Many schools and businesses will be closed Monday for an unofficial holiday in Pennsylvania, the start of deer season at sunrise.

The first day of deer season is typically the most hunted day of the year in Pennsylvania; about 750,000 hunters fan out in the woods and fields, according to the state Game Commission.

Coming up with a figure for the statewide deer herd population proves more tricky, according to spokesman Travis Lau.

Commission biologists pin hefty caveats to such estimates, he said.

"They are an imaginary number," Lau said. "They are compiled from harvest estimates that are created by a formula because we know only about 60 percent of hunters report their harvests."

Statewide, the deer population looks to be stable or growing, except in the area around Pittsburgh.

Between 50 and 60 percent of the deer killed throughout the two-week season are expected to be taken on opening day.

"It’s the most heavily hunted day of the year," Lau said. "Hunters putting pressure on deer amount to greater deer sightings, more deer sightings throughout the day, more deer harvested throughout the day. It’s an opportunity that most deer hunters wouldn’t trade anything to miss."