Maps/Directions - call HWI at 801-484-6808 to make arrangements for a visit.

Spring 2002 Technical Report
(1.9 Mb PDF Document, requires Adobe Acrobat Reader 5.0 or newer to view)

1999-2002 Count Results

The Rogers Pass spring raptor migration study in west-central Montana is an ongoing effort to monitor long-term trends in populations of raptors, primarily Golden Eagles, using this northern portion of the Rocky Mountain Flyway. Long-time HWI affiliates and veteran raptor observers Fred and Cathy Tilly began studying the eagle migration through Rogers Pass in the late 1980's and conducted the first extended count in the area in 1988. Fred conducted a second extended count in 1990 and in 1992, working under HWI sponsorship and with wife Cathy as the second observer, began conducting annual counts during the month of March. To date, the Tillys have recorded 14 species of migratory raptors at the site, with counts typically ranging between 1,200 and 2,200 migrants per season. Golden and Bald Eagles typically comprise 93-96% of the count, and the month-long effort is designed to sample primarily the adult Golden Eagle migration..

In 2003, HWI conducted or co-sponsored 14 long-term standardized migration counts in 10 states and Vercruz, Mexico. The primary objective of these efforts is to track long-term population trends of diurnal raptors throughout primarily western North America. Raptors feed atop food pyramids, inhabit most ecosystems, occupy large home ranges, and are sensitive to environmental contamination and other human disturbances. Therefore, they serve as important biological indicators of ecosystem health. Moreover, due to the remoteness and widespread distribution of most raptor populations, migration counts likely represent the most cost-effective and efficient method for monitoring the regional status and trends of multiple raptor species

The interface of the Rocky Mountains and Great Plains represents an obvious migratory corridor for raptors, especially Golden Eagles. Prevailing westerly winds along the Rocky Mountain foothills create reliable updrafts for migrating raptors in a nearly continuous line extending from north-central Mexico through New Mexico, Colorado, Wyoming, Montana, and western Canada. The attractiveness of this route for spring, northbound migrants (especially eagles) is enhanced by the abundance of Columbian ground squirrels and black-tailed prairie dogs newly emerged from winter burrows, carrion from spring calving, and migrating waterfowl. All are available on the plains in close proximity to the Rocky Mountain foothills.

Since 1993, the Rogers Pass count has occurred on the private Blacktail Ranch owned by Tag Rittel and Sandra Renner. For this reason, the site is not well-suited to intensive visitation and educational activities; however, prearranged visits by small numbers of people are possible. Those interested in such a visit are encouraged to call the HWI office and make necessary arrangements.

This project will not occur in 2003, primarily because Fred and Cathy Tilly have decided to seek warmth this spring rather than persevere yet again through the bitter wind and cold that often characterizes the weather along the eastern Rockies in March. Because recruiting replacements for the Tilly's on this project is a difficult task, HWI has decided to take this opportunity to evaluate the utility of the data collected thus far and determine whether the project merits continuation in 2004.

Financial support for this project in 2002 was provided Jennifer and Randy Speers, and HWI members.