Habitat Use by Wintering Bald Eagles in South Dakota

Abstract

Habitat use by wintering bald eagles (Haliaeetus leucocephalus) was surveyed systematically along a section of the Missouri River floodplain in southeastern South Dakota. Main centers of eagle use were associated with a communal roost and a food source. During severe windchill conditions and high wind velocities, eagles moved to protected areas. Eagles preferred tree perches, but also perched on cliffs, ice, partially submerged logs, and on the ground. Eagles perched on stout, horizontal branches that were bordered on at least 1 side by open area. Nearly all perches were within 30 m of the river, and 58% of the perched eagles were within 5 m of the river bank. Eagles preferred mature cottonwoods (Populus deltoides). Distribution of bald eagles at a winter site apparently is influenced most by location of food and areas protected from wind. J. WILDL. MANAGE. 44(4):798-805 Declines in bald eagle numbers (Broley 1958, Sprunt 1969, Braun et al. 1975, Brown 1975) have accentuated the need for intensive habitat management. Habitat requirements for nesting have been identified (Hensel and Troyer 1964, Murphy 1965, Snow 1973, Whitfield et al. 1974, McEwan and Hirth 1979), and areas in some northern forests presently are managed for nesting bald eagles. On the winter range, habitat encroachment by humans is extensive, and eagles now concentrate at scattered locations where habitat and food are readily available. Preservation of winter habitat requires an understanding of the habitat requirements for wintering eagles. Bald eagles are attracted to open water throughout the winter range. General characteristics of bald eagle wintering habitat have been described by Cooksey (1962), Southern (1963, 1964), Swisher (1964), Ingram (1965), Grewe (1966), Edwards (1969), Shea (1973), Lish and Lewis (1975), and Servheen (1975). Stalmaster and Newman (1979) reported perch-preference indices for tree species at a bald eagle wintering area in Washington; however, specific habitat preferences in relation to habitat availability have not been identified in the midwest. The Missouri River below Fort Randall Dam in southeastern South Dakota has been the site of a major winter concentration of bald eagles for several years. Eagles apparently use the area because of the abundant food supply of fish and waterfowl, cottonwood stands bordering the river, and open water throughout the winter. An abundant supply of fish occurs in the 1st kilometer of river immediately I Contribution from the Gaylord Memorial Laboratory (University of Missouri-Columbia and Missouri Department of Conservation cooperating); Missouri Cooperative Wildlife Research Unit (U.S. Fish and Wildlife Service, Wildlife Management Institute, Missouri Department of Conservation, and University of Missouri-Columbia cooperating); Lake Andes National Wildlife Refuge; the National Wildlife Federation; the Office of Biological Services, U.S. Fish and Wildlife Service; the Omaha District, U.S. Army Corps of Engineers; and from the Missouri Agricultural Experiment Station, Project 170, Journal Series 7824. 2 Present address: Snake River Birds of Prey Research Project, Boise District-BLM, 3948 Development St., Boise, ID 83702. 3 Present address: Las Vegas National Wildlife Refuge, Las Vegas, NM 87701. 798 J. Wildl. Manage. 44(4):1980 This content downloaded from 157.55.39.175 on Thu, 11 Aug 2016 06:17:46 UTC All use subject to http://about.jstor.org/terms BALD EAGLES WINTERING IN SOUTH DAKOTA* Steenhof et al. 799 below the dam; fish from the reservoir are pulled through the dam's turbines and fish from the river are attracted to warmer, plankton-rich water in the dam's tailraces (N. Benson, pers. commun.). Our objectives were to identify habitat sites used by bald eagles on the floodplain, structure and species composition of woody habitat, and physical characteristics of trees consistently used by perching eagles. G. F. Krause and S. Ward provided assistance in computer summarization of data and statistical analysis. We acknowledge review of the manuscript by R. D. Drobney, T. E. Martin, M. N. Kochert, and graduate students at Utah State University.