Raptor Population Index

RPI Home

Participating Sites

Analysis

Data Collection

Reports

RPI Contacts, Personnel

hawkcount.org

RPI Analysis

The initial RPI analysis effort examined hourly raptor migration count data from seven hawk watch sites in Canada and the United States. Select a site to view a summary of the initial RPI analysis for that site:

Cape May, New Jersey, USA
Hawk Mountain Sanctuary, Pennsylavania, USA
Hawk Ridge, Duluth, Minnesota, USA
Holiday Beach, Amherstburg, Ontario, Canada
Lighthouse Point, New Haven, Connecticut, USA
Montclair Hawk Lookout, Montclair, New Jersey, USA
Waggoner's Gap, Pennsylvania, USA

Long-term series of data from additional selected sites are currently under analysis. The models to generate annual indices and to calculate long term trends have been described by Farmer et al. (unpublished ms submitted to The Auk in Spring 2006.) In summary, the procedure described by Chris Farmer (North American Monitoring Coordinator, HMSA) standardizes the count day/season at each monitoring site and also allows compensation for missing days and additional covariates (e.g. weather.)

For each species, the model:

(1) Identifies the daily window during which 95% of the migrants are counted;
(2) Selects the seasonal passage window when the middle 95% of the individuals were counted across all years;
(3) Models curvilinear effects of wind speed and direction on number of hawks counted;
(4) Calculates an indices of passage rate [date-adjusted estimated geometric means];
(5) Obtains trends in annual passage rates by fitting a polynomial regression model to the time series of annual indices; and
(6) Re-parameterizes the year terms to determine the significance of these trend estimates (fide Francis and Hussell 1998; Farmer et al. unpublished ms.)

RPI has transferred a series of robust data sets to electronic form for analysis. The analyses underway include the initial seven sites from the Northeast/Great Lakes Region, twelve sites from the Intermountain West Region, and following those there will be a Gulf Region analysis.