A duck went through the windshield of a State Patrol helicopter and struck the co-pilot as it was returning to the Twin Cities from a nighttime mission in southeastern Minnesota, the agency said Thursday.

The co-pilot suffered a "suspected head injury" from the incident about 10:15 p.m. Wednesday, was examined at Regions Hospital in St. Paul and released, the patrol said in a series of tweets.

The helicopter was about 35 miles from landing at St. Paul Airport when the windshield was shattered, said Patrol Sgt. Jesse Grabow, who added that the co-pilot had his helmet on with the shield down.

"The pilot was in control and remained in control of the helicopter, returned and landed," Grabow said. The co-pilot received medical attention from troopers and emergency medical personnel upon landing before he went to Regions, the patrol said.

"Bird strikes happen, [but] most time they are not known until after the return of a flight," Grabow said. "Birds coming through into the aircraft itself are not common."

The flight was in support of law enforcement in Wabasha County, the patrol said, without being more specific.

The patrol said it was assessing the severity of the damage to its Bell 407 helicopter, which is one of nine in the agency's fleet. The patrol also operates four small airplanes.