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New Off-Road Bird Survey Reveals Importance of Kittatinny Ridge

View from Pulpit Rock along the Kittatinny Ridge; photo by Brian Byrnes.
A survey study conducted in the Kittatinny Ridge Important Bird Area reveals that off-road point counts allow for much higher detection of forest interior songbirds, including many priority birds, in extensive forest systems. Findings demonstrate the efficacy of trail-based point counts in larger scale forests in the AMJV, where many forests are likely under-surveyed and under-appreciated for their importance to high priority species.

The Kittatinny Ridge is a largely forested ridge that extends for 185 miles through southeastern Pennsylvania, extending from the Delaware Gap to the Mason-Dixon Line. It is one of the primary hawk migration routes in eastern North America and designated an Important Bird Area (IBA). The Ridge also constitutes the largest block of contiguous forest in southern Pennsylvania and potentially important for several forest species including high priority species such as Cerulean Warbler. However, since there are few off-road bird population surveys, the size of forest bird populations in this and other large forest blocks are poorly known.  The recently conducted Second Pennsylvania Atlas of Breeding Birds (PBBA), 2004-2009, provided population estimates from point counts. But forest interior habitats were probably under-sampled because the Atlas conducted points only along roads. 

A new study supplements the 2nd PBBA data with off-road point count data. The new data provides advancement in breeding bird population estimations but has biases based on the point locations.  Population estimates produced by this effort will assist in possible Global IBA nomination for the Cerulean Warbler, and will provide a baseline for future comparisons. Researchers referenced each point and collected metrics for land cover type, landform, elevation, and distance to road. They also conducted points on 25 hiking routes, with each route comprising between 12 and 37 points along trails such as the Appalachian Trail and the Tuscarora Trail. 

The results of this study were quite impressive.  A total of 590 points were conducted. There were 88 species detected on point counts with a total of 7,369 individual birds detected in all.  The 20 most frequently detected species accounted for 81% of detections, with Red-eyed Vireo, Ovenbird, and Scarlet Tanager as the most numerous species. Red-eyed Vireos and Ovenbirds were particularly numerous, being detected at 96% and 81% of points respectively.  Among the forest interior songbirds that were of prime interest, Black-and-white Warbler (189) and Hooded Warbler (166) were surprisingly abundant. Other notable totals of forest songbirds include 79 Worm-eating Warblers 57 Yellow-throated Vireos, 54 Cerulean Warblers, 27 Black-throated Green Warblers, and 24 Louisiana Waterthrushes. Estimates were made of Cerulean Warbler densities in the 16 sections designated in the IBA.  These estimates are only possible with large sample sizes (greater than 100 bird detections). 

A comparison of singing males detected per point count in the 2013 study with 2nd PBBA data shows that the forest interior hiking trails allowed for much higher detection of forest interior songbirds, including Cerulean Warbler.  The Cerulean Warblers were detected in distinct clusters with populations estimated to exceed 100 singing males in 5 of the 16 sections with a total estimate of 1,411 singing males, suggesting that this forested area deserves consideration as a Global IBA because of its importance to Cerulean Warbler.  Results from this study are still being analyzed, but they certainly reveal that off-road point counts give much higher population estimates of forest interior songbirds than road-side counts of the same methodology.