By Kim Van Fleet, Important Bird Area Coordinator and Stacy Small, Director of Bird Conservation
Pennsylvania is unique in that several major migratory bird pathways converge on our state, with its complex topography and geographic position along the Atlantic and Appalachian Flyways. As a result, fall and spring bird migrations are annual phenomena that attract the attention of thousands of birders and wildlife lovers, locally, nationally, and internationally. Audubon Pennsylvania’s Hawk Watch at Waggoner’s Gap, located on the Kittatinny Ridge (Important Bird Area #51), is just one of many locations demonstrating this. Expert volunteer counters at Waggoner’s Gap recorded 21,582 migrating raptors during the 2005 fall migration season, including 14 species of diurnal raptors and two species of vultures. Total species counts are as follows: Black Vulture (95), Turkey Vulture (1814), Bald Eagle (303), Northern Harrier (332), Sharp-shinned Hawk (7020), Cooper’s Hawk (1054), Northern Goshawk (103), Red Shouldered Hawk (267), Broad-winged Hawk (4123), Red-tailed Hawk (4938), Rough-legged Hawk (12), Golden Eagle (242), American Kestrel (397), Merlin (147), Peregrine Falcon (66), and Unidentified Raptors (219).
According to Dave Grove, lead data compiler for the site, “We had an excellent season, finishing with over 21,500 birds, although this year we didn't have any "big days" of Broad-winged Hawk flights,” indicating that the Broad-wings, usually observed at this site, may have utilized an alternate route this year. He further stated that the site set new seasonal records for five species, including Turkey Vulture, Bald Eagle, Cooper’s Hawk, Golden Eagle, and Merlin. Ron Freed, Audubon Pennsylvania’s volunteer site manager and dedicated raptor counter, added “We’re also very pleased with the showing by falcons this year, not only did we set a new high for Merlins, we also saw a rebound in American Kestrel numbers, which had declined in recent years.”
Waggoner’s Gap is one of six ridge-associated Important Bird Areas (IBAs) located within the Valley and Ridge Province of Pennsylvania. All of these IBAs were designated as such due in large part to the high concentrations of raptors and songbirds that utilize them during fall and spring migration. The five other ridge IBAs include IBAs #44 - Second Mountain , #36 Tuscarora Ridge-The Pulpit, #35 - Rothrock State Forest/Stone Mountain, #81 - Greater Tussey Mountain, and #32 Bald Eagle Ridge. Tussey Mountain, Bald Eagle Ridge, and the Allegheny Front are important routes for spring raptor migration, especially Golden Eagles. Additionally, multitudes of birds, including numerous interior forest songbird species, are found nesting on these ridges during spring/summer breeding seasons.
We also know the following about raptor migration in Pennsylvania:
- The ridges of Pennsylvania are oriented in such a way that when prevailing winds strike the slopes of the ridges during fall and spring, updrafts are produced which result in optimal soaring/gliding conditions along the ridges for migratory raptors. Soaring and gliding flight are frequently employed by migratory raptors because both require less energy expenditure than flapping flight. Consequently, tens of thousands of raptors cruise along the ridges and the Allegheny Front in their migratory movements. So, depending on volunteer hawk watch hours, several thousand to 20,000+ raptors may be observed along a single ridge during a single migration season.
- Raptors will often fly directly above the ridges and tend to hug the ridges in flight as wind speed increases. In addition, they are often observed nearer to the ridge during morning and later afternoon hours.
- Raptors hunt for and consume prey throughout migration and frequently stopover during migration to hunt for prey and roost at night.
- A combination of factors most likely influences when and where raptors fly along the ridges, including time of year, time of day, general weather conditions, seasonality of flight, wind direction and wind speed relative to ridge orientation, general ecology of the different taxa, summer and winter ranges of raptors, leading line effect (usually linear landscape features like ridges and rivers), where birds first encounter the ridges, and availability of suitable habitat in route.
Co-author Kim Van Fleet, currently Audubon PA's IBA Coordinator, studied raptor migration across the Valley and Ridge Province over four consecutive fall migration seasons (1991-1994)4. She found that there is annual and species variation in the use of particular ridges for raptor migration. For instance, early season migrants (i.e. Broad-winged Hawk) and more abundant species (American Kestrel) were more commonly observed on the southern ridges. She also found that falcon species more commonly associated with coastal migration, like the Merlin and Peregrine Falcon, were more evenly dispersed across the ridges of the Valley and Ridge Province. Later season migrants like Golden Eagle, Northern Goshawk, and Rough-legged Hawk were more prevalent on the northern ridges.
The mission statement of Audubon PA is to conserve and restore natural ecosystems, focusing on birds and other wildlife, and their habitats, for the benefit of humanity and the earth’s biological diversity. This is foremost in any actions taken by the Pennsylvania state office of the National Audubon Society. Numerous conservation issues have and will continue to arise across the state that directly or indirectly impact forest health on our IBAs, including habitat fragmentation from housing and commercial developments, habitat damage by over-abundant deer, and invasive plant and insect species. Recently, concerns have arisen about wind farm development on numerous ridge-tops in Pennsylvania. Many targeted wind development sites are lands located on ridges along key raptor migration corridors. These ridges also currently comprise large intact forest blocks that support a diversity of breeding interior forest songbirds.
Audubon Pennsylvania supports the development of renewable energy and reduction of fossil fuel dependency. However, Audubon Pennsylvania maintains that wind power development can be accomplished through an ecologically sensitive approach that minimizes wildlife and habitat risks including direct mortality, avoidance of historic migration routes resulting in excessive energy expenditure, and habitat loss and forest fragmentation. Government, non-profit, and industry representatives can achieve this collaboratively by referring to and incorporating current wildlife safety guidelines, including US Fish and Wildlife Service's "Interim Guidelines to Avoid and Minimize Wildlife Impacts from Wind Turbines" 1 and American Bird Conservancy's "American Bird Conservancy Wind Energy Policy," 2 as well as the position statement issued by the Hawk Migration Association of North America.3
In the skies: Pennsylvania is an internationally recognized crossroads of migration for many bird groups, and the ridges of the Valley and Ridge Province and Allegheny Front are utilized heavily by tens of thousands of migrating raptors annually.4 Primary risks for diurnal migrating raptors are direct mortality5 and route avoidance, resulting in disrupted migration patterns and potentially excessive energy expenditure.
On the ground: Many of the areas of proposed ridgetop wind development sites are on Pennsylvania's remaining large unfragmented forests tracts. Pennsylvania has a strong stewardship responsibility for breeding populations of interior forest bird species in the Northeast that depend upon these unfragmented forests.6
Audubon Pennsylvania stands behind the USFWS in calling for three years of pre-construction monitoring, as well as post-construction monitoring and ongoing mortality and risk assessment, conducted by agency biologists and/or those independent of industry. For some ridges, long term data sets are readily available through the Hawk Migration Association of North America www.hmana.org. Other ridgetops will require original data collection. In addition, radar monitoring of nocturnal migrants is currently an available technology to reduce mortality risk for migrating songbirds and other bird groups (D. Mizrahi, pers. comm.). Multi-year pre-construction monitoring is critical because of annual variation in migration routes, due to variation in bird species distribution, weather fronts, and resulting wind conditions.4
Audubon Pennsylvania recommends to avoid siting turbines on ridgetops that concentrate raptors during spring and fall migration, in particular Kittatinny Ridge (Blue Mountain), Tuscarora Mountain, Tussey Mountain, Bald Eagle Ridge, and Allegheny Front. Furthermore, other less well-monitored ridgetops in the Ridge and Valley Province, such as Stone and Jack's Mountain, serve as important migration routes during some periods. 4
In addition, Audubon Pennsylvania advocates the protection of unfragmented forests, Important Bird Areas (IBAs), areas supporting federally and state Threatened and Endangered species, and Landscape Conservation Areas (PA Natural Heritage Program - www.dcnr.state.pa.us/forestry/pndi). More appropriate turbine sites would be post-industrial (brownfield) sites, away from major migratory corridors. We seek to minimize fragmentation of intact forest blocks, as PA currently supports large breeding populations of forest birds. The fragmentation of large forest blocks is listed as a bird population stressor in many of our IBA conservation plans (the plans can be found at http://pa.audubon.org). Siting wind turbines on "brownfields" (post-industrial sites) rather than large, intact forest blocks would minimize such fragmentation and reduce impacts.
Lighting of turbines is to be avoided, as to not attract nocturnal migrating bird flocks. Similarly, adjacent communication and meteorological towers should be lit using rapidly pulsing white strobes, according American Bird Conservancy guidelines, to avoid attracting nocturnal migrants into wind farms. Guy wires at turbines and adjacent towers increase mortality risk, and should be avoided. Similarly, power transmission lines should be run underground.
Audubon Pennsylvania currently is coordinating with Audubon Chapters statewide, as well as meeting regularly in collaborative settings with resource agency and wind industry representatives to advocate for stringent pre- and post-construction monitoring guidelines, ecologically sensitive placement and design of turbines, and an alternative energy policy that minimizes wildlife and habitat impacts.
State office staff recently held a statewide conference call with Chapters to hear from our members on the issues. Participants widely represented regions targeted for wind development, including Presque Isle, Audubon Society of Western PA, Allegheny Plateau, and Juniata Valley in the west, and Lycoming, Seven Mountains, Appalachian and South Mountain chapters in the Ridge and Valley Province. There was general consensus that Audubon supports alternative energy development in the Commonwealth, but that wildlife safety and habitat quality concerns must be on the forefront of all development plans. Audubon Pennsylvania is taking a pro-active approach to the issue by participating in collaborative discussions in Harrisburg and stressing the implementation of nationally developed guidelines for wildlife monitoring, siting, and design criteria for wind turbines, as well as preserving Pennsylvania's highest quality wildlife habitat in the process.
1. Interim Guidelines to Avoid and Minimize Wildlife Impacts from Wind Turbines. 2003. US Fish and Wildlife Service. US Dept. of the Interior. Washington, D.C.
2. American Bird Conservancy Wind Energy Policy. May 2004.
3. Hawk Migration Association of North America. November 2004. Board of Directors Resolution.
4. Van Fleet, P.K . 1997. The Geographic Distributuion of Diurnal Raptors Migrating Through the Valley and Ridge Province of Central Pennsylvania. M.S. Thesis Shippensburg University. Shippensburg PA
5. Hoover, S.L. and M.L. Morrison. 2005. Behavior of Red-tailed Hawks in a wind turbine development. Journal of Wildlife Management 69(1): 151-159.
6. Rosenberg, K. V. and J. V. Wells. 1995. Importance of geographic areas to Neotropical migrant birds in the Northeast. Final report to U. S. Fish and Wildlife Service, Region-5, Hadley, MA.