Hikers, bird watchers and anglers now have another nine acres to explore in the Slippery Rock Creek Natural Area, a nature preserve about 8 miles north of Moraine State Park.

The state purchased the former farm land in Worth, Butler County, from the Wild Waterways Conservancy last week for $75,000. The 8.9 acres adjoin and will be added to the 90-acre nature preserve.

"It's a place where you can hear the birds sing and listen to the stream flow," Moraine State Park Manager Obie Derr said.

The fast pace of development in Butler County makes it important to maintain areas like the nature preserve, he said.

"This new tract will provide a buffer to help keep the area as wild as possible," conservancy trustee Frank Moone said Wednesday.

Slippery Rock Creek Natural Area is south of state Route 108 and east of Interstate 79 and is administered by Moraine State Park employees.

The Wild Waterways Conservancy is an all-volunteer organization that seeks to preserve open space in the Slippery Rock and Connoquenessing Creek watersheds. It concentrates its efforts in Butler, Beaver and Lawrence counties.

The addition to the nature preserve, which had been farm fields, belonged for many years to the Taggart family. The conservancy acquired it several years ago with the eventual goal of transferring ownership to the state Department of Conservation and Natural Resources, Mr. Moone said.

"Groups like the conservancy can move a lot faster than the state when land becomes available," Mr. Derr said.

Located south of Slippery Rock Creek and facing West Park Road, the natural area includes a floodplain forest of northern hardwood trees and shrub-scrub wetlands.

"We want people to understand and appreciate nature," Mr. Moone said. "One way to get them to do that is to have places like this, where they can go out and see plants and animals."

The area, which will be kept in as wild a state as possible, is home to many types of birds and animals and to a number of rare plants, Mr. Derr said.

The Wild Waterways Conservancy has been involved with preserving more than 500 acres of green space in the Slippery Rock and Connoquenessing watersheds, Mr. Moone said.

Created in 2002 as The Glades Conservation Alliance, the nonprofit organization adopted its current name in 2005. Conservancy supporters include private foundations and individuals, and its preservation efforts also have qualified for state Growing Greener grants.

The organization is based in Zelienople; former Pittsburgh Mayor Tom Murphy is board president.

"Our goal is to pick up pieces of property that need to be preserved," Mr. Moone said. "Some may have been missed when Moraine and McConnell's Mill [state parks] were created, but they are important to protect."

Moraine State Park covers 16,735 acres -- more than 26 square miles -- and attracts about 1.2 million visitors each year.