. Department of Justice has threatened criminal action against the state Department of Transportation over Oahu’s lights and the protection of seabirds.

In December, the department notified Hawaii transportation officials of a multiyear investigation of lights "that are allegedly causing unlawful take of protected bird, turtle and moth species under the Migratory Bird Treaty Act and Endangered Species Act," according to a January letter by state Deputy Attorney General Laura Kim.

Although the Justice Department inquiry is statewide, the focus is chiefly on Oahu, where a considerable number of wedge-tailed shearwaters are suspected of being injured because of DOT lighting, Kim said in the letter.

Wedge-tailed shearwaters, the only seabirds nesting on or around the main Hawaiian Islands, are not endangered but are protected under the Migratory Bird Treaty Act.

The Transportation Department learned in December of potential federal legal action and that the state has the option of either entering into an "plea agreement" or face a "criminal trial," according to Kim in the letter. The Attorney General’s Office hired legal firm Bingham McCutchen LLP to assist with the case.

Anne Lopez, spokeswoman for the state attorney general, said there have been no indictments filed, but declined to comment further because of the ongoing investigation.

The Justice Department could not be reached for comment.

Caroline Sluyter, DOT spokeswoman, said she couldn’t comment on any pending litigation.

Fledgling seabirds can become disoriented by bright street and ballpark lighting. Young birds use the moon and stars to navigate their way to sea from nesting grounds, and the lights can interfere with their flight.

Instead of heading out to sea, they become confused and temporarily blinded by lights as they are drawn toward land. They then fall to the ground, where they are vulnerable to cats, dogs, mongooses and cars.

Since 2007, state crews have been replacing fixtures in streetlights with lenses that have downward lighting features. About 1,800 of 11,000 lighting fixtures were replaced in areas that include Ala Moana Boulevard, Nimitz Highway, and the H-1 and H-3 freeways. Costs for each lighting fixture range from $250 to $400.

The Justice Department’s case against the Department of Transportation is similar to two separate cases in 2010 against Kauai County and the Kauai Island Utility Cooperative over lighting that affected endangered Newell’s shearwaters and Laysan albatross.

Both cases resulted in plea agreements for violating the Migratory Bird Treaty Act.

Under those agreements, Kauai County paid a $15,000 fine and was required to implement corrective measures during a probation period.

The Kauai Island Utility Cooperative also paid fines totaling $40,000 for violating the Endangered Species and Migratory Bird Treaty acts.

The electric utility provider also accepted an 18-month probation period to take corrective measures that included reconfiguration of power lines and the planting of trees to shield lights from seabirds.

The lighting at stadiums on Kauai for Friday night football prompted a move to Saturday afternoon football.