Sproul State Forest contains about 280,000 acres, mostly in Clinton and Centre counties. The southern half is a state Important Bird Area and this area sustains particularly high breeding densities of about twenty forest scrub and interior breeding birds. Many of these are songbirds whose breeding range extends south through the Appalachians from their core areas further north.
The area’s birds were little studied until Pennsylvania Audubon began to inventory and monitor the IBA’s breeding birds. Around the same time, the author began two Breeding Bird Survey (BBS) routes that traversed the IBA. Each route is run once a year, usually in early June, with 50 stops one-half mile apart. All birds observed within a three-minute period are noted. U.S. Fish and Wildlife Service assesses the status of North American birds from data collected on approximately 2000 routes. This article will primarily summarize the BBS data, with some additional highlights from SAP and Breeding Bird atlas trips.
Sixty-eight species have been observed on the BBS routes, though one may not be a breeder. Another twenty-three species probably breed here in small numbers, for a total of about 90 breeders. Table 1 contains the mean 2002-2004 BBS count for 47 species. If these means rank among the top ten of the 71 Pennsylvania routes run those three years, that ranking is shown. One of the Sproul routes ranks as the top Pennsylvania route for seven species and rank among the top three routes for another seven species. For Chestnut-sided Warbler, and Yellow-rumped Warbler, and Eastern Towhee, these routes rank 1-2. More localized habitats in Sproul are located away from easily-traversed roads, so the birds observed on these routes reflect the more commonly encountered habitats.
The BBS maps show the geographical distribution of birds within the forest. The symbols represent the 2002-2004 mean count for individual stops. Route A starts at the western edge of the state forest, follows little-used state forest roads for 24 stops that include headwater valleys, then along route 144 for 9 stops, including the burn area, then 14 stops along state forest roads that again dip into headwater valleys before ending back on the ridgetop for the last three stops. Route B starts near the West Branch and steeply climbs the plateau with about half the stops along the narrow, northeastern edge of the ridge top before turning south, then east.
Table 1. Mean yearly number of birds for 47 species, 2002-2004. Top-ten ranking among Pennsylvania BBS routes indicated in parentheses.
|Species||A Route||B Route|
|Alder Flycatcher||1.3 (7)||0|
|Least Flycatcher||8.7 (3)||7.7 (4)|
|Great Crested Flycatcher||2.7||2.0|
|Blue-headed Vireo||7.7 (3)||5.0 (9)|
|Common Raven||3.0 (6)||3.7 (3)|
|Veery||7.0 (9)||7.3 (8)|
|Hermit Thrush||9.0 (3)||7.3 (5)|
|Chestnut-sided Warbler||18.3 (2)||20.0 (1)|
|Magnolia Warbler||2.3 (8)||0.7|
|Black-throated Blue Warbler||12.3 (1)||4.3 (5)|
|Yellow-rumped Warbler||6.3 (1)||5.3 (2)|
|Black-throated Green Warbler||24.7 (1)||18.7 (5)|
|Blackburnian Warbler||8.3 (4)||3.0|
|Cerulean Warbler||0||1.7 (4)|
|Black-and-White Warbler||8.0 (3)||7.7 (4)|
|American Redstart||10.7||29.0 (1)|
|Common Yellowthroat||43.7 (1)||31.0|
|Canada Warbler||3.3 (2)||0.7 (9)|
|Eastern Towhee||40.0 (2)||46.0 (1)|
|Rose-breasted Grosbeak||6.3 (2)||4.0|
Red-eyed Vireo was the most common bird found on the Sproul BBS routes, which reflects its numerical dominance in Pennsylvania’s oak forests. Ovenbirds and Scarlet Tanagers are common here, but less so than in the rich oak forest of Rothrock State Forest.
Along the ridge top, where chestnut oak and mountain laurel predominate or in the burn area, a cohort of species reach high densities: Chestnut-sided Warbler, Black-and-white Warbler, Common Yellowthroat, and Eastern Towhee. Where clumps of white pines grow, Yellow-rumped Warbler is often found here. At one mountain-top conifer grove, I observed a Red Crossbill in June, 2004. Alder Flycatcher and Prairie Warblers are regularly found in the burn area.
In headwater valleys or in ridge-top conifer pockets are found a cohort of boreal species: Least Flycatcher, Blue-headed Vireo, Veery, Hermit Thrush, Black-throated Blue Warbler, Magnolia Warbler, Black-throated Green Warbler, Blackburnian Warbler, and Canada Warbler. Black-throated Blue and Black-throated Green Warbler counts averaged higher on the A route than on any other Pennsylvania route during 2002-04.
American Redstart and Rose-breasted Grosbeak can often be found in forest of intermediate succession, on both ridge top and in valleys. American Redstart counts averaged higher on the B route than on any other Pennsylvania route during 2002-04.
Some species common thirty miles to the south in Rothrock’s rich forests are uncommon in Sproul. Wood Thrush and Cerulean Warbler are found on the BBS only along the steep hillside near the West Branch, while Red-bellied and Pileated Woodpeckers, Acadian Flycatcher, Great Crested Flycatcher, Tufted Titmouse, Hooded Warbler, and Worm-eating Warbler are infrequently found.
BBS maps in taxonomic order:
Great Crested Flycatcher
Black-throated Blue Warbler
Black-throated Green Warbler