Comprehensive Coverage

During field years 2004 through 2009, Second Pennsylvania Breeding Bird Atlas volunteers completed surveys in all of the 4,937 atlas blocks. In achieving this feat, 854,773 bird records were submitted. This massive undertaking documented 218 species (plus two hybrids), of which 190 were considered breeding during this period. Compiled at the block level, the result is an average of 69.5 species per block, or about 74 percent of targeted species lists. About 1,900 atlas volunteers contributed data to the project, tallying 106,952 volunteer field hours and another 34,192 administrative hours, and reported 890,000 miles completing fieldwork.  Comparisons with Pennsylvania’s first Atlas (1983-1989) should keep in mind that about 30 percent more effort was invested in the second Atlas than the first, resulting in generally greater coverage. As a result, species were likely to show fuller block coverage in the second Atlas, and declines should generally be treated as more significant than expansions of range.  

Major Discoveries

One hundred and eigthy-seven species were confirmed to have bred during Pennsylvania’s second Atlas. Included among these confirmed breeders are four which had never been documented to nest in Pennsylvania prior to the second Atlas: Trumpeter Swan, Merlin, Great Black-backed Gull, and Eurasian Collared-Dove. Additionally, the Double-crested Cormorant, Sandhill Crane, and Blackpoll Warbler had not nested in Pennsylvania at the time of the first Atlas, and they represent new species for atlas projects in Pennsylvania. Other historic nesters, confirmed breeding in the second Atlas but not during the first, were Ring-billed Gull, Herring Gull, and Red Crossbill.

The second Atlas documented major range expansions in a number of species. Notable among these is the Clay-colored Sparrow, not confirmed breeding in the first Atlas, and increasing over ninefold, from three block records in the first Atlas to 29 in the second. The Bald Eagle expansion, by over tenfold, and the fivefold increase in Peregrine Falcons, have been documented by ongoing monitoring by the Pennsylvania Game Commission. Impressive, by sheer numbers, is the doubling of blocks documenting Canada Goose, the largest increase in number of block records (1,816) of any breeding bird.

Twice as many bird species associated with forests experienced range expansions overall (19 contracting species, 40 expanding species).  Of particular interest are the 14 strong expansions (>50%) among birds associated with the Northern Hardwood guild. Generalist and Urban specialists have fared even better overall, with 15 expansions and only four contractions, of which three are aerial insectivores (Common Nighthawk, Purple Martin, Cliff Swallow). In contrast, species in the Farmland/Grassland Grassland guild were much more likely to have shown range contractions than expansions. Similarly, results for wetland species (many of which are scarce and localized in Pennsylvania) also skew strongly negative, with 16 of the 26 species showing modest or strong range contractions or extirpation.

The innovative population estimate effort provided sufficient data from point count surveys to derive population estimates for 115 species, including the majority of common songbirds. No less than 23 species achieve total population sizes of more than one 1 million adult birds; the three most abundant species, Red-eyed Vireo, Chipping Sparrow, and Song Sparrow.  Combining all species, approximately 100 million individual birds attempt to nest in Pennsylvania each year.