2nd Pennsylvania Breeding Bird Atlas

Atlas Regions

The "block," the survey unit that is mapped in both Atlasses, is one-sixth of a standard USGS 7.5-minute series topographic maps (also called a quadrangle map , or "topo" or "topo quad" for short). In the 2nd Pennsylvania Breeding Bird Atlas, the Atlas block is the primary survey unit, enabling direct comparisons between the occurrence and distribution of birds between the two Atlas periods. It is this comparison that provides the long-term monitoring component of the atlassing method. Differences in the occurrence and distribution of birds over time may result from many factors, including natural changes in habitat (loss of early successional habitats due to reforestation, perhaps resulting in localized decreases in species like golden-winged warbler and increases in rose-breasted grosbeak), changes in the behavioral ecology of species (e.g., increased tolerance of human activity in common raven and various "urban" raptors), population expansions, and loss of useful habitat for some native nesting birds due to urban sprawl.

One significant organizational change for the 2nd Atlas is doing away with the use of county lines to delineate regional boundaries. Regions for the 1st Atlas largely were based on county boundaries, including one to four counties, and ranging in size from 39 to 306 Atlas blocks. Using counties to define regional boundaries not only resulted in a wide size range for regions, but also a large number of Atlas blocks that fell within two or more regions, requiring decisions over block "ownership" to be made on a case-by-case basis by Regional Coordinators. Rectangular regions defined by the borders of the blocks themselves make for more efficient use of map resources and allow for the establishment of more nearly equal-sized regions and, consequently, more equitable sharing of responsibility among Regional Coordinators.

DeLorme Atlas

For the 2nd Atlas, a significant advancement in map resources, now known to most birders and other outdoor people but not widely known or available during the first Atlas, is the DeLorme Atlas & Gazetteer for Pennsylvania. Although the Atlas block still is the primary sampling unit for the 2nd Atlas, we decided to identify and name coverage regions based on the pages in the DeLorme Atlas.

• Each full map page in DeLorme contains the equivalent of 14 USGS topo quad maps (six Atlas blocks each), for a total of 84 Atlas blocks.
• Along the western border of the state, a small portion of each map page falls outside of Pennsylvania, so those regions (Regions/DeLorme pages 42, 56, and 70) are slightly smaller than 84 Atlas blocks.
• In the case of DeLorme pages that are only half or less within the state, adjacent map pages have been joined together to form one Breeding Bird Atlas region (e.g., 26/28, 27/29, 54/55, 67/68, 82/83, 84/85, 86/87, 88/89, 90/91, 92/93, 94-96).
• The smallest region, Region 40 (and DeLorme page), contains about 55 Atlas blocks, while the largest, Region 67/68, has about 125 blocks.