Volunteers counted 179 bald eagles, 108 golden eagles, and 23 eagles of undetermined species, on new and established survey routes along 1389 miles of public roads. Sightings of several other raptor species were also reported, the most common being rough-legged hawks and red-tailed hawks, and less common being northern harriers and American kestrels. One observer reported a group of Greater Sage-grouse as well.
The Midwinter Bald Eagle survey has been conducted in the Powder River Basin (PRB) since 2006, with 119 eagles counted in that year. The 2007 through 2012 surveys found 300, 162, 269, 288, 290, and 304 eagles, respectively. These survey totals vary due to the number of routes covered in each year, but are also influenced by weather and the availability of food sources including carrion, prairie dogs, and rabbits.
Golden eagle observations retained their high numbers from 2012, which was a 40 percent increase from 2011. Bald eagle numbers were also similar to last year, which remain lower than in previous years. It is unknown why there was a shift in numbers seen in the PRB. The mild weather during these years’ surveys, warm temperatures and clear skies, likely increased eagle activity and visibility. Other explanations could include fluxes in prey populations or severe weather in surrounding regions.
In past years, bald eagle observations were most concentrated in the foothills along Interstate 90 between Sheridan and Buffalo. In these areas, road kill, fish and waterfowl provide valuable winter forage, while trees offer roosting sites where the eagles can keep warm at night. This year, while still mostly concentrated in riparian areas, eagles were more widely distributed.
“Bald eagles were not seen in as large of groups as previous years,” reports Darci Stafford, BLM wildlife biologist. “The mild weather the day of the survey provided ideal foraging conditions for eagles, as exhibited by the number of observations scattered across the resource area away from roosting habitat.”
While hundreds of bald and golden eagles are seen in the Basin during the winter months, only a few stay year-round. Approximately ten to twelve bald eagle pairs nest in the area. A greater number of golden eagles remain in the PRB to breed. The winter populations migrate north in March and April, returning to northern Canada and Alaska.
For the first time in eight years, the survey was postponed in the Buffalo area due to winter weather. Despite the survey being moved to a Friday morning, volunteer turnout remained high, with two new routes surveyed and only one route going uncovered for a total of 59 surveyed routes.
“It’s great to see that the reschedule didn’t bring down volunteer enthusiasm,” said Chicago Botanic Garden and BLM Intern Hillary Duncan. “Volunteer support is really what makes the midwinter survey a success.”
The information gathered from the survey is used by wildlife researchers and managers nationwide, but is also valuable on the local level. The data collected helps the BLM to determine important habitats in the BFO, which consists of Campbell, Johnson, and Sheridan counties. Winter storms led to surveys being rescheduled in the Newcastle and Casper area and in the Bighorn Basin.
The national Midwinter Bald Eagle survey effort began in 1979 as an effort to identify wintering habitat and develop a total population index for the struggling eagle population in the lower 48 states. Collecting eagle data over the long-term has allowed analyses of population trends that help to monitor the health of the species as a whole.
Other regions of the state participated in this yearly survey as well. Wildlife professionals from the BLM, U.S. Department of Agriculture, U.S. Forest Service, National Park Service, and U.S. Fish and Wildlife Service helped coordinate local surveys in the following areas: Casper, Cody, Kemmerer, Lander, Newcastle, Pinedale, Rawlins, Rock Springs, and Worland BLM field offices; Bridger-Teton National Forest; Medicine Bow National Forest; Grand Teton National Park; and Yellowstone National Park. The BLM Cody and Worland field offices have been participating in the survey since the late 1980s, resulting in over 20 years of data that has been used in national population trend analyses.
If you are interested in volunteering next year, or would like additional information, contact Charlotte Darling at 307-684-1045 or Darci Stafford at 307-684-1144. For more information on the national program and its results visit the U.S. Army Corps of Engineers Bird Initiative website at http://corpslakes.usace.army.mil/employees/bird/midwinter.cfm.