Use of Hawkcount.org Data for Wind Energy Siting
Approved by the HMANA Board on 20-April-2010
The Hawkcount database summarizes numbers of raptors counted by experienced observers at HMANA-affiliated count sites. The protocols in use are designed to monitor long term population trends, and are not directly transferable to avian risk assessments for proposed wind energy sites. Count sites are typically located at a vantage point along some particular landscape feature that serves as a pathway for migrating raptors. Landscape features that often concentrate raptors on migration include coastlines and lake shores where water restricts migration (“diversion lines”) or ridges, mountains, and escarpments that provide updrafts conducive to migration (“leading lines”). The count data from a particular site may be representative of raptor migration along a larger migration pathway; however, users are strongly cautioned that the data cannot be extrapolated to other locations without specific knowledge of migration routes used by raptors near and between count sites. Additionally, a lack of count sites in a particular area in no way indicates a lack of migrating raptors, but more likely reflects the unavailability of trained observers and/or suitable vantage points for observation.
In the mid-western, western, and southern portions of the U.S. there are many gaps in the monitoring network. Several western species, such as Swainson's Hawk and Ferruginous Hawk, are not well sampled by the current network of sites, either because of the lack of watch sites or due to the species' dispersed migration patterns. Even in areas where there are many count sites (e.g. Pennsylvania) there are also many locations that based on topography or other landscape features may have concentrations of migrating raptors, but are not regularly monitored or monitored at all. In summary, there are undoubtedly many raptor concentration areas that are currently unknown.
HMANA-affiliated full-time sites typically conduct counts for 7 days per week for approximately 6 to 8 or more hours per day during an entire migration season. Typically counts span March through May in spring and mid-August/September through November/mid-December in fall. Some sites in the Hawkcount database conduct part-time counts or partial season counts, and it is particularly unwise to attempt to extrapolate the magnitude of raptor migration at nearby sites from such data. This is in part because migration counts are often highly variable, from hour to hour, day to day, and year to year, in large part due to variability in weather conditions that provide the lift for raptor migration or concentrates raptors at certain landscape features.
HMANA strongly endorses three-year full-time preconstruction monitoring, utilizing protocols specifically established for avian risk assessment, for proposed wind energy projects located on or near landscape features that may act as leading lines or diversion lines for raptors, as well as in known or suspected migration pathways and wintering or breeding concentration areas. Detailed data on flight patterns and flight altitudes at the proposed wind energy site should be collected for a variety of weather conditions in consultation with state and local experts. Such intensive monitoring will provide the kind of data needed to site turbines in locations where risk to raptors is minimized. We are aware of cases where pre-construction raptor monitoring has consisted of one season (or partial season) of part-time data collection. Such a study design is inadequate for assessing potential risk to migrating raptors, whose movements are likely to be highly episodic (particular weather conditions, times of year, etc).
HMANA recommends that turbines not be sited in areas where raptors concentrate during migration (see policy statement at www.hmana.org). If wind turbines are constructed, continued monitoring during the post-construction period is also needed not only to determine collision mortality, but also to assess how migration patterns are affected by turbines. Currently there is very little published data regarding behavior of migrating raptors near turbines, and it is not clear to what extent turbines may influence or disrupt migration patterns locally or regionally.