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Fish and Wildlife Research and Management Notes
Authors: John Castrale and Amy Ferchak, Nongame Wildlife Biologists
Date: Feb. 12, 2001 Title:
Midwinter Bald Eagle Survey - 2001
Abstract: The Midwinter Bald Eagle Survey was conducted in Indiana primarily via helicopter from 3-5 and 8 January 2001 and resulted in unprecedented numbers of bald eagles being counted. The 280 bald eagles was way above the previous record of 178 bald eagles tallied in 1996 and the average of 126 for the past 10 years. This large increase is attributed primarily to a continuous period of sub-freezing temperatures that began in mid-December forcing northern eagles and waterfowl to move southward. In spite of these frigid temperatures, rivers in southwestern and south-central Indiana lacked ice cover, providing foraging areas for eagles. Only 11 percent of the eagles were found on frozen lakes and reservoirs, while 89 percent were along rivers. River segments with the greatest concentrations of eagles were the Wabash River in Vermilion (72 eagles), Tippecanoe (31), and Posey (11) counties; Sugar Creek in Parke County (14); the Tippecanoe River in Carroll/Tippecanoe counties (27); and the White River in Lawrence (14), Martin (14), Jackson (8), Morgan (10), Owen (10), and Greene (8) counties. Low numbers (0-3) of eagles were observed at lakes and reservoirs with the exception of Lake Monroe (13). Adults made up 52 percent of the bald eagles observed.
This year’s annual Midwinter Eagle Survey was conducted primarily by helicopter on four days (January 3-5, 8, 2001) and covered over 733 miles of Indiana’s rivers and 313 miles of lake shoreline. The National Biological Service uses data from specific sites to track bald eagle numbers, which have increased dramatically in Indiana and elsewhere. Although the U.S. Fish and Wildlife Service has proposed to remove the bald eagle from the federal list of endangered species, population monitoring for a period of at least five years after delisting is required. Aerial midwinter surveys also provide an efficient way to check on the status of last year’s eagle nests and locate new nests along with great blue heron colonies.
Mid-winter eagle counts have been conducted in Indiana since 1979 and more accurate and complete eagle counts via helicopter have been made since 1990. This year the following reservoirs were surveyed by helicopter: Monroe, Patoka, Lemon, Greenwood, Gallimore, Cataract, Harden, Patton, Bradford Woods, and Gibson. Ground counts on lakes were conducted by DNR and US Fish & Wildlife Service staff at Hovey Lake, J.C. Murphey Lake (Willow Slough FWA), Brookville Reservoir, Eagle Creek Reservoir, and Muscatatuck National Wildlife Refuge. River sections that were surveyed by air include: the Ohio River in Posey County, the Wabash River from the Ohio River to Carroll County (RR bridge), the Tippecanoe River from the Wabash River to the Freeman Lake dam, Sugar Creek from the Wabash River to Deer Mill bridge, the White River from the Wabash River to Interstate 465 in southern Marion County (West Fork) and Seymour (East Fork), and the Patoka River from the White River to Winslow. Although eagles may be found in other sections of the state, the survey sections chosen represent the most consistent wintering sites for bald eagles according to over 20 years of survey data and incidental observations.
Winter weather conditions for this year’s count were more severe than the mostly mild weather normally encountered in December and early January. Beginning in mid-December, subfreezing maximum temperatures set in and continued through the count period. Snow cover was present throughout the state and all lakes were frozen by late December except for some with small holes maintained by waterfowl and those impoundments associated with powerplants (e.g., Gibson Lake). Large southern rivers (Wabash, White, Ohio) were mostly ice free, while smaller rivers and creeks (Patoka River, Sugar Creek) were mostly frozen. The Wabash River was generally ice-covered north of the Cayuga Powerplant in Vermilion/Parke counties, while the Tippecanoe River below Freeman Dam (Carroll Co.) was open almost to where it empties into the Wabash. These weather conditions most likely resulted in more complete southern movements of eagles and waterfowl in areas north of Indiana while unfrozen Hoosier rivers provided abundant foraging opportunities for eagles.
The 2001 midwinter eagle count in Indiana resulted in 280 bald eagles and no golden eagles with an additional 17 bald eagles noted along the Illinois side of the Wabash River and 21 bald eagles in Kentucky around Wabash Island (Fig. 1).These numbers were well above the previous record count of 178 eagles in 1996 and the most recent 10-year average of 126 bald eagles (Fig. 2). Comparisons between years should be made with caution because of differences in areas covered. With few exceptions, river segments had many more bald eagles present than usual, while frozen lakes had fewer than in previous years (Fig. 3). Unprecedented numbers were found along the Wabash River bordering Vermilion/Parke (70 eagles) and Tippecanoe (31) counties, the Tippecanoe River (27), and the White River in Lawrence (14), Greene (8), Daviess/Knox (6), Morgan (10), and Owen (10) counties.
During the survey, 89 percent of the bald eagles were found along rivers, the highest percentage ever recorded and well above the average of 57 percent . Adult eagles made up 52 percent of the total count, well below the average of 63 percent . Only a single bald eagle with orange wing tags, indicating its origin at the Lake Monroe release site was seen (at Patton Lake). Loss of tags and aging of the founding population (all are at least 11-14 years old) result in few tagged eagles being sighted.
Several possible new eagle nests were observed and reports of others indicate that the breeding population could show a substantial increase (as many as seven or more) over the 24 territories known in 2000. Large stick nests that appeared to be eagle nests were observed at Lake Monroe (Monroe Co.) and along the Tippecanoe River (Tippecanoe Co.). Adult eagles were noted standing at nests along Sugar Creek (Parke Co.) and the Wabash River in Gibson County. Other observers reported eagles at nests at Glendale Fish and Wildlife
Area (Daviess Co.), Muscatatuck National Wildlife Refuge (Jackson Co.), and the Patoka River in Gibson County. Monitoring of these nests this spring will be necessary to determine if these areactive bald eagle nests.
Although weather conditions just prior to the survey period have a strong influence on counts in any one year, the value of this nationwide survey is in the analysis of long-term trends on standardized routes summarized by regions. Preliminary analyses for the period 1986-2000 indicate that the number of eagles detected in the Midwest has been increasing 5.6 percent annually, well above the nationwide average of 2.5 percent per year (Karen Steenhof, personal communication). In Indiana, 20 of 22 survey areas analyzed showed increasing trends.
Acknowledgments: Dave Spitznagle, Mark Pochon, Tom Carr, Dawn VanDeman, and Mike Oliver conducted ground surveys for eagles. Ron Whetstone and Dennis Rumley piloted the helicopter and Melody Miller served as an additional observer. This project was funded by donations to the Indiana Nongame and Endangered Wildlife Program from the state income tax check-off.
Locations of bald eagles (dots) during the 2001 Midwinter Bald eagle Survey in Indiana
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Bald eagle numbers on Indiana Midwinter Bald Eagle Surveys, 1979-2001.
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Numbers of Bald Eagles found in selected areas on the Midwinter Bald Eagle Survey.
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