Our Liviiis; Ri'stiiiives — Glohcil Climate Change 



389 



and numerous hydroelectric plants built with 

 cooling ponds provide open water in winter, 

 which this eagle needs for hunting (Southern 

 1963). 



The winter abundance of the bald eagle 

 throughout most of the contiguous United 

 States dropped by about a third from 1957 to 

 1970 because of the use of persistent insecti- 

 cides (e.g.. DDT) and habitat destruction 

 (Brown 1975). Since World War II. population 

 declines in the East have been blamed on habi- 

 tat destruction due to human disturbances 

 (waterfront housing and outdoor recreation; 

 Sprunt 1969). Shooting by ranchers from small 

 planes from the late 1930's to the early 1960"s 

 could have depressed their abundance during 

 this period and later (USFWS 1992). 



Range Contractions 



Of the 58 species examined, only 4 showed 

 range contractions. This result could have been 

 partly an artifact of our sample: we did not 

 examine species that have very restricted 

 ranges. It may also be due to our methods of 

 examination because species had to abandon 

 entire states, not just part of them, before we 

 recorded a contraction. Of the four species 

 showing range contractions, one is the brown- 

 headed cowbird (Molotbrus ater) and the other 

 three depend on open water: pied-billed grebe 

 (Podilymbus podiceps), northern pintail {Anas 

 acuta), and common merganser (Mergus mer- 

 ganser). 



The contraction of the northern pintail is of 

 particular concern (Fig. 6). This game species 

 has been extensively managed, yet estimates of 

 its breeding population have shown a fivefold 

 decrease since the mid-1900"s (USFWS 1992). 

 The reasons for this large decline are not yet 

 understood. 



Conclusion 



The data collected by volunteers for the 

 National Audubon Society's Christmas Bird 

 Counts provide excellent information to exam- 

 ine the ranges and abundance patterns of win- 

 tering North American birds over both a very 

 broad spatial scale and a long temporal scale. 

 The changes that we found were primarily due 

 to human activity, both purposeful (e.g., man- 

 agement of game species) and accidental. Some 

 of these changes could be viewed as being ben- 

 eficial (e.g., water management programs 

 increasing bald eagle numbers), while others 

 could be viewed as negative (e.g., logging 

 allowed barred owls to invade spotted owl terri- 

 tories). 



Bald eagle 



Northern pintail 



■ 0.71-1.00 



■ 0.46-0.70 

 m 0.26-0,45 



□ 0-11—0,25 



□ C.01-0,10 



□ 



□ No data 



Fig, 5, Range and abundance patterns of the bald eagle, (a) Data from 1901 to 1940. (bl Data 

 from 1960 to 1989 (except 1969). 



References 



Bent. A,C, 1949, Life histories of Nonh American thrushes, 

 kinglets, and their allies. United States National Museum 

 Bull 196. 4S4pp. 



Bock. C.E.. and L.W. Lepthien. 1976. Population growth in 

 the cattle egret. Auk 93:164-166. 



Brown. W.H. 1975. Winter population trends in the bald 

 eagle. American Birds 29:12-14. 



Ehrlich. P.R.. D.S. Dobkin, and D. Wheye. 1988. The bird- 

 er's handbook. Simon and Schuster, New York. 785 pp. 



Hewitt. O.H. 1967, The wild turkey and its management. 

 Wildlife Society. Washington. DC. 589 pp, 



Lewis. J.C. 1973. The world of the wild turkey. J.B, 

 Lippincott Co., Philadelphia. PA. 158 pp. 



Root. T.L. 1988a. Atlas of wintering North American birds. 

 University of Chicago Press. IL. 312 pp. 



Root. T.L. 1988b. Environmental factors associated with 

 avian distributional boundaries. Journal of Biogeography 

 15:489-505. 



Root, T.L. 1991. Positive correlation between range sizes 

 and body size: a possible mechanism. Proceedings of the 

 Twentieth International Ornithological Consress 2:817- 

 825. 



Root. T.L.. and J.D. Weckstein. 1994. Changes in distribu- 

 tion patterns of select wintering North American birds 

 from 1901 to 1989. Pages 191-201 m J,R, Jehl. Jr and 

 N.K. Johnson, eds. A century of avifaunal change in 

 western North America. Studies in Avian Biology 15. 



Schorger, A.W. 1966. The wild turkey: its history and 

 domestication. University of Oklahoma Press, Norman. 

 625 pp. 



Sharp. D.V. 1989. Range extension of the barred owl in 

 western Washington and first breeding record on the 

 Olympic Peninsula. Journal of Raptor Research 23:179- 

 180. 



Southern, W.E. 1963. Winter populations, behavior and 

 seasonal dispersal of bald eagles in northwestern Illinois. 

 Wilson Bull. 75:42-55. 



Sprunt, A., IV. 1969. Population ttends of the bald eagle in 

 North America. Pages 347-351 in J. Hickey, ed. 

 Peregrine falcon populations: their biology and decline. 

 University of Wisconsin Press, Madison. 



Taylor A.L.. and E.D. Forsman. 1976. Recent range exten- 

 sions of the barred owl in Western North America, 

 including the first records for Oregon. Condor 78:560- 

 561, 



USFWS. 1992. Status of waterfowl and fall flight forecast. 

 U.S. Fish and Wildlife Service. Office of Migratory Bird 

 Management. 30 pp. 



Wing, L. 1947. Christmas census summary 1900-1939. 

 State College of Washington. Pullman. Mimeograph. 



Fig, 6, Maps showing range and 

 abundance patterns of the northern 

 pintail, (al Data from 1901 to 

 1940, (b) Data from 1960 to 1989 

 (except 1969). 



For further information: 



Terry L. Root 



University of Michigan 



School of Namral Resources and 



Environment 



430 E. University 



Ann Arbor, MI 48109 



