Gene Wilhelm walks through his neighborhood in Slippery Rock, listening to sounds that emerge from the woods.

Noting the "creer, creer, creer" overhead, Wilhelm points to a red-shouldered hawk - a male that has just returned to breed.

The birds arrive this time of year from their winter home in the south, he explains: Males first. Females a few weeks later.

Wilhelm said in past years he has observed two breeding pairs of the hawks in Poplar Woods, the housing development where he lives. But smaller lots in the newest phase of the subdivision have meant the loss of trees for nesting.

Although Wilhelm watches birds for pleasure, the retired Slippery Rock University professor is also putting his pastime to use by entering his observations into a statewide database. The entries will be used to produce the 2nd Pennsylvania Breeding Bird Atlas, a five-year project that began in 2003.

The project is being administered by the Pennsylvania Game Commission and the Carnegie Museum of Natural History. Funding came from a U.S. Fish and Wildlife Service grant.

Since the project aims to provide an accurate tally of breeding birds throughout the state, its success depends on volunteers like Wilhelm, said Brian Shema, one of 75 regional coordinators for the atlas.

Shema is director of sanctuaries for Audubon Society of Western Pennsylvania, among other agencies also supporting the project.Since the atlas will account for all corners of the state, residents in all counties are needed to adopt the 10-square-mile "blocks" for observation.The residents spend at least eight hours per year documenting birds during the breeding season, which varies according to species between early spring and late fall, said Shema, who coordinates Region 57."The area measures about 840 square miles," said Shema of his region, which consists of northern Allegheny County and about two-thirds of southern Butler County."I have 42 of 84 blocks adopted - exactly half. A large majority (not yet adopted) are literally centering around the city of Butler."Blocks are available in Clay Township, Concord Township, Oakland Township, Center Township, the City of Butler, Summit Township and Butler Township.

When people volunteer to adopt blocks, they are provided with a list of birds expected to reside in their areas. They also receive detailed maps and information on breeding behaviors, since the presence of a species does not necessarily indicate breeding.On field cards provided by project coordinators, block owners record their observations, later entering the data into a database through the project Web site.People without Internet access can send the field cards through the postal service."I'm really needing block owners as well as just casual participants. I can put (the casual participants) in touch with block owners or I can tell them how to enter their own data. We're using a Cornell database. Anybody can enter data into this data set.""The folks at Cornell basically build the top notch data entry and data analysis Web sites," he added. "Really, the project as a whole is much more advanced than just about any other … I've seen for other states.""The software knows what birds are likely. It also knows what birds could be there. If a bird could be there but is a regional rarity, I get an (automated) e-mail from the database. … In some cases I will go out personally and check and see what bird it is," Shema said.The block owners meet as a group with Shema in the early spring and late fall - before and after their field season - to discuss their successes and failures.The meetings allow new block owners to interact and gain knowledge from veteran birders, or bird-watchers, Shema said. "For the beginning birder, this is a great opportunity to become a full-fledged birder and really enjoy the pastime of birding," he said.Shema said individuals or groups often adopt blocks near areas where they work and live. Avid birders like Wilhelm and those with ample spare time adopt multiple blocks, he added."I would like to see my block owners spend more time than (the minimum eight hours per year)," he said, explaining people with less time are advised to spend their hours "efficiently."Once they have spotted a bird, block owners must decide whether the bird is exhibiting breeding behaviors described in the project literature.

Since the first atlas was produced in the 1980s, the observations will be used to show changes in the state's nearly 200 nesting species, Shema said.Wilhelm, who participated in the first atlas as a regional coordinator, said he has seen the changes firsthand.In addition to fewer red-shouldered hawks in his own neighborhood,Wilhelm is seeing fewer neo-tropical species like scarlet tanagers and rose-breasted grosbeaks. Wilhelm attributes the decline to development, which has taken some of the forested areas necessary for breeding.Shema said one-sixth of all scarlet tanagers in the world breed in Pennsylvania, so the impact of significant habitat loss would be one type of thing the atlas might verify."We'll be able to compare the breeding maps from 20 years ago," Shema said. "We'll be able to do that for every single species.""There is almost a crying need (for documented changes) because we have development everywhere," agreed Wilhelm. "In all these communities we have no model to show what's happening."Dick Nugent of Pittsburgh, another longtime birder, has also seen changes in blocks he has adopted in Butler County. "Canada geese are much more numerous now than they were 20 years ago - as you can ask anyone who plays golf," he explained."Another thing is that, 20 years ago - especially 20 years ago in Butler County - ring-necked pheasants were common breeding birds. Now they are uncommon. … This is the sort of thing the Breeding Bird Atlas is going to uncover."To identify species, Nugent said books and, more importantly, CDs, will aid beginners."A lot of birders now consider it to be birding rather than bird-watching, because in my own mind, we spend a lot of time listening rather than just watching - whereas bird-watching implies you're just using your eyes."Nugent recommends using Peterson's Field Guide To Eastern Birds and a series of three "Birding by Ear" CDs to help with identification. "They cover more than 100 species of birds - just about all the birds you would encounter in Butler County are included in these CDs.""It's a good scientific thing, and it's fun," Nugent said of the project, whose success depends on the volunteers."This project is really suitable for anyone, regardless of their birding identification skills," Shema added. "You don't need this overwhelming skill set when it comes to birds. … Any homeowner can take part in this project.""Its really imperative we get the general public involved, so that even for the most ubiquitous species, we have a list of all the breeding birds within the region or within the state."For more information on the 2nd Pennsylvania Breeding Bird Atlas, log on to www.pabirdatlas.org.