Ducks and shorebirds with broken wings, smashed skulls and other signs of internal bleeding were found on the shores around Big Lake Wildlife Management Area in Molt, Mont., authorities said.

Biologists who surveyed the area estimated that between 11,000 and 13,000 birds were found dead or badly injured after the hailstorm.

Most of the wounded birds are not expected to survive. About 20 to 30 percent of the entire bird population at the lake died in the storm, according to FWP wildlife biologist Justin Paugh.

Local weather reports said the towns of Molt and Rapelje, both located near the wildlife management area, received two inches of hail in conditions of 70 mph winds, the press release said. The hailstorm reportedly flattened crops, shattered windows and damaged roofs and vehicles in the area.

Big Lake Wildlife Management Area’s lake and surrounding wetlands serve as the nesting areas for dozens of species of ducks, Canada geese, double-crested cormorants, shorebirds, gulls, pelicans and other waterfowl, the agency said. Officials will continue to monitor for signs of diseases, including botulism, which is caused by rotting carcasses, in order to protect the surviving bird population.