January 30 , 2006
Contact: Lesley A. Collins
Volunteers Count 123 Eagles During Midwinter Survey:
Three new eagle nests found
Twenty-two volunteers from Campbell, Johnson, and Sheridan counties covered the Powder River Basin on Saturday, January 14, 2006 documenting bald and golden eagle sightings. Volunteers drove 1,000 miles of public roads, counting 80 bald eagles, 36 golden eagles, and seven eagles which they were not able to identify.
Bureau of Land Management (BLM) Buffalo Field Manager Chris Hanson, stated “I am pleased with the public participation in this year’s inaugural survey, and hope to see participation grow in future surveys.”
Brad Rogers, U.S. Fish and Wildlife Service biologist explained why BLM and Fish and Wildlife Service initiated the survey. “We knew the Powder River Basin was important for wintering eagles, but we had no idea of the approximate population, or how the population has changed over time. By repeating the survey annually, wildlife managers will have a better idea of how the local winter eagle population is faring.”
This is not the first effort at understanding the winter ecology of eagles within the Powder River Basin. BLM, Wyoming Game and Fish Department, U.S. Fish and Wildlife Service, and the University of Wyoming cooperated in the mid 1980s to locate eagle winter roost sites.
Bald and golden eagles often roost together at night, particularly if there is a reliable food source nearby. BLM has been repeating the roost searches in recent years, including this winter. However, as Tom Bills, BLM biologist discussed “Roost surveys focus on a limited area each day, so they do not provide much insight into the wintering eagle population. An eagle seen during a roost survey on Monday may be found again in a different area later in the week. Since the midwinter survey covers a large geographic area during a limited period, it should provide us with a more reliable index of population trends.”
During the midwinter survey, most eagles, both bald and golden, were seen in cottonwood riparian areas, along paved highways, within agricultural fields, and near prairie dog towns. These results support the roost survey effort in that eagles are found near food resources. Riparian areas provide fish and waterfowl, highways provide road kill, agricultural fields supply mice and other small mammals, and prairie dogs are an eagle delicacy. Very few eagles were seen in rural upland rangelands. “Particularly the lack of golden eagles in these rural rangeland areas was a little surprising,” said Tom Bills, “I expected to see more golden eagles in the rangeland communities hunting for rabbits and other small mammals.”
The current winter roost surveys have also found most eagles to be roosting within riparian cottonwood groves. An interesting change in eagle ecology from the roost surveys in the mid 1980s is that historically eagles were found roosting in upland ponderosa pine forests as well as along the drainages. Again, available food is the key. During the 1980s, there were many large domestic sheep ranches within the Powder River Basin and eagles fed on winter killed sheep. With the decline of the domestic sheep industry, eagles have adapted to other food sources.
In contrast to the 80 bald eagles seen during the midwinter survey, there are only 10 to 12 bald eagle pairs annually nesting within the Powder River Basin, primarily along fish-bearing streams and rivers in Sheridan County. The true nesting population of golden eagles within the basin is not known. BLM, Wyoming Game and Fish Department, and coalbed natural gas companies have been surveying throughout the Basin for several years to identify golden eagle nests and nests of all raptor (birds of prey) species. To date, 105 nests have been identified as golden eagle nests, with nesting activity confirmed at 25 of these nests in 2005.
The midwinter survey is part of a national effort which began in 1979 to establish an index of the total winter bald eagle population in the lower 48 states. Participants are asked to count eagles along standard routes to identify population trends.
If you are interested in volunteering next year, or for additional information, contact Tom Bills at 307/684-1133 or Brad Rogers at 307/684-1046. For more information on the national program visit the U.S. Geological Survey Snake River Field Station web site at http://srfs.wr.usgs.gov/research/indivproj.asp?SRFSProj_ID=2.