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SALT LAKE CITY, UT -- HawkWatch International (HWI), based in Salt Lake City, Utah, is working to learn more about raptor populations and their migrations.
In September and October 2002, researchers put 36 satellite transmitters on migrant Red-tailed Hawks, Northern Goshawks, and Golden Eagles in three distinct western flyways at migration study sites in New Mexico, Nevada, Oregon, and Washington. This effort more than doubled the number of transmitters deployed by HWI since initiating satellite telemetry studies in September 1999, bringing the total to 68. The addition of satellite telemetry to HWI migration studies allows more detailed delineation of migratory routes and stop-over points, helps to determine fidelity to migration flyways between seasons and years, and aids in more accurate matching of migration monitoring sites with specific nesting populations. The latter is crucial information for interpreting population trends and identifying possible habitat conservation needs for these powerful, majestic birds.
Target species were selected for a number of reasons, including: abundance (Red-tailed Hawks), recent concerns about negative population impacts related to widespread habitat alterations (Golden Eagles and Northern Goshawks), complicated movement patterns (all species), and the difficulty of adequately monitoring populations through conventional migration studies (all three species have a significant proportion of their population that is non-migratory). A final consideration was the size of the birds; the weight of the transmitter is a limiting factor and cannot be more than 3% of the bird's weight, so only a few raptor species are large enough to carry the small units.
Tracking summaries and maps from all 68 birds fitted with transmitters in 1999, 2000, 2001, and 2002 are now available on-line at http://www.hawkwatch.org Visitors to the website can trace the movements of tagged birds from their banding sites to their wintering grounds, through spring migration, and back to their breeding grounds in summer.
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