Introduction

The purpose of this Data Series report is to provide the occasions, locations, and counts when golden eagles were recorded during the annual Midwinter Bald Eagle Surveys. Golden eagles (Aquila chrysaetos) are protected by Federal statutes including the Bald and Golden Eagle Protection Act (BGEPA) (16 USC 668–668c) and the Migratory Bird Treaty Act (MBTA) (16 USC 703–12). The U.S. Fish and Wildlife Service (Service) manages golden eagles with the goal of maintaining stable or increasing breeding populations (U.S. Fish and Wildlife Service, 2009). Development for the generation of electricity from wind turbines is occurring in much of the range of the golden eagle in the western United States. Development could threaten population stability because golden eagles might be disturbed by construction and operation of facilities and they are vulnerable to mortality from collisions with wind turbines (Smallwood and Thelander, 2008). Therefore, the Service has proposed a process by which wind energy developers can collect information that could lead to Eagle Conservation Plans (ECP), mitigation, and permitting that allow for golden eagle management in areas of wind energy development (U.S. Fish and Wildlife Service, 2011).

The Service recommends that ECP be developed in stages, and the first stage is to learn if golden eagles occur at the landscape level where potential wind facilities might be located. Information about where eagles occur can be obtained from technical literature, agency files, and other sources of information including on-line biological databases. The broad North American distribution of golden eagles is known, but there is a paucity of readily available information about intermediate geographic scales and site-specific scales, especially during the winter season (Kochert and others, 2002).

Midwinter Bald Eagle Survey

The Midwinter Bald Eagle Survey (MWBES) is a source of relatively consistent information about the occurrence of golden eagles during January. In 1979, the National Wildlife Federation implemented a collaborative survey to count bald eagles (Haliaeetus leucocephalus) and map their winter-use areas in the contiguous United States (Pramstaller and others, 1979). Initial results were informative (Millsap, 1986) and in 1984, participants were asked to count eagles annually along predetermined, nonoverlapping routes during the first 2 weeks of January, using the same conveyance (for example, aircraft, boat) at approximately the same time of day in well-defined areas. The survey became an annual occurrence, with the stated purpose of monitoring the status of bald eagles wintering in the contiguous United States by estimating national and regional count trends. Currently (2013), this national effort provides useful data for monitoring bald eagles (Steenhof and others, 2002), and it is managed by the U.S. Army Corps of Engineers (USACE). Information about the survey and data about bald eagles can be obtained from U.S. Army Corps of Engineers (2012). Golden eagle data are available because observers are asked to record all golden eagles that they identify during the annual MWBES.

The data presented here are records of golden eagles observed along routes used to count bald eagles. The Midwinter Bald Eagle Survey includes many routes located along river stretches and water bodies where bald eagles were known to occur and that were relatively accessible. We do not know if the routes used for this dataset are representative of the contiguous 48 States because these routes were not randomly selected. The routes are likely biased towards States and portions of States where organizations and individuals were committed to long-term and consistent data collection. Not all routes are surveyed every year. The latitude and longitude information provided is a location somewhere on the route. The extent of survey routes varies from single fixed points to greater than 150 mi, and in some years only portions of routes are surveyed.

Collection and Processing of Records

We extracted the records of golden eagles from the source files of 1980 through 2010, screened the records, filed them in a database, and produced summary statistics and maps. We screened all entries in the MWBES database for those that indicated that a golden eagle was observed and was associated with a registered geographic location and place name or route number. The number of routes surveyed varied among years, and routes were added and removed during the 31 years of effort. We indicated the years in which a route was surveyed relative to the years golden eagles were recorded.

Golden Eagle Records from the Midwinter Bald Eagle Survey

This database (appendix 1) contains 8,511 records of golden eagles from 535 survey routes in 38 States (appendix 2; fig. 1) from 1980 through 2010. The range of years during which annual MWBES surveys were conducted varies among States (table 1) and within that period in some States, some routes were not surveyed every year (appendix 3). Usually only a few golden eagles were recorded most years on most routes, and most routes included records of no golden eagle observations at least once during the survey period (table 1). As many as 97 golden eagles were counted in a year in California on the Lower Klamath Basin route (appendix 3), and among State data, maximum annual records of 10 to 20 birds were recorded regularly on routes (appendix 4).

Among Bird Conservation Regions (BCR), the number of MWBES routes on which golden eagles have been recorded varied considerably (table 2). Three BCRs exhibited comparatively large total counts: 3,818 in the Great Basin, 3,926 in the Northern Rockies, and 1,378 in the Southern Rockies/Colorado Plateau.

Route Locations and Golden Eagle Records

The Midwinter Bald Eagle Survey route locations and annual counts from this Data Series are available in an interactive web mapping application: Golden Eagle Records from the Midwinter Bald Eagle Survey: Map Viewer. The approximate locations of routes can be displayed over Wind Power Classes from a national wind energy assessment of the United States (Elliot and others, 1986) and other relevant data (fig. 2). The route latitude and longitude provided by the volunteer observers can be found in appendix 1 and in table downloads from the interactive web mapping application. We assumed locations were reported based on GSC_North_America_1983. Summary data and annual counts for a single route can be viewed by clicking on a route symbol. Data for multiple routes also can be viewed by State, Bird Conservation Region, or by area specified with a user-drawn polygon. Data for the selected routes are displayed in a table below the map, and selected data can be exported to a comma-delimited text file for use in other applications.

Acknowledgments

The annual MWBES has been completed by thousands of conservation agency personnel and private volunteer “citizen scientists” over the years. Without their cooperation and commitment to bald eagle conservation and long-term data collection, these records would not have been possible. In addition, State coordinators in 42 States participated in the MWBES since 1979 and accomplished most of the “heavy lifting” by organizing the counts each year and providing count data to the national coordinators. The Northwest Alliance for Computational Science and Engineering (NACSE) at Oregon State University, Corvallis, provided database management services and hosts and maintains the public MWBES website and online data entry site used by State coordinators. In particular, Dylan Keon at NACSE provided critical support for our analysis. Prior to the U.S. Army Corps of Engineers assuming management of the MWBES, Karen Steenhof (retired) of the U.S. Geological Survey managed the survey and greatly contributed to the continuity of data gathering over the years.

We thank U.S. Geological Survey employees Linda Schueck for developing the map viewer, Tom Zarriello for assistance, and Ruth Jacobs for help and guidance with aspects of developing this Data Series report. F.B. Isaacs and an anonymous reviewer provided comments about a draft of our manuscript.

References Cited

Dollison, R.M., 2010, The National Map: New viewer, services, and data download: U.S. Geological Survey Fact Sheet 2010–3055, 2 p. (Also available at https://pubs.usgs.gov/fs/2010/3055/.)

Elliot, D.L., Holladay, C.G., Barchet, W.R., Foote, H.P., and Sandusky, W.F., 1986, Wind Energy Resource Atlas of the United States: DOE/CH10093-4, DE86004442, Solar Technical Information Program, Solar Energy Research Institute (now the National Renewable Energy Laboratory), Golden, Colo., accessed February 27, 2012, at http://rredc.nrel.gov/wind/pubs/atlas/.

Kochert, M.N., Steenhof, K., McIntyre, C.L., and Craig, E.H, 2002, Golden Eagle (Aquila chrysaetos), Account 684 in Poole, A., and Gill, F., eds., The birds of North America: The Academy of Natural Sciences, Philadelphia, Pennsylvania, and The American Ornithologists’ Union, Washington, D.C.

Millsap, B.A., 1986, Status of wintering bald eagles in the conterminous 48 states: Bulletin of the Wildlife Society, v. 14, p. 433–440.

Pramstaller, M.E., Clark, W.S., and Logan, D.M., 1979, Preliminary results of the first annual midwinter bald eagle survey: National Wildlife Federation, Washington, D.C., 13 p.

Smallwood, K.S., and Thelander, C.G., 2008, Bird mortality in the Altamont Pass Wind Resource Area, California: Journal of Wildlife Management, v. 72, p. 215–223.

Steenhof, K., Bond, L., Bates, K.K., and Leppert, L.L., 2002, Trends in midwinter counts of bald eagles in the contiguous United States, 1986-2000: Bird Populations, v. 6, p. 21–32.

U.S. Army Corps of Engineers, 2012, National Midwinter Bald Eagle Survey: Website, accessed November 2012, at http://corpslakes.usace.army.mil/employees/bird/midwinter.cfm.

U.S. Fish and Wildlife Service, 2009, Eagle permits; take necessary to protect interests in particular localities: Federal Register, v. 74, no. 175, p. 46836–46879.

U.S. Fish and Wildlife Service, 2011, Draft Eagle Conservation Plan Guidance: 106 p., accessed February 27, 2013, at http://www.fws.gov/windenergy/docs/ECP_draft_guidance_2_10_final_clean_omb.pdf.

First posted March 28, 2013